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Improvements to the design of the Jet engines
experiment
A dissertation submitted to the University of Manchester for the
degree of Master of Science in Thermal Power & Fluids
Engineering in the Faculty of Engineering and Physical Sciences
2013
Gaurav Gururaj Shenoy
School of Mechanical, Aerospace and Civil Engineering
2
Table of Contents
List of Figures ...................................................................................................................5
List of Tables.....................................................................................................................7
Nomenclature....................................................................................................................8
List of Abbreviations.........................................................................................................8
Abstract .............................................................................................................................9
Declaration......................................................................................................................10
Copyright ........................................................................................................................11
Acknowledgement...........................................................................................................12
Chapter 1 INTRODUCTION..........................................................................................13
1.1. Background........................................................................................................13
1.2. Role of Micro-Jet engines in Education ............................................................13
1.3. Objectives ..........................................................................................................15
Chapter 2 LITERATURE SURVEY .............................................................................17
2.1. Background........................................................................................................17
2.2. Findings .............................................................................................................17
2.2.1. Design of a Turbojet Engine Lab for Propulsion Education (Leong et al,
2004) ....................................................................................................................17
2.2.2. Ten years of experience with a small jet engine as a support for education
(Léonard et al, 2009)...............................................................................................19
2.2.3. Developing a jet engines experiment for the energy systems laboratory
(Pourmovahed et al, 2003)......................................................................................22
3
2.2.4. Micro-Jet test facility for Aerospace Propulsion Engineering Education
(Juste et al, n.d.) ......................................................................................................24
2.2.5. Development of test stand for experimental investigation of chemical and
physical phenomena in Liquid Rocket Engine (Santos et al, 2011) .......................26
2.2.6. Data Analysis and Performance Calibration of a small turbojet engine
(Bakalis and Stamatis, 2011)...................................................................................28
2.2.7. Design of a small jet engine test system for university education (Tanabe et
al, 2003)...................................................................................................................31
2.2.8. Operating experience with the Turbine Technologies SR-30 turbojet engine
test system (Callinan and Hikiss, 2002)..................................................................32
2.2.9. Characterising the performance of an SR-30 turbojet engine (Witkowski et
al, 2003)...................................................................................................................35
2.3. Summary............................................................................................................37
2.4. Conclusion.........................................................................................................39
Chapter 3 DESIGN METHODOLOGY & MODELING...............................................40
3.1. Background........................................................................................................40
3.1.1. Finite Element Analysis..............................................................................40
3.1.2. Design Criterion – Distortion Energy Density Criterion ............................41
3.1.3. About the software......................................................................................41
3.2. Selection of Material for the structure...............................................................42
3.3. Modeling............................................................................................................43
3.3.1. Design 1 ......................................................................................................45
3.3.2. Design 2 ......................................................................................................46
3.3.3. Design 3 ......................................................................................................47
3.3.4. Design 4 ......................................................................................................48
4
3.4. Input parameters for Simulation........................................................................48
3.4.1. Definition of Material .................................................................................48
3.4.2. Fixture & Loading details...........................................................................49
3.5. Summary............................................................................................................50
Chapter 4 RESULTS AND DISCUSSION.....................................................................51
4.1. Thrust Measurement..........................................................................................51
4.2. Simulation results ..............................................................................................52
4.3. Other Parameters ...............................................................................................56
Chapter 5 INSTRUMENTATION IMPROVEMENTS .................................................58
Chapter 6 CONCLUSION AND SCOPE FOR FUTURE WORK.................................62
6.1. Conclusion.........................................................................................................62
6.2. Scope for future work........................................................................................63
References:......................................................................................................................64
5
List of Figures
Figure 2-1 Arrangement of the MW-54 showing instrumentation (Source: Leong et al,
2004) .......................................................................................................................18
Figure 2-2 Aluminum plate suspended using steel wires (Source: Léonard et al, 2009)20
Figure 2-3 (a) Load cell mounted to the test floor (b) Completed arrangement of the SR-
30 (Source: Léonard et al, 2009).............................................................................21
Figure 2-4 Arrangement of calibrated nozzle as an air flow meter measurement device
(Source: Léonard et al, 2009)..................................................................................21
Figure 2-5 Mounting arrangement of the SR-30 at Kettering University (Source:
Pourmovahed et al, 2003) .......................................................................................24
Figure 2-6 (a) Mounting arrangement of the Olympus HP (b) Schematic representation
of pressure and temperature probes at various stations (Source: Juste et al, n.d.)..26
Figure 2-7 (a) Schematic arrangement of the L5 (b) AutoCAD drawing of the
arrangement (Source: Santos et al, 2011) ...............................................................27
Figure 2-8 Schematic arrangement of sensors around the Olympus HP (Source: Bakalis
& Stamatis, 2011) ...................................................................................................29
Figure 2-9 (a) Pressure and temperature v/s engine speed at compressor exit (b) pressure
and temperature v/s engine speed at turbine exit (c) TIT and thrust v/s engine speed
(Source: Bakalis & Stamatis, 2011)........................................................................30
Figure 2-10 Mounting arrangement of the custom small-scale jet engine at Nihon
University, Japan (Source: Tanabe et al, 2003) ......................................................31
Figure 2-11 Standard mounting arrangement of the SR-30 at Loyola Marymount
University (Source: Callinan & Hikiss, 2002) ........................................................34
Figure 2-12 Thrust v/s engine speed obtained during experiments (Source: Callinan &
Hikiss, 2002) ...........................................................................................................34
6
Figure 3-1 (a) Exploded view of design 1 (b) Schematic arrangement of design 1........45
Figure 3-2 (a) Exploded view of design 2 (b) Schematic arrangement of design 2........46
Figure 3-3 (a) Exploded view of design 3 (b) Schematic arrangement of design 3........47
Figure 3-4 (a) Exploded view of design 4 (b) Schematic arrangement of design 4........48
Figure 3-5 Fixture and loading details on (a) Design 1 (b) Design 2 (c) Design 3 (d)
Design 4 ..................................................................................................................49
Figure 4-1 Von-Mises stresses in (a) Design 1 (b) Design 2 (c) Design 3 (d) Design 4 –
AISI 1020 Steel material.........................................................................................52
Figure 4-2 Displacements in (a) Design 1 (b) Design 2 (c) Design 3 (d) Design 4 – AISI
1020 Steel Material .................................................................................................53
Figure 4-3 Strains in (a) Design 1 (b) Design 2 (c) Design 3 (d) Design 4 – AISI 1020
Steel material...........................................................................................................53
Figure 4-4 Von-Mises stress in (a) Design 1 (b) Design 2 (c) Design 3 (d) Design 4 –
Aluminum 1060 Alloy ............................................................................................54
Figure 4-5 Displacements in (a) Design 1 (b) Design 2 (c) Design 3 (d) Design 4 –
Aluminum 1060 Alloy ............................................................................................55
Figure 4-6 Strains in (a) Design 1 (b) Design 2 (c) Design 3 (d) Design 4 – Aluminum
1060 Alloy...............................................................................................................55
7
List of Tables
Table 1 - Details on different sensors at stations (Source: Bakalis & Stamatis, 2011)...29
Table 2 - Results obtained for the SR-30 at LMU (Source: Callinan & Hikiss, 2002) ..35
Table 3 - Temperature at the compressor exit calculated using three different methods
(Source: Witkowski et al, 2003)..............................................................................36
Table 4 - Results obtained on the SR-30 at the University of Minnesota (Source:
Witkowski et al, 2003)............................................................................................37
Table 5 - Summary of literature review..........................................................................38
Table 6 - Material properties (Source: SolidWorks 2012 material library)....................42
Table 7 Summary of results ............................................................................................56
Final Word Count – 11,912
8
Nomenclature
Uo – Total strain energy
Uv – Strain energy causing volumetric change
UD – Strain energy causing distortion
σ1, σ2, σ3 - Principle stresses
K – Bulk modulus
G - Rigidity modulus
List of Abbreviations
ABET – Accreditation Board of Engineering and Technology
CAD – Computer Aided Design
ECU – Engine Control Unit
EGT – Exhaust Gas Temperature
IAE – Institute of Aeronautics and Space
LOX – Liquid Oxygen
LPL – Liquid Propulsion Laboratory
MGT – Micro Gas Turbine
NPSA – National Plan of Space Activities
RPM – Revolutions Per Minute
TIT – Turbine Inlet Temperature
UAV – Unmanned Aerial Vehicle
9
Abstract
Education about propulsion systems has been an important area of study over a number
of years. In order to provide a practical approach for students, many Universities have
adopted the technique of using small-scale jet engines to demonstrate the
thermodynamics propulsion systems. This has become easier with the recent
development of such jet engines for radio controlled aircraft. Small-scale jet engines are
essentially the same jet engines that we see in an aircraft, but smaller in capacity, size,
power and some other operating parameters. Factors like temperature, pressure etc. can
be similar to those on full size jets. In order to study the performance of a jet engine, the
parameters have to be monitored continuously and the performance analysis can be
carried out in different ways (analytical, theoretical or computational). The first part of
the study aims at looking at the literature for the methods adopted in mounting such
small-scale engines and instrumentation implemented. The second part looks at
different designs developed to mount the small-scale engine, a finite-element study in
these designs and studying the maintenance, safety factors involved in these designs.
Choosing the optimum design and any suggestions to the improvements in
instrumentation follows an overall study of the design. A modified version of the
mounting structure adopted by Léonard et al (2009) was chosen to be the optimum
design.
10
Declaration
No portion of the work referred to in the dissertation has been submitted in support of
an application for another degree or qualification of this or any other university or other
institute of learning.
11
Copyright
i. The author of this dissertation (including any appendices and/or schedules to
this dissertation) owns certain copyright or related rights in it (the “Copyright”)
and s/he has given The University of Manchester certain rights to use such
Copyright, including for administrative purposes.
ii. Copies of this dissertation, either in full or in extracts and whether in hard or
electronic copy, may be made only in accordance with the Copyright, Designs
and Patents Act 1988 (as amended) and regulations issued under it or, where
appropriate, in accordance with licensing agreements which the University has
entered into. This page must form part of any such copies made.
iii. The ownership of certain copyright, patents, designs, trade marks and other
intellectual property (the “Intellectual Property”) and any reproductions of
copyright works in the dissertation, for example graphs may not be owned by
the author and may be owned by third parties. Such Intellectual Property and
Reproductions cannot and must not be made available for use without the prior
written permission of the owner(s) of the relevant Intellectual Property and/or
Reproductions.
iv. Further information on the conditions under which disclosure, publication and
commercialization of this dissertation, the Copyright and any Intellectual
Property and/or Reproductions described in it may take place is available in the
University IP Policy (see
http://documents.manchester.ac.uk/display.aspx?DocID=487), in any relevant
Dissertation restriction declarations deposited in the University Library, The
University Library’s regulations and in The University’s Guidance for the
Presentation of Dissertations. (See
http://www.manchester.ac.uk/library/aboutus/regulations)
12
Acknowledgement
I would like to express my sincerest gratitude to my dissertation guide Dr. Andrew
Kennaugh for presenting me with this exciting topic for my dissertation, guiding me
throughout the process of research undertaken. His valuable advises have been helpful
in successful completion of this dissertation.
I would like to take this opportunity to thank my father for giving me all the support and
my mother for her unconditional love and confidence in me, which has helped me in
pursuing my education so far.
I would like to thank Late Prof. K Sridharan, Retired Professor in Civil Engineering,
Indian Institute of Science, Bangalore, who was my inspiration to pursue this field of
engineering and motivated me to continue further.
Finally, I would like to thank all my friends and family for supporting me throughout
my career and helping me go through ups and downs of life.
13
Chapter 1
INTRODUCTION
1.1. Background
Aerospace engineering has seen major improvements in many areas with the
advancements in technology. These improvements are also seen amongst the number of
students opting to pursue education in this field of engineering. Under the Bologna
Initiative in Europe, steps are being taken to produce well-trained professionals and
recruit them into leading companies that compete on a global scale (Juste et al. n.d.).
Juste et al. (n.d.) suggested many different ways to improve the quality of Aerospace
education. A more concurrent engineering approach was suggested during the course.
Jet propulsion is one of the very important topics in the field of Aerospace engineering,
which originated in the beginning of the 20th
century (Juste et al., n.d.; Mattingly, 2006).
However, there has been a rapid development in gas turbine engine technology since the
1950s (Royce Plc, 1986). In 1930, Frank Whittle developed the first gas turbine engine,
which produced a propulsive jet and further went on to form a basis to the modern jet
engines (Royce Plc, 1986).
1.2. Role of Micro-Jet engines in Education
Higher education in this aspect of engineering often requires the understanding of jet
propulsion by experimental or practical means (Perez-Blanco, 2003). In the course of
understanding the science and technology, the process of experimentation and
implementation is crucial (Perez-Blanco, 2003). The study of jet propulsion involves the
design and implementation of prime movers for a large number of different
applications. However, studying jet propulsion or jet engines involves an all-inclusive
understanding of their working in the theoretical, computational and design aspects
14
(Juste et al, n.d.). Often, students find it difficult to understand the theory behind jet
propulsion, as the jet engine is not something they come across in their day-to-day
activities (Tanabe et al, 2003). In order to study the principle of jet propulsion in a
practical sense, a small-scale jet engine or a Micro Gas Turbine (MGT) would be a
good tool, bearing in mind the cost. Micro Gas Turbines are gas turbines, which are
smaller in size and develop a power of up to 200kW. The pressure conditions in such
engines are much smaller than those in bigger jet engines. However, the temperature
conditions in small jet engines are similar to their bigger counterparts. The pressure
ratio in these engines is low (Lee et al, 2007), typically around 4 compared to 15 in
larger engines. This is because of the fact that small-scale engines are mostly single
spool engines. These kinds of engines are used in universities for
demonstration/experimental purposes and also to power unmanned aerial vehicles
(UAV), remote-controlled aircrafts etc. (Benini & Giacometti, 2007).
The use of a laboratory turbojet engine is desirable because of its ease to enable
understanding the thermodynamic principles involved. Apart from this major advantage,
the small turbojet engine is present-day device, which has great potential for
improvement (Callinan & Hikiss, 2002). The ABET syllabus encouraged the use of
laboratory turbojet engines with the aim of imparting knowledge on the working of the
engine components and the whole system itself (Callinan & Hikiss, 2002; Leong et al,
2004). Bearing in mind the theoretical knowledge gained in classroom teaching, the
laboratory turbojet engine is a useful tool to gain hands-on experience while working on
it (Leong et al, 2004). Comparative studies also helps in understanding the behavior of
different types of jet propulsion systems (turbojets, turbofans, turboprops) of different
scales, as carried out by students at the West Michigan University (Leong et al, 2004).
15
One such jet engine in the engine-testing laboratory of the School of Mechanical,
Aerospace and Civil Engineering (MACE) at the University of Manchester suffered a
structural failure causing the exhaust duct to deform and jam against the turbine. This
meant that a new engine was required with the choice being a direct replacement or the
purchase of a different jet. It was decided to obtain a new type of jet engine and this
meant the test stand required a new design for the engine to be mounted upon and also
facilitating the instrumentation to record some additional pressures and temperatures
etc. The objectives of the experiment include understanding the basic working principle
of a jet engine; relating them to the various thermodynamic equations that are
encountered in the theory, gain a brief insight on the use of instrumentation in the
apparatus.
1.3. Objectives
The School of MACE at the University of Manchester recently procured an Olympus
HP electric-start jet engine manufactured and sold by AMT, Netherlands. This jet
engine is capable of producing a maximum thrust of 230N at a maximum engine speed
of 108,500 revolutions per minute (rpm) (AMT Netherlands, 2009). The engine is
specifically modified by the manufacturer for University use and has additional
connections for pressure and temperature measurements beyond those used for routine
radio controlled operation. The objectives of the study cover the various designs of test
stands that have been adapted in mounting such small size jet engines, looking up to the
design factors like maintenance, reliability, safety and convenience of such designs and
also the instrumentation involved in recording different parameters during the working
of the engine. Furthermore, new designs will be developed and studied in the later part
of the thesis.
16
As the test stand is a very important piece of equipment in the process of studying the
engine, more importance was given in the design of the same. The primary requirement
of the design was to make sure the test stand could take the maximum thrust produced
by the engine with minimal distortion or deflection. Adding to this, it was kept in mind
that the test stand required minimum maintenance and ensured safety of the personnel
and surrounding in the unlikely event of any mechanical failure.
This report consists of a literature survey that gives an insight of the different methods
adopted to mount a small scale jet engine, different instrumentation adopted in the
experimental setup and a brief outline of the results obtained. The literature review is
followed by a methodology and modeling chapter, which lays out a briefing on the
methods adopted in working towards the objective, and also the different arrangements
modeled using a CAD package. Results are presented and discussed in the following
chapter followed by the conclusion and recommendations for future work, if any.
17
Chapter 2
LITERATURE SURVEY
2.1. Background
The aim of this literature survey is to understand the different types of test stands that
have been incorporated in mounting small sized jet engines, various measuring
techniques adapted in recording the different operating parameters during the working
of the engine. Adding to this, the literature briefly covers the results that have been
obtained while testing different small size engines. A detailed contribution of different
authors has been presented in the succeeding section.
2.2. Findings
2.2.1. Design of a Turbojet Engine Lab for Propulsion Education (Leong et al,
2004)
As a supplement to the theoretical knowledge gained in the classroom, two graduate
students and a professor from the School of Mechanical and Aeronautical Engineering,
West Michigan University, USA, developed a jet engine test cell facility. The engine
used was a simplified, scaled down version of a turbojet engine - MW-54, developed by
Wren Turbines Ltd. This jet engine works on the Brayton cycle and comprises of a
single stage radial compressor and axial turbine. During the course of designing the test
cell, there were plenty of sensors and other instrumentation devices that were integrated
to measure various parameters during the operation of the engine.
The engine was mounted on a spring-loaded slider platform. To measure the thrust
developed by the engine, a modified servomechanism was installed along with a
potentiometer to measure the resistance. The modified servo was linked to the platform
by the means of a connecting rod. This connecting rod was used to convert the linear
18
motion of the slider to the angular motion of the servo arm. The servo arm was
connected to the potentiometer. When the engine was in operation, the platform
experienced a linear movement due to the thrust developed by the engine. Due to the
linear movement, the servo arm rotates and a change in resistance is recorded by the
potentiometer. A correlation between the chance in resistance and the engine thrust was
deduced and thus the engine thrust was obtained. A pictorial representation of the
engine is shown in figure 2-1.
Figure 2-1 Arrangement of the MW-54 showing instrumentation
(Source: Leong et al, 2004)
Parameters like pressure, temperature and volume flow rates of air and fuel were
recorded using various instruments. A pressure gauge was installed to measure the case
pressure. In order to minimize resistance to the movement of the engine and minimize
any forces that would affect the thrust measurement, nylon tubes were used to connect
the pressure gauge and the pressure port on the engine. Exhaust gas temperature (EGT)
measurements were done using simple thermocouples placed in the exhaust cone, close
to the exhaust nozzle. According to the specifications of the engine given by the engine
19
manufacturer, the thermocouple was placed in such a way that only 2mm of the point of
measurement was protruding into the exhaust stream.
The engine speed was measured using a Hall effect sensor. A magnetic nut was installed
on the compressor. As the shaft rotated, the magnet developed a magnetic flux, which
was detected by the Hall effect sensor. This signal picked up by the sensor was then
communicated to the engine control unit (ECU) and also to the display device on the
test stand. Fuel flow rate was measured using an Infrared sensor and an impeller type
flow meter. A fuel pump is always incorporated on an engine to make sure there is
continuous flow of fuel passing into the engine. To monitor the flow rate of fuel, the
flow meter was mounted downstream of the fuel pump, before the fuel passed into the
engine. The flow meter was a turbine type meter so the fuel flow was measured as a
linear function of the rotational speed of the turbine in the flow meter, the rotational
speed being detected by an infra-red receiver that detected the passing turbine blades..
2.2.2. Ten years of experience with a small jet engine as a support for
education (Léonard et al, 2009)
According to Léonard et al (2009), jet propulsion is one of the key concepts in a
Masters level study in aerospace engineering. To provide an illustration for the students
of the concept of jet propulsion, the School of Mechanical and Aerospace engineering at
the University Of Liège, Belgium, procured a small jet engine. The motive to train
students on data measurement, acquisition and interpretation was kept in mind. The
engine procured had to meet the criteria of being able to be used in a laboratory
environment and not so small that there would be compromises on provision of
different sensors to measure the working parameters of the engine. The SR-30 mini
turbojet engine by Turbine Technologies Ltd was chosen. The SR-30 is a single spool
mini jet engine with a single stage radial compressor and an axial-flow turbine.
20
The test bench on which the engine was mounted underwent several modifications since
1997. The engine was taken away from the mounting legs of the old configuration and
was mounted on an Aluminum plate. This plate was suspended from the frame using
steel cables (figure 2-2). This was done to ensure the engine support place could move
freely in response to the thrust developed as cables provide better frictionless movement
than any other mechanism. In addition, flexible tubing was used to provide minimum
resistance to the movement of the engine. A Z-type load cell was employed to measure
the thrust developed. The load cell was mounted on the test floor, which would be
engaged when the suspended aluminum plate pressed against it (figure 2-3(a)). Before
the load cell could be used, a cable-pulley mechanism was used to calibrate the load
cell. A schematic arrangement of the test setup is shown in the figure 2-3(b).
Figure 2-2 Aluminum plate suspended using steel wires (Source: Léonard et al, 2009)
21
Figure 2-3 (a) Load cell mounted to the test floor (b) Completed arrangement of the SR-
30 (Source: Léonard et al, 2009)
As a requirement to perform the complete analysis of the engine, the measurement of
volume flow rate of air was essential. A calibrated nozzle replaced the bell-mouth of the
stock engine. This arrangement is shown in figure 2-4. The difference in the pressure at
the throat of the engine and the atmospheric pressure was calculated and hence the
volumetric flow rate of air was deduced. The technique used to measure the flow rate of
fuel was similar to that used in a diesel engine. A cavity of known volume fills up and
empties each time the fuel is supplied and this process repeats. A sensor was deployed
to sense this filling and emptying cavity. The sensor sends the signal to an electric
device and the frequency of the signal is converted to the fuel flow rate.
Figure 2-4 Arrangement of calibrated nozzle as an air flow meter measurement device
(Source: Léonard et al, 2009)
22
As a provision to control the engine using the airflow rate, a variable area nozzle was
installed. The default feature of the engine was the ability to control the power
developed by the engine using the fuel flow rate. The addition of this calibrated nozzle
meant that it was additional control parameter. This addition was done with an intention
to study the compressor characteristics.
On concluding the study, it was observed that the single-point method of measurement
(one-dimensional) was not an accurate way of obtaining the parameters. With the many
modifications done over a period of time, the apparatus was successful as an
educational tool because it provided a deep understanding of various scientific
phenomena.
2.2.3. Developing a jet engines experiment for the energy systems laboratory
(Pourmovahed et al, 2003)
With the same motive as seen in the previous papers (Léonard et al, 2009; Leong et al,
2004), a scaled down jet engine was installed in the energy systems laboratory of
Kettering University, USA. The engine installed was the SR-30 turbojet engine. Many
other authors (Léonard et al, 2009) have studied this engine and have published their
experiences. At the time of initial testing of the engine, it was found that the methods
used to measure thrust developed, fuel flow rate and engine speed were inadequate,
inaccurate and less reliable. Hence, the test rig was subjected to a dramatic makeover.
The structure on which the engine was mounted was easily distorted and affected the
thrust measurements significantly. The thrust measurement was further not reliable as
the load transducer used was outdated and inaccurate. There was no technique used to
monitor the airflow rate into the engine. The constraint on the engine support was
beyond the point of acceptance, which hampered the linear displacement of the engine
due to thrust, thus giving out poor thrust reading. The structure was such that the front
23
leg was supported firmly onto the test floor and the rear leg was not fixed. This resulted
in the engine not thrusting against the load transducer, thus giving out inaccurate thrust
reading. Moreover, because the rear leg was not bolted to the floor, the engine rotated
around the mounting bolts of the front leg, thus restraining it against engaging the load
cell. The load transducer used had a number of downfalls: it was a simple, strain-gauge
type of a load transducer which had no temperature compensation which means it was
never able to compensate for the change in system temperature while working in a high
temperature environment. The sensitivity was low, inaccurate and the load transducer
was mounted well below the centerline of the engine. All these factors put together, it
lead to a large margin of error which was unacceptable and needed amendment.
The engine supports were modified such that the engine was suspended using four
straps of steel shim stock. This ensured less resistance that meant the engine
experienced free movement and avoid any unlikely event of the engine twisting or
moving laterally. Complementing to the responsiveness, flexible tubing were used on
the pressure gauges connecting the pressure ports. An upmarket load transducer was
used which had high sensitivity and accuracy (up to 0.1lbF). Linear variation and
compensation to temperature were added advantages to the load transducer. The
structure operated so that it restrained the engine to move only axially against the load
cell, ensuring accurate readings of thrust. The method adopted by Léonard et al (2009)
was used to calibrate the load cell. A pictorial representation of the modified
arrangement is shown in figure 2-5.
24
Figure 2-5 Mounting arrangement of the SR-30 at Kettering University
(Source: Pourmovahed et al, 2003)
Relevant equipment to measure the flow rate of fuel and air were used. The flow rate of
fuel was recorded using a gravimetric approach. This method detected the change in
weight of fuel to calculate the flow rate. The old setup measured the engine speed by
converting the frequency to direct voltage. A direct frequency counter that returned the
voltage in both analog and digital forms replaced this. With the aim of studying the
emissions from the engine, a gas analyzer (Horiba MEXA 7100D) was used.
2.2.4. Micro-Jet test facility for Aerospace Propulsion Engineering Education
(Juste et al, n.d.)
The School of Aeronautics, Aerospace propulsion and Fluid Mechanics at the
Universidad Politecnica de Madrid installed a micro-jet engine as an educational tool to
enable students to understand the physical phenomena in the operation of a jet engine.
The heart of the apparatus was the Olympus HP micro-jet engine developed and
manufactured by AMT Netherlands. The Olympus HP, like any other mini-jet engines
used by Leong et al (2004) and Léonard et al (2009), has a single stage centrifugal
compressor, axial flow turbine, bell mouth inlet and a convergent exhaust nozzle.
25
The Engine Control Unit (ECU) is a key component present in the Olympus HP that is
useful in monitoring the working conditions. It assists in starting and stopping of the
engine makes the engine fail-safe and also includes basic telemetry software which
monitors several parameters like the exhaust gas temperature (EGT), engine speed. A
detailed technical specification of the Olympus HP can be found in the datasheet (AMT
Netherlands, 2009).
With an intention to study the performance of the engine, different parameters like flow
rates of air and fuel, thrust, pressure and temperatures at different stations of the engine
have to be measured. The ambient conditions of temperature and pressure are also
recorded. The engine was mounted on the test stand, which was bolted to the test floor.
A load cell was placed on a pedestal, which was bolted to the floor. The engine, when in
operation, was restrained axially by the load cell, which gave out the thrust reading.
Thermocouples and pressure probes were installed at each station to measure the
respective parameters. Pneumatic signals from the pressure probe were sent to their
respective pressure transducers to obtain the pressure reading at that station. It was
proposed to install sensors all over the circumference at each station, as the flow around
the circumference would be non-uniform. However, this circumferential arrangement of
sensors was not implemented, as multiple sensors would block the flow of the gases
(because the clearance between the combustion chamber and outer casing was found to
be 5.2mm). This interference of the gases would essentially drop the performance of the
engine, which was a demerit. As it is understood that the temperature at the combustor
exit is very high, two thermocouples placed laterally opposite to each other were used to
record the temperature at this station. A pictorial representation of the test setup and the
details of pressure, temperature sensors at each station is represented in figure 2-6(a)
and figure 2-6(b) respectively.
26
Figure 2-6 (a) Mounting arrangement of the Olympus HP (b) Schematic representation
of pressure and temperature probes at various stations (Source: Juste et al, n.d.)
The measurement of fuel flow rate was done using a turbine flow meter. Measuring the
engine speed was done by a magnetic pickup installed in the compressor, which created
a magnetic flux against a sensor during operation. These arrangements for measuring
flow rate of fuel and engine speed were used by Leong et al (2004). A calibrated nozzle
technique was proposed to measure the flow rate of air. However, this technique was
discarded citing a problem of the engine size. Alternatively, an indirect method of
calculating the airflow was executed by taking the temperature and pressure readings at
the exit of the exhaust nozzle following a calibration task.
2.2.5. Development of test stand for experimental investigation of chemical
and physical phenomena in Liquid Rocket Engine (Santos et al, 2011)
Through the National Plan of Space Activities (NPSA), the Brazilian Space Agency has
invested in a group of experts to carry out calculation, design and construction of Liquid
Rocket Engines (LREs). As a part of the agency’s space venture, the Institute of
Aeronautics and Space (IAE) tested the L5 jet engine. The L5 engine is a large-scale jet
engine running on Liquid Oxygen (LOX) and kerosene, used in the Brazilian Vehicle
Launcher for Satellites that develops a maximum thrust of 5000N. The thrust developed
27
by this engine was tested at the Liquid Propulsions Laboratory (LPL) located in São
José dos Compos.
The thrust testing apparatus consists of an interface support that allows fixing of the
engine onto it. The engine was fixed vertically so that the thrust force exerted is
upwards (exhaust is facing the surface of the earth). A cable-pulley mechanism was
used to calibrate the load cell used in the apparatus. A voltage proportional to the thrust
force was obtained when the engine restrained against the strain gauge, load cell. A
schematic arrangement and an AutoCAD drawing of the arrangement is shown in figure
2-7.
Figure 2-7 (a) Schematic arrangement of the L5 (b) AutoCAD drawing of the
arrangement (Source: Santos et al, 2011)
Although this setup was used on a large-scale engine, a similar test arrangement can be
developed based on the same grounds. However, the apparatus does not restrain the
twisting or movement of the engine in the lateral direction. Moreover, toppling of the
engine with respect to the horizontal plane is also possible.
28
2.2.6. Data Analysis and Performance Calibration of a small turbojet engine
(Bakalis and Stamatis, 2011)
Bakalis and Stamatis (2011) from the department of Mechanical engineering at the
University of Thessaly, Volos, Greece, developed a simulation model of a small turbojet
engine. The small turbojet engine used was the same as the one used by Juste et al (n.d.)
in Madrid. A detailed technical specification of the engine can be found in the datasheet
(AMT Netherlands, 2009). A number of discrepancies were observed mainly in the
temperature and pressure recording exercise. These measurement errors were mainly
because of the irregular flow-fields in the jet.
During the study of the engine, it was found that a temperature gradient was spread
across, all around the engine, which hampered the temperature measurements at
different stations. Because there was heat transfer within the stations, a difference
between the actual temperature and measured temperature was observed. At the turbine
exit, a drop in pressure was observed in the axial and radial directions, which made it
difficult for the pressure sensors to measure the pressure accurately. Taking into account
these inconsistencies, it has to be noted that the high temperature and pressure
variations have to be taken into account while evaluating the performance of the engine,
to avoid abnormal results.
Control of the Olympus HP turbojet engine is mainly executed by an ECU. Juste et al
(n.d.) explained the role of the ECU in the Olympus HP engine. The version of the
Olympus HP used in this study had extra measuring points for pressure and temperature
at each station so as to obtain accurate, all round measurements. A schematic
arrangement of the engine showing different stations and location of the sensors is
shown in figure 2-8.
29
Figure 2-8 Schematic arrangement of sensors around the Olympus HP
(Source: Bakalis & Stamatis, 2011)
All the measuring probes are installed at the mean radius, except for the static pressure
probes. The different sensors incorporated at each station are given in table 1.
Table 1 - Details on different sensors at stations (Source: Bakalis & Stamatis, 2011)
The ECU monitors the engine speed and EGT and maintains it within acceptable limits.
The EGT sensor is incorporated between the turbine exit and the nozzle entry (station 7)
and is linked to the ECU in order to control the engine. This means that maintaining the
30
EGT can be one of the ways of controlling the engine. A Z-type load cell of capacity
590N was used to measure the thrust.
Bakalis & Stamatis (2011) stated that in order to minimize or eliminate the errors, data
collection had to be done accurately, using a reliable method. Under steady-state
conditions, the engine was tested from idle speed to the maximum speed and various
results were presented. Pressures and temperatures at the compressor and turbine exit
were plotted with varying engine speed. Similarly, the turbine inlet temperature (TIT)
and the thrust exerted were plotted with engine speed and all these plots are shown in
figure 2-9.
Figure 2-9 (a) Pressure and temperature v/s engine speed at compressor exit (b) pressure
and temperature v/s engine speed at turbine exit (c) TIT and thrust v/s engine speed
(Source: Bakalis & Stamatis, 2011)
31
2.2.7. Design of a small jet engine test system for university education
(Tanabe et al, 2003)
Undergraduate students from the department of aerospace engineering at the Nihon
University, Japan, contributed in developing a small jet engine testing facility. The
apparatus was designed to impart an effective understanding of the working of a jet
engine. Unlike any other university, the students designed the engine in-house. This
allowed a better understanding on not only the operation of the engine, but the design
and manufacture of the engine components as well. The duration of the whole project
was well above one year. As a modification exercise, it was decided that an automotive
turbocharger would be used on the engine to provide the compression stage and the
students would be given the task to design the combustor and the nozzle. The project
was looked into by two sets of students: the first set looking at understanding the
automotive turbocharger, designing the components whereas the second set looked at
overall improvement of the design of the test facility. A schematic arrangement of the
test facility is shown in the figure 2-10.
Figure 2-10 Mounting arrangement of the custom small-scale jet engine at Nihon
University, Japan (Source: Tanabe et al, 2003)
32
As depicted, the engine is made to hang from the ceiling using four fine steel wires. The
principle of this arrangement is something similar to that, seen in Léonard et al (2009).
Because the engine is freely suspended, the movement of the engine during operation is
restrained minimally. Routing components like hoses and wires are also hung to avoid
resisting the engine movement. A load cell was fixed to a plate, which was suspended
from the ceiling. The engine, when in operation, would exert the thrust onto this load
cell, thus giving the thrust value. Airflow measurement was done using a flow meter,
which was installed in between the air filter and the turbocharger. The temperatures and
pressures at vital components like compressor, combustor and turbine were monitored
and controlled within their respective capacities. K-type and J-type thermocouples were
used to measure the temperature at various stations of the engine. Semi-conductor type
pressure sensors (COPAL PG-30-102R/103R) were used to record the pressures. The
engine speed was measured using a magnetic detector, which created a magnetic flux
during operation, and a sensor recorded the pulse to give out the engine speed-reading.
A piezoelectric sensor was used to measure the amount of vibrations in the system.
2.2.8. Operating experience with the Turbine Technologies SR-30 turbojet
engine test system (Callinan and Hikiss, 2002)
In 1999, the mechanical engineering department of the Loyola Marymount University
(LMU), USA, decided to acquire a scaled down turbojet engine to be used as an
experimental device for the undergraduate students in mechanical and aerospace
engineering. The engine was installed at the Thermal Sciences laboratory of the LMU.
The heart of the experimental setup was the SR-30 mini turbojet engine developed by
Turbine Technologies ltd. The SR-30 follows the usual design arrangement as many
other mini jet engines (Olympus HP, MW-54) i.e. a single stage centrifugal compressor
and axial turbine arrangement. A detailed specification has been given in the datasheet
33
(Turbine Technologies ltd, 2007). The MinilabTM
comprises of the SR-30 engine,
supporting equipment used for operation and control of the engine, a safety enclosure
within which the engine is housed, instrumentation to measure operational parameters
and a data acquisition system to collect, process the data.
As a part of the academic exercise, parameters like the specific thrust, component
efficiencies (combustor, turbine, and compressor), air-fuel ratio, thrust specific fuel
consumption and the specific thrust are calculated. To compare the thrust recorded
mechanically, an alternative thrust reading is calculated using the exhaust nozzle data.
The engine was installed as per the specifications provided by the manufacturer.
The instrumentation comprises of devices to mention the temperature, pressures, thrust
etc. K-type thermocouples are used to determine the temperature at different stations
(compressor inlet, combustor inlet, turbine inlet and exhaust inlet & outlet).
Piezoelectric transducers are employed to calculate the pressures at these different
stations. A 2-pole generator is used to measure the engine speed. Thrust is measured
using a strain gauge type load cell. The engine is mounted on two legs bolted to the test
floor. The load cell is mounted at a height half way through the centerline of the engine.
It is placed in such a way that the engine restrains against it during operation. A
pictorial representation of the arrangement is shown in figure 2-11. Figure 2-12 shows
the variation of thrust as a function of the engine speed. The data acquisition system
links the different sensors and assists in collecting and processing of the data. Digital
display devices are used to indicate different parameters like the oil pressure,
compressor air pressure, EGT, engine speed etc. A throttle lever is also provided to vary
the speed of the engine. A multi-meter is used to output the readings from the pressure
transducers of different stations, fuel flow rate and the readings from the load cell.
34
Thermocouple output is executed using an Omega model DP25-TC digital
thermocouple controller.
Figure 2-11 Standard mounting arrangement of the SR-30 at Loyola Marymount
University (Source: Callinan & Hikiss, 2002)
Figure 2-12 Thrust v/s engine speed obtained during experiments
(Source: Callinan & Hikiss, 2002)
With all the instrumentation in place, the engine was operated at different speeds. The
parameters obtained using the instrumentation were recorded and graphs were plotted as
a function of engine speed. Typical results obtained in the test have been tabulated in
table 2. In the table, nozzle efficiency reads 211%, which is an unrealistic figure. This
inconsistency is due to the incorrect temperature reading at the turbine inlet.
35
Table 2 - Results obtained for the SR-30 at LMU (Source: Callinan & Hikiss, 2002)
2.2.9. Characterising the performance of an SR-30 turbojet engine
(Witkowski et al, 2003)
The SR-30 small-scale turbojet engine is being used as an important educational tool in
many universities across the world. As discussed earlier, the SR-30 follows the
conventional configuration of a small-scale turbojet engine i.e. a single stage centrifugal
compressor and an axial turbine. For the students to record respective parameters and
conduct a thermodynamic study, temperature and pressure sensors have been installed
at each station of the engine. The limitation of the study is that the analysis carried out
is one-dimensional and hence the results that were obtained would not look practical.
At the inlet nozzle, the pressure was calculated using the pressure differential between
the pressure of the flow entering the engine and the atmospheric pressure. As the SR-30
has a bell mouth shaped inlet nozzle, it serves in creating a uniform velocity profile.
Using this uniform velocity profile as an assumption, the mass flow rate of air entering
the engine could be calculated. Flexibility in the installed probes meant that the operator
had the liberty to reposition the sensors. The reason behind that was to study the
difference in the calculations performed by the students when the positions of the
sensors were switched. During the starting of the engine, thermal transients were
36
observed within the engine. For these transients to reach a steady state, the engine had
to be kept on idle before any analysis was done. In order to tackle this problem of
thermal transients, three different types of starting (cold, medium, hot) was done on the
SR-30 and the temperature at the compressor exit was recorded.
The temperature at the compressor exit was measured using two temperature probes.
The first probe was fixed, facing the exhaust nozzle plane and the second probe was
allowed to traverse along a defined path to obtain a detailed profile measurement of the
exhaust cone. The temperature at the compressor exit was found to vary around the
circumference. To overcome this issue, the students were asked to integrate the
temperature over the inner wall to the outer wall. An alternative method was to place
thermocouples all around the circumference and take the average value. A total of three
different methods were adopted to measure the temperature at the compressor exit. The
three methods were integrated method, average method and the midpoint method. The
results using the three methods have been presented in table 3. In measuring the
temperature at the combustion chamber, a temperature difference of about 50-70
degrees Celsius was observed between the outer wall of the combustion chamber and
the inner wall of the casing (distance of 10mm). The pressure reading however, hardly
varied. The results obtained from the experiment are presented in table 4.
Table 3 - Temperature at the compressor exit calculated using three different methods
(Source: Witkowski et al, 2003)
37
Table 4 - Results obtained on the SR-30 at the University of Minnesota
(Source: Witkowski et al, 2003)
2.3. Summary
To give a brief insight of the literature, the findings from each paper have been
tabulated as shown in table 5.
38
Year/Author University Engine
Mounting
Method
Thrust
Measurement
Instrumentation
Leong et al,
2004
Western
Michigan
University,
USA
MW-54,
Wren
Turbines
Ltd.
Spring-
loaded slider
platform
Modified
servomechanis
m,
potentiometer
Hall effect sensor
for engine speed,
impeller type flow
meter for fuel
flow rate
Léonard et al,
2009
University
Of Liège,
Belgium
SR-30,
Turbine
Technolo
gies Ltd.
Mounted on
Aluminium
plate,
suspended
using steel
cables
Load cell
mounted to the
test floor
Calibrated nozzle
for air-flow
measurement,
emptying cavity
type fuel flow
measurement
Pourmovahed
et al, 2003
Kettering
University,
USA
SR-30,
Turbine
Technolo
gies Ltd.
Suspended
using four
straps of
steel shim
stock
Load cell
mounted on the
test floor
Gas analyser, air
flow
measurement
Juste et al,
n.d.
Universidad
Politecnica
de Madrid,
Spain
Olympus
HP,
AMT
Netherlan
ds
Mounted on
cantilever
beam, bolted
to test floor
Load cell
mounted on a
pedestal
ECU,
Circumferential
placement of
sensors, turbine
flow-meter for
fuel, magnetic
pickup sensor for
speed
Bakalis and
Stamatis,
2011
University
of Thessaly,
Greece
Olympus
HP,
AMT
Netherlan
ds
Not
mentioned
Z-type load cell
ECU,
Circumferential
placement of
sensors
Tanabe et al,
2003
Nihon
University,
Japan
Self-built
Suspended
from the
ceiling using
four steel
wires
Load cell was
suspended from
the ceiling
Turbine flow-
meter for fuel,
magnetic detector
for engine speed,
piezoelectric
sensor for
vibrations
Callinan and
Hikiss, 2002
Loyola
Marymount
University,
USA
SR-30,
Turbine
Technolo
gies Ltd.
Mounted on
two legs
bolted to test
floor
Load cell
placed on a
pedestal, close
to the centreline
of exhaust
2-pole generator
for engine speed,
display devices
for
instrumentation
Witkowski et
al, 2003
University
of
Minnesota,
USA
SR-30,
Turbine
Technolo
gies Ltd.
Not
mentioned
Load cell
mounted on the
test floor
Pressure and
temperature
sensors
Table 5 - Summary of literature review
39
2.4. Conclusion
So far, the literature has given an account of the various mounting methods of small-
scale jet engines, different instrumentation used and their role in studying the
performance of the engine. Looking at the different mounting techniques, the movement
of the engine has to be restrained minimally so that the accuracy of the thrust reading is
enhanced. As there are no mechanical parts present in the suspended way of mounting,
this would be an ideal way to achieve a linear motion with minimum resistance. These
designs were adopted by Léonard et al (2009) & Tanabe et al (2003). The literature also
describes the different techniques adapted to record parameters like temperature,
pressure, and flow rates of air & fuel. Apart from these basic parameters, Pourmovahed
et al. (2003) used a gas analyzer to study the emissions from the engine.
On a concluding note, the literature review forms a foundation to the succeeding
research in this topic of improvisations to the small-scale jet engine experiment at the
University of Manchester. With the help of the literature, the demerits were identified
and improvisations were recommended. Furthermore, new techniques of measuring
necessary parameters are discussed.
40
Chapter 3
DESIGN METHODOLOGY & MODELING
3.1. Background
The basis of this chapter is for the reader to understand the structure adopted, in
carrying out the research. The existing model (shown in Turbine Technologies ltd,
2007) was studied briefly and the downfalls in the model were many. The mounting
structure had to be completely redesigned and the instrumentation had to be replaced as
well. As an ideal way of designing, multiple models were created and studied
thoroughly using SolidWorks 2012. The study involved two basic steps – feasibility
study and a simulation study. Feasibility study involved a basic study, which was done
by visually analyzing the model, discussing the ease of maintenance, and safety factors
in the design. Simulation study involved a rigorous study of the model using a Finite
Element Analysis (FEA) method. The results gathered from the FEA were then
compared and a conclusion was reached. Additional instrumentation, which could be
helpful in executing a detailed analysis of the engine, was suggested.
3.1.1. Finite Element Analysis
In the modern world, a rapid development has been observed in the field of numerical
analysis and simulation. Numerical simulation has emerged as a key technology in the
scientific and industrial applications (Roylance, 2011). One such numerical simulation
method used to study physical structures is called Finite Element Method (FEM) or
Finite Element Analysis (FEA). FEM involves numerically breaking the structure into a
large number of small entities called finite elements. These elements take different
shapes and sizes in order to match the physical geometry. This method is used to study
complex shapes where conventional methods like matrix displacement methods cannot
41
be implemented (Ross, 1998). Vuong (2012) regarded the finite element method as one
of the most prominent methods to solve partial differential equations. FEA can be used
to solve many complex shapes with lower computational time than other methods.
However, as the problem gets more and more realistic, the computational time may go
up or it may be difficult to obtain a solution (Vuong, 2012). Apart from this, any error
in inputs from the user may lead to incorrect solutions, which the designer may
overlook (Roylance, 2011).
3.1.2. Design Criterion – Distortion Energy Density Criterion
There are a number of design criteria that can be used in the finite element study. In this
study, the Distortion Energy Density Criterion or Von-Mises Criterion has been used as
the design criterion. Boresi & Schmidt (2003) stated this theory as the occurrence of
yielding of a material when the distortional strain-energy density being equal to that of a
material under uniaxial compression (or tension). Total strain energy (Uo) can be split
into 2 parts – strain energy causing volumetric change (Uv) and strain energy causing
distortion (UD) (Boresi & Schmidt, 2003). Mathematically, this can be expressed as,
( ) ( ) ( ) ( )
The first expression on the right hand side denotes the strain energy causing the change
in volume and the second expression denotes the distortional strain energy.
3.1.3. About the software
The study of stresses on the structures was done using the SolidWorks 2012, a modeling
and simulation software developed by Dassault Systèmes, France. SolidWorks 2012 is
feature-packed software used popularly for three-dimensional modeling of components
as well as assembly. The software also allows the user to execute a finite element study
42
of the modeled components/assembly. It also allows the user to choose the type of study
like static, thermal, nonlinear, buckling, fatigue etc. (Help.solidworks.com, n.d.).
The static study of the components involves a basic study of calculating the
displacements, stresses, strains and resultant forces when the component/assembly is
subjected to a load (Help.solidworks.com, n.d.). SolidWorks simulation incorporates
two types of finite element solvers namely FFEplus and the direct sparse solver.
FFEplus is the iterative type of solver, which is used primarily as it is a faster solver and
can be used in studying non-linear problems. The direct sparse solver is used in the case
of multi-area contact problems (Help.solidworks.com, n.d.).
3.2. Selection of Material for the structure
Selecting the material of the structure plays a very important role in the mechanical
design. The material chosen should acquire various characteristics before it can be
considered for the design exercise. Availability, machinability, low-cost, lightweight,
high yield strength, minimum thermal conductivity etc. are some of these
characteristics. Two materials were chosen for analysis – AISI 1020 steel (Cold rolled)
and Aluminum 1060 Alloy. Properties of these two materials are listed in table 6.
Material Properties
Name AISI 1020 Steel, cold rolled Aluminium 1060 Alloy
Yield Strength (N/m2
) 3.5 x 108
2.75 x 107
Tensile Strength (N/m2
) 4.2 x 108
6.893 x 107
Elastic Modulus (N/m2
) 2.05 x 1011
6.9 x 1010
Poisson's ratio 0.29 0.33
Density (kg/m3
) 7870 2700
Shear Modulus (N/m2
) 8 x 1010
2.7 x 1010
Thermal Coefficient (/K) 1.17 x 10-5
2.4 x 10-5
Table 6 - Material properties (Source: SolidWorks 2012 material library)
43
3.3. Modeling
Before progressing to the improvements suggested, a brief overview of the existing
model is discussed. The engine in question was the SR-30 by Turbine Technologies
Ltd. The existing model of the structure (shown in Turbine Technologies ltd, 2007) was
modeled and studied using SolidWorks. A simulation study on this model revealed that
the application of thrust on the structure would deform the structure by an approximate
1mm. The engine was mounted only on one leg, which resulted in improper thrusting of
the engine against the load cell. As a result, the thrust reading would not be accurate.
This meant the replacement structure had to allow the horizontal movement of the
engine so that the load cell could be engaged.
A university edition of the Olympus HP was procured from AMT Netherlands and
replaced the SR-30. The specification of this engine is given in the datasheet (AMT
Netherlands, 2009). A range of designs is presented in this section to allow mounting of
the Olympus. The objective of the design was to make sure there was unobstructed
movement of the engine so as to produce accurate thrust readings and incorporate
instrumentation to make the experimental setup more practical and easier to use.
Before the modeling phase was started, rough dimensions of the test floor were
recorded. The engine had to be positioned in such a way that the centerline of the jet
engine exhaust coincided with the centerline of the exhaust duct in the laboratory
ventilation/extraction system. The centerline of the exhaust was 310mm from the floor
of the existing test frame. Therefore, the structures were to be designed such that the
centerline of the jet engine exhaust was located 310mm above the floor level.
The modeling phase followed an orderly sequence of steps, which was then analyzed
using the simulation feature in SolidWorks 2012. The steps are as follows:
1) Individual parts are modelled in 3-dimension form.
44
2) An assembly of the structure is built using the individual parts.
3) Any restrictions to the moving parts are applied to make the model realistic.
4) A simulation study is created (static study) by defining the sensor type, which is
used to monitor the quantities of results in a part of a body or the entire body.
The design criteria are also chosen as a property of the sensor
(Help.solidworks.com, n.d.)
5) On defining the sensor type, the static study is further defined by fixtures and
the loads acting on the body. Different types of fixtures can be chosen –
Cantilever type, roller supports etc. SolidWorks also allows the user to define
the type of loading (Force, Torque, and Pressure etc.)
6) In the simulation of an assembly, the user defines all the connections. This
feature assists in the execution of the simulation and also calculates the reaction
forces at each of the connectors. Springs, bolts, pins, links, welds and bearings
are few of the connectors that can be used in the CAD package.
7) Once the connectors are defined, the model is ready to be executed. Execution of
the model breaks the model into very small, finite elements, which are further
analysed.
8) Plots of Von Mises stress in the model, strain and displacement of the model are
obtained which can be used for further analysis. This step is discussed in the
next chapter. An optional plot of factor of safety in the design can also be
obtained.
Keeping these steps in mind, multiple designs were created for the mounting structure.
Following is a detail on these different mounting methods conceptualized to mount the
Olympus HP.
45
3.3.1. Design 1
The first mounting technique resembles the method used by Léonard et al (2009) at the
University of Liège. A lower base plate is suspended using four, high tensile strength
wires which are connected to a frame secured to the test floor. A single block of metal
acts as the leg, which is bolted to the aluminum plate on which there is an upper base
plate mounted. Four pillars of about 110mm length are fixed to the upper base plate.
The engine is mounted on these four pillars and secured with 4mm bolts. Essentially,
the legs, upper base plate and the pillars rest on the lower base plate, which is
suspended from the frame using steel cables. Figure 3-1 illustrates the first alternative.
Figure 3-1 (a) Exploded view of design 1 (b) Schematic arrangement of design 1
When the engine is in operation, the thrust exerted is acted upon the entire assembly
mounted on the lower base plate, suspended from the frame. This thrust results in a
horizontal movement of the lower base plate over a very small distance. The wire
suspension system would mean that the base plate would start to rise if it was free to
move. A strain gauge type load cell assembly mounted on the test floor stops this
movement and the deformation in the cell is converted to the thrust reading.
46
3.3.2. Design 2
In order to make the assembly lighter, the arrangement in the above design was altered.
The weight reduction technique meant the single leg was replaced with two bent, sheet
metal legs that were bolted to the lower base plate. Because of this alteration, the
surface area of contact was spread across the width of the lower base plate. Taking into
account the basic principle of stress in a body, increasing surface area would mean that
the stress in the body goes down. Figure 3-2 depicts the second alternative of the
design.
Figure 3-2 (a) Exploded view of design 2 (b) Schematic arrangement of design 2
In the case of design 1 and 2, a Bowden cable arrangement can be incorporated to adjust
the length of the cable and maintain horizontality of the lower base plate. The width of
the lower base plate is almost equal to the gap between the legs of the frame. A small
tolerance (about 0.5 to 1mm) should be given between the lower base plate and the legs
of the frame. This restricts the lower base plate to move only in the axial (thrust)
direction, ruling out the possibility of twisting or lifting of the plate when the engine is
working. The lower base plates were suspended at 80mm from the test floor and the gap
47
under them was used to concealing electrical wires, the ECU and other small auxiliary
equipment as well as providing a thermal shield from the radiated heat from the exhaust.
3.3.3. Design 3
The third option incorporated a linear rail-slide mechanism to allow linear movement of
the engine due to thrust. The assembly comprises of a cantilever beam secured to the
test floor. A rail is attached to this cantilever beam and a slider is allowed to slide on
this rail. The movement of the slider is restricted to about 10-15mm so as to avoid
shifting of the weight. Physically, providing a “stopper” which terminates the motion at
the required point can do this. Alternatively, a load cell mounted on a pedestal can stop
this. The load cell doubles up as a stopper and a thrust-measuring device. In the
SolidWorks model however, this restriction of the movement is given by defining a
length by which the slider moves. Hence, we do not see a physical stopper in the figure
3-3, which depicts the third design in question. The slider carries an upper base plate,
which has four pillars, mounted on it. These pillars act as legs on which the engine sits.
Figure 3-3 (a) Exploded view of design 3 (b) Schematic arrangement of design 3
48
3.3.4. Design 4
The fourth and final model is very similar to the third model discussed in the previous
section. The only difference is that this model has two cantilever beams mounted on to
the test floor. Likewise, there are two rail-slide mechanisms used – one on each beam.
This is mainly done for better weight distribution of the engine when it is mounted. The
upper base plate and the pillars are exactly the same as seen in the previous design
(design 3). Figure 3-4 depicts the fourth design.
Figure 3-4 (a) Exploded view of design 4 (b) Schematic arrangement of design 4
3.4. Input parameters for Simulation
Before the finite element method can be carried out, the assembly is subjected to a
procedure of inputting different parameters, which are essential. The sequence of this
input has been discussed earlier in section 3.3.
3.4.1. Definition of Material
This is the primary step in the procedure of analysis. The material for the assembly is
defined in this step. This assigns the properties of the material. Properties like yield
49
strength, tensile strength etc. is defined. The properties and selection criteria of the
material have been discussed in section 3.2.
3.4.2. Fixture & Loading details
As a secondary requirement for the analysis, the fixtures and loading on the assembly is
defined. Figure 3-5 shows fixture and loading details for all the design options in
consideration. The green arrows denote the fixture. The fixture has been defined as the
top of the lower base plate because it is suspended from the frame and the linear
movement of the plate is very small (as it restrains against the load cell). This small
movement is considered negligible in the analysis; hence the top of the lower base plate
is treated fixed. In designs 3 & 4, the lower base plate can be treated as the test floor i.e.
fixed from the bottom.
Figure 3-5 Fixture and loading details on (a) Design 1 (b) Design 2 (c) Design 3 (d)
Design 4
Loading on the material is defined by selecting the faces on which the load acts and
entering the magnitude of the load (force). A load of 230N is applied on the faces, as
50
this is the maximum thrust developed by the Olympus HP (AMT Netherlands, 2009).
Purple arrows denote the faces subjected to load.
3.5. Summary
This chapter focuses on the preliminary part of the research such as the methodology
adapted in executing the research, an overview of the software used, method adopted in
selection of material for the structure and Computer aided modeling. This chapter also
emphasizes on the design aspect of the research such as the theory behind the analysis
and the method of analysis. A brief insight on the arrangement of different models
followed by the input parameters for the simulation is outline in this chapter.
The next part of the research gives detailed information on the type of simulation
carried out, the input data on the simulation study and the behavior of these models
under the action of loads. Results are presented for each model and discussed. Issues
pertaining to maintenance, safety and practicality of the structure are also discussed.
51
Chapter 4
RESULTS AND DISCUSSION
The previous chapter briefly focused on the theories involved in design, the
methodology of design and also the four models that were developed for analysis. In
this chapter, an elaborated process of the simulation and design is presented which is
followed by the results of these simulations. Before showing the results, the
arrangements for the measurement of thrust are discussed.
4.1. Thrust Measurement
Measurement of thrust is a vital step in analyzing the performance of any jet engine – be
it small scaled or the actual aircraft engine. The thrust measurement assembly in the old
setup was not reliable enough; as a result giving inaccurate thrust values. Using a strain-
gauge type load cell is the simplest and most accurate way of obtaining the thrust
developed by the engine (Hafizah et al, 2012). The arrangement of the load cell depends
on the arrangement of the structure. In the case of the first two designs (design 1 and 2),
it is proposed that the load cell be mounted on the test floor. This allows the suspended
lower base plate to press against the load cell, thus giving the thrust output.
In the case of design 3 & 4, the upper base plate is the moving part, which carries the
load of the engine. Since the upper base plate is at a height of about 215mm from the
test floor, the load cell may have to be mounted on a pedestal or a cantilever for the
upper base plate to act on it. This arrangement allows the load cell to be closer to the
centerline of the engine, which is similar to the arrangement used by Callinan & Hikiss
(2002).
52
4.2. Simulation results
As the main objective of the research, which is to design a suitable test rig for the
Olympus HP small-scale jet engine, the results of the finite element analysis of the four
designs are presented in this section. On each design, two studies are carried out – first
study being AISI 1020 Steel as the material and the second study with Aluminum 1060
alloy as the material. With the loads and fixtures in place, the program is executed. The
assembly is broken into finite elements, thus generating a meshed model.
The results are generated in the form of plots showing the Von-Mises stress,
displacement and strain in the model. The maximum and minimum points of these
parameters also form a part of the result. The results for the first half of the study i.e.
with material AISI 1020 steel are given below.
Figure 4-1 Von-Mises stresses in (a) Design 1 (b) Design 2 (c) Design 3 (d) Design 4 –
AISI 1020 Steel material
53
Figure 4-2 Displacements in (a) Design 1 (b) Design 2 (c) Design 3 (d) Design 4 – AISI
1020 Steel Material
Figure 4-3 Strains in (a) Design 1 (b) Design 2 (c) Design 3 (d) Design 4 – AISI 1020
Steel material
54
The same procedure is now repeated for all the four cases with using Aluminum 1060
alloy as the material for the structure. The density of aluminum is about 35% of that of
steel (table 6) hence, aluminum is a lighter material compared to steel, which makes it
easy from the handling point of view. Machinability is also an advantage as aluminum
is much softer than steel (Boresi & Schmidt, 2003). Adding up all the plus points,
aluminum makes an ideal material to be used for the structure. Having completed the
analysis with aluminum as the material, the results are obtained. Although the yield
strength of aluminum is much lower than that of steel, the Von-Mises stress in all the
four designs is much lower than the yield strength of aluminum. This is shown in figure
4-4. Displacement and strain are also well within the allowable region as they are of the
order of 10-3
mm and 10-5
respectively. The displacements and strains in the four
designs are shown in figure 4-5 and 4-6 respectively.
Figure 4-4 Von-Mises stress in (a) Design 1 (b) Design 2 (c) Design 3 (d) Design 4 –
Aluminum 1060 Alloy
55
Figure 4-5 Displacements in (a) Design 1 (b) Design 2 (c) Design 3 (d) Design 4 –
Aluminum 1060 Alloy
Figure 4-6 Strains in (a) Design 1 (b) Design 2 (c) Design 3 (d) Design 4 – Aluminum
1060 Alloy
56
The results obtained in both the studies can be summarized and tabulated as shown in
table 7.
AISI 1020 Steel Aluminium 1060 Alloy
Max
Von-
Mises
stress
(N/m2
)
Max
Displacement
(mm)
Max
Strain
Max
Von-
Mises
stress
(N/m2
)
Max
Displacement
(mm)
Max
Strain
Design 1 798844 0.00368 2.31x10-6
829625 0.00464 7.35x10-6
Design 2 3460000 0.0032 1.13x10-5
3455000 0.00747 3.46x10-5
Design 3 2101340 0.01513 5.15x10-6
2034200 0.03125 1.55x10-5
Design 4 1785690 0.00297 4.76x10-6
1724180 0.00832 1.47x10-5
Table 7 Summary of results
With the given material combination and the loading, fixture details, all the designs are
feasible to be adopted as the structure for mounting the Olympus. This may be the
primary requirement, if not the only one. Apart from the capability of the structure to
take the load and restrict deformation, factors like maintenance, reliability, and safety
also come under the spotlight. This is discussed as a separate section.
4.3. Other Parameters
Periodic maintenance is a must for any mechanical structure, which is subjected to a
rugged atmosphere. Here, the structure is often exposed to temperature and fatigue
loading. As the engine would be operated often, it could be subjected to fatigue loading.
Subjecting an object to repeated load, over a period of time, causes fatigue failure.
According to Campbell (2008), fatigue is caused by three factors – high tensile strength,
high frequency of loading and large variation in the applied load. However, the loading
in our structure does not satisfy any of these three factors. This is because the frequency
of load application is not large enough, variation of the load is marginal and the Von-
57
Mises stress induced in the assemblies is small compared to the tensile strength. Thus,
failure due to fatigue can be ruled out.
In an inevitable circumstance of having to dismantle the setup, it has to be easy and
convenient for the operator to solve the problem and get the setup back into use. As
seen in design 1 and 2, the Bowden cable with locking nut not only maintains
horizontality, but it is also easier to mount/dismount the lower base plate. If the engine
has to be dismounted off the lower base plate, the Bowden cable can be used to lower
the base plate and thus making it easier to access the mechanical connections.
The height of the pillars has been restricted to 110mm. This is to avoid distortion of the
pillar due to torque. We know that torque is a product of force and the perpendicular
distance. Therefore, as the height of the pillar increases, the magnitude of torque
increases. The height of the frame has been restricted to 110mm to avoid the risk of the
frame heating up due to the radiation from the exhaust of the engine. As a precautionary
measure, a thermocouple may be installed at the end of the frame to monitor the
temperature at the back end of the frame.
In the case of design 3 and 4, frequent maintenance would be a concern. As these
designs involve the linear slider mechanism, it may need frequent lubrication to
maintain minimum friction and hence a smoother linear motion. Since the linear motion
is restricted to a very small length, the assembly will have to be dismantled when the
rail needs lubrication.
58
Chapter 5
INSTRUMENTATION IMPROVEMENTS
The previous chapter focused on different designs and their behavior upon the action of
load. A brief insight was given on the maintenance and safety of these designs. This
chapter gives an insight on the possible improvements that can be executed from the
instrumentation point of view, which is the second-half of the objective. From the
beginning, feedback and control has been an essential tool for a jet engine (Spang III &
Brown, 1999). As it is a complex system operating at high temperature and pressure
conditions, jet engines require close monitoring to ensure safe and cost-effective
operation (May et al, n.d.). With the purpose of continuously monitoring the physical
state, jet engines are equipped with computers that help in controlling their operation.
The Olympus HP comes with an inbuilt ECU, which monitors the EGT and the engine
speed. The ECU makes sure that the engine does not exceed the engine speed or EGT
beyond a prefixed point (AMT Netherlands, 2008). A detailed connection diagram
linking the ECU with the engine can be found in the user manual of Olympus HP (AMT
Netherlands, 2008). The university edition of Olympus HP comes with extra measuring
points allowing the operator to measure the parameters extensively and facilitates a
detailed study of the engine performance. These extra measuring points cover static and
total parameters (temperature, pressure) at appropriate points in the engine to best
represent the thermodynamic cycle (Amtjets.com, 2011). With improper shielding of
the thermocouples, the temperature values may be affected and hence the calculation of
efficiency values of the turbine and compressor may not be accurate (Callinan & Hikiss,
2002). Employing multiple sensors placed along the circumference at critical stations
like the turbine inlet and the exit of the turbine could be a solution to overcome this
problem (Bakalis & Stamatis, 2011).
59
Apart from these control and measurement features, third party elements can be
incorporated and linked to the data acquisition system to obtain different parameters.
Thrust measurement has already been discussed in the earlier section (section 4.1.). Fuel
flow rate can be measured using different ways. The most commonly used method is by
using an impeller, or turbine, type flow meter, mounted in between the engine inlet and
the fuel pump. This is a reasonably accurate way of measuring the fuel flow rate, as it is
accurate to 1%. In this method however, the impeller of the flow meter may wear out
over a period of time and the viscosity of the fuel also matters in the operation (Walsh
& Fletcher, 2008). Alternatively, a visual way of recording the fuel-flow rate can be
implemented by using a stop clock and a glass bottle. However, this method is less
accurate as the reading is manually recorded.
In the case of small-scale jet engines, the vibration is less in magnitude. Nevertheless,
from the safety point of view, techniques may be adopted to measure the vibration of
the engine setup. Piezoelectric accelerometers can be used for measuring vibrations.
These devices are small, rugged, convenient and suitable for use at high temperature
and pressure conditions (May et al, n.d.). Vibrations may also be continuously
monitored using a vibration transmitter mounted on the top of the engine casing. An
electromagnetic transducer transmits a signal to the indicator and gives the magnitude
of the vibration. A warning lamp may also be used for added safety (Royce Plc, 1986).
Tanabe et al (2003) demonstrated the use of piezoelectric sensors to measure the
vibrations in a small-scale jet engine.
The EGT is a very important parameter in the operation of a jet engine. As mentioned
earlier, the ECU does the job of maintaining the EGT within permissible limits, by
using it as a feedback signal to control the engine. Although the ECU in the Olympus
has a fail-safe feature, an automatic gas temperature control system may be provided to
60
keep the EGT within limits (Royce Plc, 1986). Flow-rate of air may need an accurate
measurement method. Installing a calibrated nozzle at the inlet can satisfy this. Exhaust
gas temperature can be measured by placing a fixed probe close to the exhaust nozzle. It
has to be made sure that the probe does not protrude so much that it blocks the flow of
exhaust gases. A secondary probe that is traversable along the path of the exhaust can
be used to take profile measurements of the exhaust cone (Witkowski et al, 2003). A
thermal imaging camera can also be installed to study the exhaust gases. The profile
measurements can be recorded easily with the thermal imaging camera as compared to
the traversing probe technique. The price of a thermal imaging camera however, would
be a major drawback.
Pressure sensors may be installed circumferentially to record the static pressure at the
inlet. Airflow can then be calculated by recording the pressure difference. Léonard et al
(2009) adopted this method at the University of Liège, Belgium. Alternatively, the
market offers a variety of equipment that can be used to measure the flow rate of air. A
Sierra 780S Flat-Trak Mass Air Meter was used by Pourmovahed et al. (2003) to
measure the airflow rate on the SR-30 at the Kettering University, USA. Incorporating
such equipment may not be economical, but can give accurate readings.
Measuring the engine speed is also a very important step in analyzing the performance
of the engine. The literature already has many different methods of measuring the
engine speed. The most common and accurate method would be the use of a Hall effect
sensor and a magnetic pickup. This method is suitable for small-jet engines and has
been incorporated by Tanabe et al (2003); Juste et al. (n.d.) and Leong et al (2004). An
alternative to this method would be the use of a small generator driven by the engine,
which indicates the engine speed through a visual indicator (Royce Plc, 1986). The
second method however, would require major alterations to the engine which can be a
61
tedious job and expensive. Also anything that is powered by the engine would affect the
engine and interfere with any set points within the ECU to control the engine operation.
Since the engine speed is also a parameter, which cannot exceed a permissible limit, a
warning lamp may be provided for the same (Royce Plc, 1986). The addition of a fuel
gauge to measure the level of fuel in the tank may be a useful addition. A gas analyzer
can be implemented to study the emissions from the engine.
A virtual simulation analysis of the rotating components can be studied using
commercially available CAD software. Linking the data acquisition system to the
simulation software would be handy in importing the data. Leong et al (2004) used a
similar technique to study the performance of the engine and compare it to the results
from the manufacturer. Real-time simulation can be used to compute the performance of
the engine based on the inputs from the data acquisition system. These results may be
compared to the theoretical results obtained by the students or the results from the
manufacturer of the engine to verify the accuracy in results.
62
Chapter 6
CONCLUSION AND SCOPE FOR FUTURE WORK
6.1. Conclusion
Looking back at the literature in this we can understand that there are several ways of
mounting the small-scale jet engines and there are plenty of techniques to measure
different parameters. One such small-scale jet engine along with a test bench which has
adequate facilities to measure different parameters and using a data acquisition system
would be an ideal platform for any researcher to get acquainted with the theory of jet
propulsion and study the performance a jet engine (Léonard et al, 2009). With the
procurement of an Olympus HP E-start engine for the engine test cell, students at the
School of Mechanical, Aerospace and Civil Engineering are sure to find it easier to
understand the basics behind jet propulsion.
The literature mainly focuses on the experiments carried out in different academic
institutions across the globe. No part of the literature discusses primarily on the design
of the test rig for small-scale jet engines. As mentioned in section 1.3, the primary
objective of the research was to look at the literature and design an appropriate test rig
to mount the Olympus HP jet engine. The old setup had problems with measuring the
thrust, as the engine was unable to transfer the load onto the load cell. This was because
of distortion in the mounting structure, making it less responsive to the thrust
developed. Designs were developed based on the literature and also some knowledge on
the requirements for a useful design. These designs were studied using a finite element
package and the solutions were drawn out. Design 2 was found to be the optimum of
the four designs because of the engine being mounted on a suspended lower base plate
arrangement, which meant it was responsive to the thrust generated. The stresses
generated in this arrangement were within the acceptable limits (Figure 4-4). The use of
63
two sheet metal legs as against one block (as in design 1) allows better weight
distribution. This design is a modified version of the structure used by Léonard et al
(2009). From the instrumentation point of view, the Olympus HP comes with prefixed
extra measurement points for pressure and temperature, mainly designed for usage in
universities as an educational tool (Amtjets.com, 2011). We have looked at various
ways of measuring parameters like flow rates of air and fuel, engine speed and other
parameters like vibration in the equipment. Studying the engine would give a clear idea
about the limitations involved in assumptions and approximations made in analytical
performance (Leong et al, 2004). As used by Bakalis & Stamatis (2011), placing
circumferential temperature sensors can be considered to get an average temperature
reading at the station and also to plot a profile of the temperatures along the
circumference.
6.2. Scope for future work
Jet propulsion education being a fundamental topic in aerospace education, the small-
scale jet engine is being used as an important experimental tool by many universities
across the globe. The above study can be carried forward to optimize the design in
terms of minimizing the plate thickness to reduce the weight of the entire structure. To
get a visual idea of the operation of the engine, a CFD study can be carried out on the
whole engine or on specific components like the compressor, combustor and the
turbine. This study has considered the surroundings of the engine to be in ambient
condition. However, this is not the case in real. Heat may be transferred to the mounting
structure through conduction, convection or by radiation. Thermal stresses induced in
the structure may be studied by placing thermocouples around the test rig to record the
temperature due to the heat transfer mechanisms. Additional test rigs may be developed
to study the gas concentrations at different points around the engine and relate it to the
64
local temperatures. As a long-term development, forced airflow around the engine could
be used to simulate the behavior of the jet engine during flight.
65
References:
AMT Netherlands. 2008. Manual - Olympus HP E-Start. [report] Helmond: AMT
Netherlands.
AMT Netherlands. 2009. Olympus HP Gas turbine - Specification sheet. [report]
Helmond: AMT Netherlands.
Amtjets.com. 2011. AMT Netherlands Olympus HP. [online] Available at:
http://www.amtjets.com/OlympusHPuniversity.php [Accessed: 07 July 2013].
Bakalis, D. and Stamatis, A. 2011. Data Analysis and performance model calibration of
a small turbojet engine. Proceedings of the Institution of Mechanical Engineers,
Part G: Journal of Aerospace Engineering.
Benini, E. and Giacometti, S. 2007. Design, manufacturing and operation of a small
turbojet-engine for research purposes. Applied Energy, 84 pp. 1102-1116.
Boresi, A. and Schmidt, R. 2003. Advanced Mechanics Of Materials. 6th ed. John
Wiley & Sons, Inc..
Callinan, J. and Hikiss, G. 2002. Operating Experience with the Turbine Technologies
SR-30 Turbojet Engine Test System. Proceedings of the American Society for
Engineering Education Annual Conference & Exposition.
Campbell, F. 2008. Elements of metallurgy and engineering alloys. Materials Park,
Ohio: ASM International, pp. 243-264.
Hafizah, N., Wahida, T., Azmin, F. and Ammar, A. 2012. Load Cell Application in
Rocket Thrust Measurement System. Applied Mechanics and Materials, 225 pp.
437-441.
Help.solidworks.com. n.d.. 2012 SolidWorks Help - Welcome to SolidWorks Simulation
Online Help. [online] Available at:
http://help.solidworks.com/2012/English/SolidWorks/cworks/IDC_HELP_HELPT
OPICS.htm?id=041a3037d280475ba40651617b4ab53c [Accessed: 29 July 2013].
Juste, G., Montanes, J. and Velasquez, A. n.d.. Micro-Jet Test Facility for Aerospace
Propulsion Engineering Education.
66
Lee, J., Yoon, J., Kim, T. and Sohn, J. 2007. Performance Test and Component
Characteristics Evaluation of a Micro Gas Turbine. Journal of Mechanical Science
and Technology, 21 (1), pp. 141-152.
Léonard, O., Thomas, J. and Borguet, S. 2009. Ten Years of Experience With a Small
Jet Engine as a Support for Education. Journal of Engineering for Gas Turbines
and Power, 131.
Leong, C., Jacob, J. and Liou, W. 2004. "Development of a Turbojet Engine Lab for
Propulsion Educaiton", paper presented at 40th AIAA/ASME/SAE/ASEE Joint
Propulsion Conference and Exhibit, Fort Lauderdale, Florida, 11-14 July.
American Institute of Aeronautics and Astronautics.
Mattingly, J. 2006. Elements of propulsion. Reston, Va.: American Institute of
Aeronautics and Astronautics.
May, D., Farber, S., Poirier, V., Chen, C. and Stiharu, I. n.d.. Design of a
Comprehensive Condition Monitoring System for Gas Turbine Engines.
Perez-Blanco, H. 2003. "Activities Around the SR-30 Minilab at PSU", paper presented
at 2003 American Society of Engineering Education Annual Conference and
Exposition, American Society of Engineering Education.
Pourmovahed, A., Jeruzal, C. and Brinker, K. 2003. "Development of a Jet Engine
Experiment for the Energy Systems Laboratory", paper presented at 2003 ASME
International Mechanical Engineering Congress, Washington, D.C., USA, 15-21
November. American Society of Mechanical Engineers.
Ross, C. 1998. Advanced finite element methods. Chichester: Horwood Pub..
Royce Plc, R. 1986. The Jet Engine. 4th ed. Derby: Rolls Royce plc.
Roylance, D. 2011. Finite Element Analysis. [Notes]. Department of Materials Science
and Engineering, Massachusetts Institute of Technology, Cambridge,
Massachusetts.
Santos, E., Alves, W., Almeida Prado, A. and Martins, C. 2011. Development of test
stand for experimental investigation of chemical and physical phenomena in Liquid
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Rocket Engine. Journal of Aerospace Technology and Management, 3 (2), pp. 159-
170.
Spang III, H. and Brown, H. 1999. Control of jet engines. Control Engineering
Practice, 7 pp. 1043-1059.
Tanabe, M., Kuwahara, T. and Aoki, K. 2003. "Development of a Small Jet Engine Test
System for University Education", paper presented at International Gas Turbines
Congress, Tokyo, 2-7 November. Gas Turbine Society of Japan.
Turbine Technologies Ltd. 2007. SR-30 Specifications. [report] Chetek, WI USA:
Turbine Technologies Ltd..
Vuong, A. 2012. Adaptive hierarchical isogeometric finite element methods.
Wiesbaden: Springer Spektrum.
Walsh, P. and Fletcher, P. 2004. Gas turbine performance. 2nd ed. Oxford: Blackwell
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GauravGururajShenoy_Dissert_Final

  • 1. Improvements to the design of the Jet engines experiment A dissertation submitted to the University of Manchester for the degree of Master of Science in Thermal Power & Fluids Engineering in the Faculty of Engineering and Physical Sciences 2013 Gaurav Gururaj Shenoy School of Mechanical, Aerospace and Civil Engineering
  • 2. 2 Table of Contents List of Figures ...................................................................................................................5 List of Tables.....................................................................................................................7 Nomenclature....................................................................................................................8 List of Abbreviations.........................................................................................................8 Abstract .............................................................................................................................9 Declaration......................................................................................................................10 Copyright ........................................................................................................................11 Acknowledgement...........................................................................................................12 Chapter 1 INTRODUCTION..........................................................................................13 1.1. Background........................................................................................................13 1.2. Role of Micro-Jet engines in Education ............................................................13 1.3. Objectives ..........................................................................................................15 Chapter 2 LITERATURE SURVEY .............................................................................17 2.1. Background........................................................................................................17 2.2. Findings .............................................................................................................17 2.2.1. Design of a Turbojet Engine Lab for Propulsion Education (Leong et al, 2004) ....................................................................................................................17 2.2.2. Ten years of experience with a small jet engine as a support for education (Léonard et al, 2009)...............................................................................................19 2.2.3. Developing a jet engines experiment for the energy systems laboratory (Pourmovahed et al, 2003)......................................................................................22
  • 3. 3 2.2.4. Micro-Jet test facility for Aerospace Propulsion Engineering Education (Juste et al, n.d.) ......................................................................................................24 2.2.5. Development of test stand for experimental investigation of chemical and physical phenomena in Liquid Rocket Engine (Santos et al, 2011) .......................26 2.2.6. Data Analysis and Performance Calibration of a small turbojet engine (Bakalis and Stamatis, 2011)...................................................................................28 2.2.7. Design of a small jet engine test system for university education (Tanabe et al, 2003)...................................................................................................................31 2.2.8. Operating experience with the Turbine Technologies SR-30 turbojet engine test system (Callinan and Hikiss, 2002)..................................................................32 2.2.9. Characterising the performance of an SR-30 turbojet engine (Witkowski et al, 2003)...................................................................................................................35 2.3. Summary............................................................................................................37 2.4. Conclusion.........................................................................................................39 Chapter 3 DESIGN METHODOLOGY & MODELING...............................................40 3.1. Background........................................................................................................40 3.1.1. Finite Element Analysis..............................................................................40 3.1.2. Design Criterion – Distortion Energy Density Criterion ............................41 3.1.3. About the software......................................................................................41 3.2. Selection of Material for the structure...............................................................42 3.3. Modeling............................................................................................................43 3.3.1. Design 1 ......................................................................................................45 3.3.2. Design 2 ......................................................................................................46 3.3.3. Design 3 ......................................................................................................47 3.3.4. Design 4 ......................................................................................................48
  • 4. 4 3.4. Input parameters for Simulation........................................................................48 3.4.1. Definition of Material .................................................................................48 3.4.2. Fixture & Loading details...........................................................................49 3.5. Summary............................................................................................................50 Chapter 4 RESULTS AND DISCUSSION.....................................................................51 4.1. Thrust Measurement..........................................................................................51 4.2. Simulation results ..............................................................................................52 4.3. Other Parameters ...............................................................................................56 Chapter 5 INSTRUMENTATION IMPROVEMENTS .................................................58 Chapter 6 CONCLUSION AND SCOPE FOR FUTURE WORK.................................62 6.1. Conclusion.........................................................................................................62 6.2. Scope for future work........................................................................................63 References:......................................................................................................................64
  • 5. 5 List of Figures Figure 2-1 Arrangement of the MW-54 showing instrumentation (Source: Leong et al, 2004) .......................................................................................................................18 Figure 2-2 Aluminum plate suspended using steel wires (Source: Léonard et al, 2009)20 Figure 2-3 (a) Load cell mounted to the test floor (b) Completed arrangement of the SR- 30 (Source: Léonard et al, 2009).............................................................................21 Figure 2-4 Arrangement of calibrated nozzle as an air flow meter measurement device (Source: Léonard et al, 2009)..................................................................................21 Figure 2-5 Mounting arrangement of the SR-30 at Kettering University (Source: Pourmovahed et al, 2003) .......................................................................................24 Figure 2-6 (a) Mounting arrangement of the Olympus HP (b) Schematic representation of pressure and temperature probes at various stations (Source: Juste et al, n.d.)..26 Figure 2-7 (a) Schematic arrangement of the L5 (b) AutoCAD drawing of the arrangement (Source: Santos et al, 2011) ...............................................................27 Figure 2-8 Schematic arrangement of sensors around the Olympus HP (Source: Bakalis & Stamatis, 2011) ...................................................................................................29 Figure 2-9 (a) Pressure and temperature v/s engine speed at compressor exit (b) pressure and temperature v/s engine speed at turbine exit (c) TIT and thrust v/s engine speed (Source: Bakalis & Stamatis, 2011)........................................................................30 Figure 2-10 Mounting arrangement of the custom small-scale jet engine at Nihon University, Japan (Source: Tanabe et al, 2003) ......................................................31 Figure 2-11 Standard mounting arrangement of the SR-30 at Loyola Marymount University (Source: Callinan & Hikiss, 2002) ........................................................34 Figure 2-12 Thrust v/s engine speed obtained during experiments (Source: Callinan & Hikiss, 2002) ...........................................................................................................34
  • 6. 6 Figure 3-1 (a) Exploded view of design 1 (b) Schematic arrangement of design 1........45 Figure 3-2 (a) Exploded view of design 2 (b) Schematic arrangement of design 2........46 Figure 3-3 (a) Exploded view of design 3 (b) Schematic arrangement of design 3........47 Figure 3-4 (a) Exploded view of design 4 (b) Schematic arrangement of design 4........48 Figure 3-5 Fixture and loading details on (a) Design 1 (b) Design 2 (c) Design 3 (d) Design 4 ..................................................................................................................49 Figure 4-1 Von-Mises stresses in (a) Design 1 (b) Design 2 (c) Design 3 (d) Design 4 – AISI 1020 Steel material.........................................................................................52 Figure 4-2 Displacements in (a) Design 1 (b) Design 2 (c) Design 3 (d) Design 4 – AISI 1020 Steel Material .................................................................................................53 Figure 4-3 Strains in (a) Design 1 (b) Design 2 (c) Design 3 (d) Design 4 – AISI 1020 Steel material...........................................................................................................53 Figure 4-4 Von-Mises stress in (a) Design 1 (b) Design 2 (c) Design 3 (d) Design 4 – Aluminum 1060 Alloy ............................................................................................54 Figure 4-5 Displacements in (a) Design 1 (b) Design 2 (c) Design 3 (d) Design 4 – Aluminum 1060 Alloy ............................................................................................55 Figure 4-6 Strains in (a) Design 1 (b) Design 2 (c) Design 3 (d) Design 4 – Aluminum 1060 Alloy...............................................................................................................55
  • 7. 7 List of Tables Table 1 - Details on different sensors at stations (Source: Bakalis & Stamatis, 2011)...29 Table 2 - Results obtained for the SR-30 at LMU (Source: Callinan & Hikiss, 2002) ..35 Table 3 - Temperature at the compressor exit calculated using three different methods (Source: Witkowski et al, 2003)..............................................................................36 Table 4 - Results obtained on the SR-30 at the University of Minnesota (Source: Witkowski et al, 2003)............................................................................................37 Table 5 - Summary of literature review..........................................................................38 Table 6 - Material properties (Source: SolidWorks 2012 material library)....................42 Table 7 Summary of results ............................................................................................56 Final Word Count – 11,912
  • 8. 8 Nomenclature Uo – Total strain energy Uv – Strain energy causing volumetric change UD – Strain energy causing distortion σ1, σ2, σ3 - Principle stresses K – Bulk modulus G - Rigidity modulus List of Abbreviations ABET – Accreditation Board of Engineering and Technology CAD – Computer Aided Design ECU – Engine Control Unit EGT – Exhaust Gas Temperature IAE – Institute of Aeronautics and Space LOX – Liquid Oxygen LPL – Liquid Propulsion Laboratory MGT – Micro Gas Turbine NPSA – National Plan of Space Activities RPM – Revolutions Per Minute TIT – Turbine Inlet Temperature UAV – Unmanned Aerial Vehicle
  • 9. 9 Abstract Education about propulsion systems has been an important area of study over a number of years. In order to provide a practical approach for students, many Universities have adopted the technique of using small-scale jet engines to demonstrate the thermodynamics propulsion systems. This has become easier with the recent development of such jet engines for radio controlled aircraft. Small-scale jet engines are essentially the same jet engines that we see in an aircraft, but smaller in capacity, size, power and some other operating parameters. Factors like temperature, pressure etc. can be similar to those on full size jets. In order to study the performance of a jet engine, the parameters have to be monitored continuously and the performance analysis can be carried out in different ways (analytical, theoretical or computational). The first part of the study aims at looking at the literature for the methods adopted in mounting such small-scale engines and instrumentation implemented. The second part looks at different designs developed to mount the small-scale engine, a finite-element study in these designs and studying the maintenance, safety factors involved in these designs. Choosing the optimum design and any suggestions to the improvements in instrumentation follows an overall study of the design. A modified version of the mounting structure adopted by Léonard et al (2009) was chosen to be the optimum design.
  • 10. 10 Declaration No portion of the work referred to in the dissertation has been submitted in support of an application for another degree or qualification of this or any other university or other institute of learning.
  • 11. 11 Copyright i. The author of this dissertation (including any appendices and/or schedules to this dissertation) owns certain copyright or related rights in it (the “Copyright”) and s/he has given The University of Manchester certain rights to use such Copyright, including for administrative purposes. ii. Copies of this dissertation, either in full or in extracts and whether in hard or electronic copy, may be made only in accordance with the Copyright, Designs and Patents Act 1988 (as amended) and regulations issued under it or, where appropriate, in accordance with licensing agreements which the University has entered into. This page must form part of any such copies made. iii. The ownership of certain copyright, patents, designs, trade marks and other intellectual property (the “Intellectual Property”) and any reproductions of copyright works in the dissertation, for example graphs may not be owned by the author and may be owned by third parties. Such Intellectual Property and Reproductions cannot and must not be made available for use without the prior written permission of the owner(s) of the relevant Intellectual Property and/or Reproductions. iv. Further information on the conditions under which disclosure, publication and commercialization of this dissertation, the Copyright and any Intellectual Property and/or Reproductions described in it may take place is available in the University IP Policy (see http://documents.manchester.ac.uk/display.aspx?DocID=487), in any relevant Dissertation restriction declarations deposited in the University Library, The University Library’s regulations and in The University’s Guidance for the Presentation of Dissertations. (See http://www.manchester.ac.uk/library/aboutus/regulations)
  • 12. 12 Acknowledgement I would like to express my sincerest gratitude to my dissertation guide Dr. Andrew Kennaugh for presenting me with this exciting topic for my dissertation, guiding me throughout the process of research undertaken. His valuable advises have been helpful in successful completion of this dissertation. I would like to take this opportunity to thank my father for giving me all the support and my mother for her unconditional love and confidence in me, which has helped me in pursuing my education so far. I would like to thank Late Prof. K Sridharan, Retired Professor in Civil Engineering, Indian Institute of Science, Bangalore, who was my inspiration to pursue this field of engineering and motivated me to continue further. Finally, I would like to thank all my friends and family for supporting me throughout my career and helping me go through ups and downs of life.
  • 13. 13 Chapter 1 INTRODUCTION 1.1. Background Aerospace engineering has seen major improvements in many areas with the advancements in technology. These improvements are also seen amongst the number of students opting to pursue education in this field of engineering. Under the Bologna Initiative in Europe, steps are being taken to produce well-trained professionals and recruit them into leading companies that compete on a global scale (Juste et al. n.d.). Juste et al. (n.d.) suggested many different ways to improve the quality of Aerospace education. A more concurrent engineering approach was suggested during the course. Jet propulsion is one of the very important topics in the field of Aerospace engineering, which originated in the beginning of the 20th century (Juste et al., n.d.; Mattingly, 2006). However, there has been a rapid development in gas turbine engine technology since the 1950s (Royce Plc, 1986). In 1930, Frank Whittle developed the first gas turbine engine, which produced a propulsive jet and further went on to form a basis to the modern jet engines (Royce Plc, 1986). 1.2. Role of Micro-Jet engines in Education Higher education in this aspect of engineering often requires the understanding of jet propulsion by experimental or practical means (Perez-Blanco, 2003). In the course of understanding the science and technology, the process of experimentation and implementation is crucial (Perez-Blanco, 2003). The study of jet propulsion involves the design and implementation of prime movers for a large number of different applications. However, studying jet propulsion or jet engines involves an all-inclusive understanding of their working in the theoretical, computational and design aspects
  • 14. 14 (Juste et al, n.d.). Often, students find it difficult to understand the theory behind jet propulsion, as the jet engine is not something they come across in their day-to-day activities (Tanabe et al, 2003). In order to study the principle of jet propulsion in a practical sense, a small-scale jet engine or a Micro Gas Turbine (MGT) would be a good tool, bearing in mind the cost. Micro Gas Turbines are gas turbines, which are smaller in size and develop a power of up to 200kW. The pressure conditions in such engines are much smaller than those in bigger jet engines. However, the temperature conditions in small jet engines are similar to their bigger counterparts. The pressure ratio in these engines is low (Lee et al, 2007), typically around 4 compared to 15 in larger engines. This is because of the fact that small-scale engines are mostly single spool engines. These kinds of engines are used in universities for demonstration/experimental purposes and also to power unmanned aerial vehicles (UAV), remote-controlled aircrafts etc. (Benini & Giacometti, 2007). The use of a laboratory turbojet engine is desirable because of its ease to enable understanding the thermodynamic principles involved. Apart from this major advantage, the small turbojet engine is present-day device, which has great potential for improvement (Callinan & Hikiss, 2002). The ABET syllabus encouraged the use of laboratory turbojet engines with the aim of imparting knowledge on the working of the engine components and the whole system itself (Callinan & Hikiss, 2002; Leong et al, 2004). Bearing in mind the theoretical knowledge gained in classroom teaching, the laboratory turbojet engine is a useful tool to gain hands-on experience while working on it (Leong et al, 2004). Comparative studies also helps in understanding the behavior of different types of jet propulsion systems (turbojets, turbofans, turboprops) of different scales, as carried out by students at the West Michigan University (Leong et al, 2004).
  • 15. 15 One such jet engine in the engine-testing laboratory of the School of Mechanical, Aerospace and Civil Engineering (MACE) at the University of Manchester suffered a structural failure causing the exhaust duct to deform and jam against the turbine. This meant that a new engine was required with the choice being a direct replacement or the purchase of a different jet. It was decided to obtain a new type of jet engine and this meant the test stand required a new design for the engine to be mounted upon and also facilitating the instrumentation to record some additional pressures and temperatures etc. The objectives of the experiment include understanding the basic working principle of a jet engine; relating them to the various thermodynamic equations that are encountered in the theory, gain a brief insight on the use of instrumentation in the apparatus. 1.3. Objectives The School of MACE at the University of Manchester recently procured an Olympus HP electric-start jet engine manufactured and sold by AMT, Netherlands. This jet engine is capable of producing a maximum thrust of 230N at a maximum engine speed of 108,500 revolutions per minute (rpm) (AMT Netherlands, 2009). The engine is specifically modified by the manufacturer for University use and has additional connections for pressure and temperature measurements beyond those used for routine radio controlled operation. The objectives of the study cover the various designs of test stands that have been adapted in mounting such small size jet engines, looking up to the design factors like maintenance, reliability, safety and convenience of such designs and also the instrumentation involved in recording different parameters during the working of the engine. Furthermore, new designs will be developed and studied in the later part of the thesis.
  • 16. 16 As the test stand is a very important piece of equipment in the process of studying the engine, more importance was given in the design of the same. The primary requirement of the design was to make sure the test stand could take the maximum thrust produced by the engine with minimal distortion or deflection. Adding to this, it was kept in mind that the test stand required minimum maintenance and ensured safety of the personnel and surrounding in the unlikely event of any mechanical failure. This report consists of a literature survey that gives an insight of the different methods adopted to mount a small scale jet engine, different instrumentation adopted in the experimental setup and a brief outline of the results obtained. The literature review is followed by a methodology and modeling chapter, which lays out a briefing on the methods adopted in working towards the objective, and also the different arrangements modeled using a CAD package. Results are presented and discussed in the following chapter followed by the conclusion and recommendations for future work, if any.
  • 17. 17 Chapter 2 LITERATURE SURVEY 2.1. Background The aim of this literature survey is to understand the different types of test stands that have been incorporated in mounting small sized jet engines, various measuring techniques adapted in recording the different operating parameters during the working of the engine. Adding to this, the literature briefly covers the results that have been obtained while testing different small size engines. A detailed contribution of different authors has been presented in the succeeding section. 2.2. Findings 2.2.1. Design of a Turbojet Engine Lab for Propulsion Education (Leong et al, 2004) As a supplement to the theoretical knowledge gained in the classroom, two graduate students and a professor from the School of Mechanical and Aeronautical Engineering, West Michigan University, USA, developed a jet engine test cell facility. The engine used was a simplified, scaled down version of a turbojet engine - MW-54, developed by Wren Turbines Ltd. This jet engine works on the Brayton cycle and comprises of a single stage radial compressor and axial turbine. During the course of designing the test cell, there were plenty of sensors and other instrumentation devices that were integrated to measure various parameters during the operation of the engine. The engine was mounted on a spring-loaded slider platform. To measure the thrust developed by the engine, a modified servomechanism was installed along with a potentiometer to measure the resistance. The modified servo was linked to the platform by the means of a connecting rod. This connecting rod was used to convert the linear
  • 18. 18 motion of the slider to the angular motion of the servo arm. The servo arm was connected to the potentiometer. When the engine was in operation, the platform experienced a linear movement due to the thrust developed by the engine. Due to the linear movement, the servo arm rotates and a change in resistance is recorded by the potentiometer. A correlation between the chance in resistance and the engine thrust was deduced and thus the engine thrust was obtained. A pictorial representation of the engine is shown in figure 2-1. Figure 2-1 Arrangement of the MW-54 showing instrumentation (Source: Leong et al, 2004) Parameters like pressure, temperature and volume flow rates of air and fuel were recorded using various instruments. A pressure gauge was installed to measure the case pressure. In order to minimize resistance to the movement of the engine and minimize any forces that would affect the thrust measurement, nylon tubes were used to connect the pressure gauge and the pressure port on the engine. Exhaust gas temperature (EGT) measurements were done using simple thermocouples placed in the exhaust cone, close to the exhaust nozzle. According to the specifications of the engine given by the engine
  • 19. 19 manufacturer, the thermocouple was placed in such a way that only 2mm of the point of measurement was protruding into the exhaust stream. The engine speed was measured using a Hall effect sensor. A magnetic nut was installed on the compressor. As the shaft rotated, the magnet developed a magnetic flux, which was detected by the Hall effect sensor. This signal picked up by the sensor was then communicated to the engine control unit (ECU) and also to the display device on the test stand. Fuel flow rate was measured using an Infrared sensor and an impeller type flow meter. A fuel pump is always incorporated on an engine to make sure there is continuous flow of fuel passing into the engine. To monitor the flow rate of fuel, the flow meter was mounted downstream of the fuel pump, before the fuel passed into the engine. The flow meter was a turbine type meter so the fuel flow was measured as a linear function of the rotational speed of the turbine in the flow meter, the rotational speed being detected by an infra-red receiver that detected the passing turbine blades.. 2.2.2. Ten years of experience with a small jet engine as a support for education (Léonard et al, 2009) According to Léonard et al (2009), jet propulsion is one of the key concepts in a Masters level study in aerospace engineering. To provide an illustration for the students of the concept of jet propulsion, the School of Mechanical and Aerospace engineering at the University Of Liège, Belgium, procured a small jet engine. The motive to train students on data measurement, acquisition and interpretation was kept in mind. The engine procured had to meet the criteria of being able to be used in a laboratory environment and not so small that there would be compromises on provision of different sensors to measure the working parameters of the engine. The SR-30 mini turbojet engine by Turbine Technologies Ltd was chosen. The SR-30 is a single spool mini jet engine with a single stage radial compressor and an axial-flow turbine.
  • 20. 20 The test bench on which the engine was mounted underwent several modifications since 1997. The engine was taken away from the mounting legs of the old configuration and was mounted on an Aluminum plate. This plate was suspended from the frame using steel cables (figure 2-2). This was done to ensure the engine support place could move freely in response to the thrust developed as cables provide better frictionless movement than any other mechanism. In addition, flexible tubing was used to provide minimum resistance to the movement of the engine. A Z-type load cell was employed to measure the thrust developed. The load cell was mounted on the test floor, which would be engaged when the suspended aluminum plate pressed against it (figure 2-3(a)). Before the load cell could be used, a cable-pulley mechanism was used to calibrate the load cell. A schematic arrangement of the test setup is shown in the figure 2-3(b). Figure 2-2 Aluminum plate suspended using steel wires (Source: Léonard et al, 2009)
  • 21. 21 Figure 2-3 (a) Load cell mounted to the test floor (b) Completed arrangement of the SR- 30 (Source: Léonard et al, 2009) As a requirement to perform the complete analysis of the engine, the measurement of volume flow rate of air was essential. A calibrated nozzle replaced the bell-mouth of the stock engine. This arrangement is shown in figure 2-4. The difference in the pressure at the throat of the engine and the atmospheric pressure was calculated and hence the volumetric flow rate of air was deduced. The technique used to measure the flow rate of fuel was similar to that used in a diesel engine. A cavity of known volume fills up and empties each time the fuel is supplied and this process repeats. A sensor was deployed to sense this filling and emptying cavity. The sensor sends the signal to an electric device and the frequency of the signal is converted to the fuel flow rate. Figure 2-4 Arrangement of calibrated nozzle as an air flow meter measurement device (Source: Léonard et al, 2009)
  • 22. 22 As a provision to control the engine using the airflow rate, a variable area nozzle was installed. The default feature of the engine was the ability to control the power developed by the engine using the fuel flow rate. The addition of this calibrated nozzle meant that it was additional control parameter. This addition was done with an intention to study the compressor characteristics. On concluding the study, it was observed that the single-point method of measurement (one-dimensional) was not an accurate way of obtaining the parameters. With the many modifications done over a period of time, the apparatus was successful as an educational tool because it provided a deep understanding of various scientific phenomena. 2.2.3. Developing a jet engines experiment for the energy systems laboratory (Pourmovahed et al, 2003) With the same motive as seen in the previous papers (Léonard et al, 2009; Leong et al, 2004), a scaled down jet engine was installed in the energy systems laboratory of Kettering University, USA. The engine installed was the SR-30 turbojet engine. Many other authors (Léonard et al, 2009) have studied this engine and have published their experiences. At the time of initial testing of the engine, it was found that the methods used to measure thrust developed, fuel flow rate and engine speed were inadequate, inaccurate and less reliable. Hence, the test rig was subjected to a dramatic makeover. The structure on which the engine was mounted was easily distorted and affected the thrust measurements significantly. The thrust measurement was further not reliable as the load transducer used was outdated and inaccurate. There was no technique used to monitor the airflow rate into the engine. The constraint on the engine support was beyond the point of acceptance, which hampered the linear displacement of the engine due to thrust, thus giving out poor thrust reading. The structure was such that the front
  • 23. 23 leg was supported firmly onto the test floor and the rear leg was not fixed. This resulted in the engine not thrusting against the load transducer, thus giving out inaccurate thrust reading. Moreover, because the rear leg was not bolted to the floor, the engine rotated around the mounting bolts of the front leg, thus restraining it against engaging the load cell. The load transducer used had a number of downfalls: it was a simple, strain-gauge type of a load transducer which had no temperature compensation which means it was never able to compensate for the change in system temperature while working in a high temperature environment. The sensitivity was low, inaccurate and the load transducer was mounted well below the centerline of the engine. All these factors put together, it lead to a large margin of error which was unacceptable and needed amendment. The engine supports were modified such that the engine was suspended using four straps of steel shim stock. This ensured less resistance that meant the engine experienced free movement and avoid any unlikely event of the engine twisting or moving laterally. Complementing to the responsiveness, flexible tubing were used on the pressure gauges connecting the pressure ports. An upmarket load transducer was used which had high sensitivity and accuracy (up to 0.1lbF). Linear variation and compensation to temperature were added advantages to the load transducer. The structure operated so that it restrained the engine to move only axially against the load cell, ensuring accurate readings of thrust. The method adopted by Léonard et al (2009) was used to calibrate the load cell. A pictorial representation of the modified arrangement is shown in figure 2-5.
  • 24. 24 Figure 2-5 Mounting arrangement of the SR-30 at Kettering University (Source: Pourmovahed et al, 2003) Relevant equipment to measure the flow rate of fuel and air were used. The flow rate of fuel was recorded using a gravimetric approach. This method detected the change in weight of fuel to calculate the flow rate. The old setup measured the engine speed by converting the frequency to direct voltage. A direct frequency counter that returned the voltage in both analog and digital forms replaced this. With the aim of studying the emissions from the engine, a gas analyzer (Horiba MEXA 7100D) was used. 2.2.4. Micro-Jet test facility for Aerospace Propulsion Engineering Education (Juste et al, n.d.) The School of Aeronautics, Aerospace propulsion and Fluid Mechanics at the Universidad Politecnica de Madrid installed a micro-jet engine as an educational tool to enable students to understand the physical phenomena in the operation of a jet engine. The heart of the apparatus was the Olympus HP micro-jet engine developed and manufactured by AMT Netherlands. The Olympus HP, like any other mini-jet engines used by Leong et al (2004) and Léonard et al (2009), has a single stage centrifugal compressor, axial flow turbine, bell mouth inlet and a convergent exhaust nozzle.
  • 25. 25 The Engine Control Unit (ECU) is a key component present in the Olympus HP that is useful in monitoring the working conditions. It assists in starting and stopping of the engine makes the engine fail-safe and also includes basic telemetry software which monitors several parameters like the exhaust gas temperature (EGT), engine speed. A detailed technical specification of the Olympus HP can be found in the datasheet (AMT Netherlands, 2009). With an intention to study the performance of the engine, different parameters like flow rates of air and fuel, thrust, pressure and temperatures at different stations of the engine have to be measured. The ambient conditions of temperature and pressure are also recorded. The engine was mounted on the test stand, which was bolted to the test floor. A load cell was placed on a pedestal, which was bolted to the floor. The engine, when in operation, was restrained axially by the load cell, which gave out the thrust reading. Thermocouples and pressure probes were installed at each station to measure the respective parameters. Pneumatic signals from the pressure probe were sent to their respective pressure transducers to obtain the pressure reading at that station. It was proposed to install sensors all over the circumference at each station, as the flow around the circumference would be non-uniform. However, this circumferential arrangement of sensors was not implemented, as multiple sensors would block the flow of the gases (because the clearance between the combustion chamber and outer casing was found to be 5.2mm). This interference of the gases would essentially drop the performance of the engine, which was a demerit. As it is understood that the temperature at the combustor exit is very high, two thermocouples placed laterally opposite to each other were used to record the temperature at this station. A pictorial representation of the test setup and the details of pressure, temperature sensors at each station is represented in figure 2-6(a) and figure 2-6(b) respectively.
  • 26. 26 Figure 2-6 (a) Mounting arrangement of the Olympus HP (b) Schematic representation of pressure and temperature probes at various stations (Source: Juste et al, n.d.) The measurement of fuel flow rate was done using a turbine flow meter. Measuring the engine speed was done by a magnetic pickup installed in the compressor, which created a magnetic flux against a sensor during operation. These arrangements for measuring flow rate of fuel and engine speed were used by Leong et al (2004). A calibrated nozzle technique was proposed to measure the flow rate of air. However, this technique was discarded citing a problem of the engine size. Alternatively, an indirect method of calculating the airflow was executed by taking the temperature and pressure readings at the exit of the exhaust nozzle following a calibration task. 2.2.5. Development of test stand for experimental investigation of chemical and physical phenomena in Liquid Rocket Engine (Santos et al, 2011) Through the National Plan of Space Activities (NPSA), the Brazilian Space Agency has invested in a group of experts to carry out calculation, design and construction of Liquid Rocket Engines (LREs). As a part of the agency’s space venture, the Institute of Aeronautics and Space (IAE) tested the L5 jet engine. The L5 engine is a large-scale jet engine running on Liquid Oxygen (LOX) and kerosene, used in the Brazilian Vehicle Launcher for Satellites that develops a maximum thrust of 5000N. The thrust developed
  • 27. 27 by this engine was tested at the Liquid Propulsions Laboratory (LPL) located in São José dos Compos. The thrust testing apparatus consists of an interface support that allows fixing of the engine onto it. The engine was fixed vertically so that the thrust force exerted is upwards (exhaust is facing the surface of the earth). A cable-pulley mechanism was used to calibrate the load cell used in the apparatus. A voltage proportional to the thrust force was obtained when the engine restrained against the strain gauge, load cell. A schematic arrangement and an AutoCAD drawing of the arrangement is shown in figure 2-7. Figure 2-7 (a) Schematic arrangement of the L5 (b) AutoCAD drawing of the arrangement (Source: Santos et al, 2011) Although this setup was used on a large-scale engine, a similar test arrangement can be developed based on the same grounds. However, the apparatus does not restrain the twisting or movement of the engine in the lateral direction. Moreover, toppling of the engine with respect to the horizontal plane is also possible.
  • 28. 28 2.2.6. Data Analysis and Performance Calibration of a small turbojet engine (Bakalis and Stamatis, 2011) Bakalis and Stamatis (2011) from the department of Mechanical engineering at the University of Thessaly, Volos, Greece, developed a simulation model of a small turbojet engine. The small turbojet engine used was the same as the one used by Juste et al (n.d.) in Madrid. A detailed technical specification of the engine can be found in the datasheet (AMT Netherlands, 2009). A number of discrepancies were observed mainly in the temperature and pressure recording exercise. These measurement errors were mainly because of the irregular flow-fields in the jet. During the study of the engine, it was found that a temperature gradient was spread across, all around the engine, which hampered the temperature measurements at different stations. Because there was heat transfer within the stations, a difference between the actual temperature and measured temperature was observed. At the turbine exit, a drop in pressure was observed in the axial and radial directions, which made it difficult for the pressure sensors to measure the pressure accurately. Taking into account these inconsistencies, it has to be noted that the high temperature and pressure variations have to be taken into account while evaluating the performance of the engine, to avoid abnormal results. Control of the Olympus HP turbojet engine is mainly executed by an ECU. Juste et al (n.d.) explained the role of the ECU in the Olympus HP engine. The version of the Olympus HP used in this study had extra measuring points for pressure and temperature at each station so as to obtain accurate, all round measurements. A schematic arrangement of the engine showing different stations and location of the sensors is shown in figure 2-8.
  • 29. 29 Figure 2-8 Schematic arrangement of sensors around the Olympus HP (Source: Bakalis & Stamatis, 2011) All the measuring probes are installed at the mean radius, except for the static pressure probes. The different sensors incorporated at each station are given in table 1. Table 1 - Details on different sensors at stations (Source: Bakalis & Stamatis, 2011) The ECU monitors the engine speed and EGT and maintains it within acceptable limits. The EGT sensor is incorporated between the turbine exit and the nozzle entry (station 7) and is linked to the ECU in order to control the engine. This means that maintaining the
  • 30. 30 EGT can be one of the ways of controlling the engine. A Z-type load cell of capacity 590N was used to measure the thrust. Bakalis & Stamatis (2011) stated that in order to minimize or eliminate the errors, data collection had to be done accurately, using a reliable method. Under steady-state conditions, the engine was tested from idle speed to the maximum speed and various results were presented. Pressures and temperatures at the compressor and turbine exit were plotted with varying engine speed. Similarly, the turbine inlet temperature (TIT) and the thrust exerted were plotted with engine speed and all these plots are shown in figure 2-9. Figure 2-9 (a) Pressure and temperature v/s engine speed at compressor exit (b) pressure and temperature v/s engine speed at turbine exit (c) TIT and thrust v/s engine speed (Source: Bakalis & Stamatis, 2011)
  • 31. 31 2.2.7. Design of a small jet engine test system for university education (Tanabe et al, 2003) Undergraduate students from the department of aerospace engineering at the Nihon University, Japan, contributed in developing a small jet engine testing facility. The apparatus was designed to impart an effective understanding of the working of a jet engine. Unlike any other university, the students designed the engine in-house. This allowed a better understanding on not only the operation of the engine, but the design and manufacture of the engine components as well. The duration of the whole project was well above one year. As a modification exercise, it was decided that an automotive turbocharger would be used on the engine to provide the compression stage and the students would be given the task to design the combustor and the nozzle. The project was looked into by two sets of students: the first set looking at understanding the automotive turbocharger, designing the components whereas the second set looked at overall improvement of the design of the test facility. A schematic arrangement of the test facility is shown in the figure 2-10. Figure 2-10 Mounting arrangement of the custom small-scale jet engine at Nihon University, Japan (Source: Tanabe et al, 2003)
  • 32. 32 As depicted, the engine is made to hang from the ceiling using four fine steel wires. The principle of this arrangement is something similar to that, seen in Léonard et al (2009). Because the engine is freely suspended, the movement of the engine during operation is restrained minimally. Routing components like hoses and wires are also hung to avoid resisting the engine movement. A load cell was fixed to a plate, which was suspended from the ceiling. The engine, when in operation, would exert the thrust onto this load cell, thus giving the thrust value. Airflow measurement was done using a flow meter, which was installed in between the air filter and the turbocharger. The temperatures and pressures at vital components like compressor, combustor and turbine were monitored and controlled within their respective capacities. K-type and J-type thermocouples were used to measure the temperature at various stations of the engine. Semi-conductor type pressure sensors (COPAL PG-30-102R/103R) were used to record the pressures. The engine speed was measured using a magnetic detector, which created a magnetic flux during operation, and a sensor recorded the pulse to give out the engine speed-reading. A piezoelectric sensor was used to measure the amount of vibrations in the system. 2.2.8. Operating experience with the Turbine Technologies SR-30 turbojet engine test system (Callinan and Hikiss, 2002) In 1999, the mechanical engineering department of the Loyola Marymount University (LMU), USA, decided to acquire a scaled down turbojet engine to be used as an experimental device for the undergraduate students in mechanical and aerospace engineering. The engine was installed at the Thermal Sciences laboratory of the LMU. The heart of the experimental setup was the SR-30 mini turbojet engine developed by Turbine Technologies ltd. The SR-30 follows the usual design arrangement as many other mini jet engines (Olympus HP, MW-54) i.e. a single stage centrifugal compressor and axial turbine arrangement. A detailed specification has been given in the datasheet
  • 33. 33 (Turbine Technologies ltd, 2007). The MinilabTM comprises of the SR-30 engine, supporting equipment used for operation and control of the engine, a safety enclosure within which the engine is housed, instrumentation to measure operational parameters and a data acquisition system to collect, process the data. As a part of the academic exercise, parameters like the specific thrust, component efficiencies (combustor, turbine, and compressor), air-fuel ratio, thrust specific fuel consumption and the specific thrust are calculated. To compare the thrust recorded mechanically, an alternative thrust reading is calculated using the exhaust nozzle data. The engine was installed as per the specifications provided by the manufacturer. The instrumentation comprises of devices to mention the temperature, pressures, thrust etc. K-type thermocouples are used to determine the temperature at different stations (compressor inlet, combustor inlet, turbine inlet and exhaust inlet & outlet). Piezoelectric transducers are employed to calculate the pressures at these different stations. A 2-pole generator is used to measure the engine speed. Thrust is measured using a strain gauge type load cell. The engine is mounted on two legs bolted to the test floor. The load cell is mounted at a height half way through the centerline of the engine. It is placed in such a way that the engine restrains against it during operation. A pictorial representation of the arrangement is shown in figure 2-11. Figure 2-12 shows the variation of thrust as a function of the engine speed. The data acquisition system links the different sensors and assists in collecting and processing of the data. Digital display devices are used to indicate different parameters like the oil pressure, compressor air pressure, EGT, engine speed etc. A throttle lever is also provided to vary the speed of the engine. A multi-meter is used to output the readings from the pressure transducers of different stations, fuel flow rate and the readings from the load cell.
  • 34. 34 Thermocouple output is executed using an Omega model DP25-TC digital thermocouple controller. Figure 2-11 Standard mounting arrangement of the SR-30 at Loyola Marymount University (Source: Callinan & Hikiss, 2002) Figure 2-12 Thrust v/s engine speed obtained during experiments (Source: Callinan & Hikiss, 2002) With all the instrumentation in place, the engine was operated at different speeds. The parameters obtained using the instrumentation were recorded and graphs were plotted as a function of engine speed. Typical results obtained in the test have been tabulated in table 2. In the table, nozzle efficiency reads 211%, which is an unrealistic figure. This inconsistency is due to the incorrect temperature reading at the turbine inlet.
  • 35. 35 Table 2 - Results obtained for the SR-30 at LMU (Source: Callinan & Hikiss, 2002) 2.2.9. Characterising the performance of an SR-30 turbojet engine (Witkowski et al, 2003) The SR-30 small-scale turbojet engine is being used as an important educational tool in many universities across the world. As discussed earlier, the SR-30 follows the conventional configuration of a small-scale turbojet engine i.e. a single stage centrifugal compressor and an axial turbine. For the students to record respective parameters and conduct a thermodynamic study, temperature and pressure sensors have been installed at each station of the engine. The limitation of the study is that the analysis carried out is one-dimensional and hence the results that were obtained would not look practical. At the inlet nozzle, the pressure was calculated using the pressure differential between the pressure of the flow entering the engine and the atmospheric pressure. As the SR-30 has a bell mouth shaped inlet nozzle, it serves in creating a uniform velocity profile. Using this uniform velocity profile as an assumption, the mass flow rate of air entering the engine could be calculated. Flexibility in the installed probes meant that the operator had the liberty to reposition the sensors. The reason behind that was to study the difference in the calculations performed by the students when the positions of the sensors were switched. During the starting of the engine, thermal transients were
  • 36. 36 observed within the engine. For these transients to reach a steady state, the engine had to be kept on idle before any analysis was done. In order to tackle this problem of thermal transients, three different types of starting (cold, medium, hot) was done on the SR-30 and the temperature at the compressor exit was recorded. The temperature at the compressor exit was measured using two temperature probes. The first probe was fixed, facing the exhaust nozzle plane and the second probe was allowed to traverse along a defined path to obtain a detailed profile measurement of the exhaust cone. The temperature at the compressor exit was found to vary around the circumference. To overcome this issue, the students were asked to integrate the temperature over the inner wall to the outer wall. An alternative method was to place thermocouples all around the circumference and take the average value. A total of three different methods were adopted to measure the temperature at the compressor exit. The three methods were integrated method, average method and the midpoint method. The results using the three methods have been presented in table 3. In measuring the temperature at the combustion chamber, a temperature difference of about 50-70 degrees Celsius was observed between the outer wall of the combustion chamber and the inner wall of the casing (distance of 10mm). The pressure reading however, hardly varied. The results obtained from the experiment are presented in table 4. Table 3 - Temperature at the compressor exit calculated using three different methods (Source: Witkowski et al, 2003)
  • 37. 37 Table 4 - Results obtained on the SR-30 at the University of Minnesota (Source: Witkowski et al, 2003) 2.3. Summary To give a brief insight of the literature, the findings from each paper have been tabulated as shown in table 5.
  • 38. 38 Year/Author University Engine Mounting Method Thrust Measurement Instrumentation Leong et al, 2004 Western Michigan University, USA MW-54, Wren Turbines Ltd. Spring- loaded slider platform Modified servomechanis m, potentiometer Hall effect sensor for engine speed, impeller type flow meter for fuel flow rate Léonard et al, 2009 University Of Liège, Belgium SR-30, Turbine Technolo gies Ltd. Mounted on Aluminium plate, suspended using steel cables Load cell mounted to the test floor Calibrated nozzle for air-flow measurement, emptying cavity type fuel flow measurement Pourmovahed et al, 2003 Kettering University, USA SR-30, Turbine Technolo gies Ltd. Suspended using four straps of steel shim stock Load cell mounted on the test floor Gas analyser, air flow measurement Juste et al, n.d. Universidad Politecnica de Madrid, Spain Olympus HP, AMT Netherlan ds Mounted on cantilever beam, bolted to test floor Load cell mounted on a pedestal ECU, Circumferential placement of sensors, turbine flow-meter for fuel, magnetic pickup sensor for speed Bakalis and Stamatis, 2011 University of Thessaly, Greece Olympus HP, AMT Netherlan ds Not mentioned Z-type load cell ECU, Circumferential placement of sensors Tanabe et al, 2003 Nihon University, Japan Self-built Suspended from the ceiling using four steel wires Load cell was suspended from the ceiling Turbine flow- meter for fuel, magnetic detector for engine speed, piezoelectric sensor for vibrations Callinan and Hikiss, 2002 Loyola Marymount University, USA SR-30, Turbine Technolo gies Ltd. Mounted on two legs bolted to test floor Load cell placed on a pedestal, close to the centreline of exhaust 2-pole generator for engine speed, display devices for instrumentation Witkowski et al, 2003 University of Minnesota, USA SR-30, Turbine Technolo gies Ltd. Not mentioned Load cell mounted on the test floor Pressure and temperature sensors Table 5 - Summary of literature review
  • 39. 39 2.4. Conclusion So far, the literature has given an account of the various mounting methods of small- scale jet engines, different instrumentation used and their role in studying the performance of the engine. Looking at the different mounting techniques, the movement of the engine has to be restrained minimally so that the accuracy of the thrust reading is enhanced. As there are no mechanical parts present in the suspended way of mounting, this would be an ideal way to achieve a linear motion with minimum resistance. These designs were adopted by Léonard et al (2009) & Tanabe et al (2003). The literature also describes the different techniques adapted to record parameters like temperature, pressure, and flow rates of air & fuel. Apart from these basic parameters, Pourmovahed et al. (2003) used a gas analyzer to study the emissions from the engine. On a concluding note, the literature review forms a foundation to the succeeding research in this topic of improvisations to the small-scale jet engine experiment at the University of Manchester. With the help of the literature, the demerits were identified and improvisations were recommended. Furthermore, new techniques of measuring necessary parameters are discussed.
  • 40. 40 Chapter 3 DESIGN METHODOLOGY & MODELING 3.1. Background The basis of this chapter is for the reader to understand the structure adopted, in carrying out the research. The existing model (shown in Turbine Technologies ltd, 2007) was studied briefly and the downfalls in the model were many. The mounting structure had to be completely redesigned and the instrumentation had to be replaced as well. As an ideal way of designing, multiple models were created and studied thoroughly using SolidWorks 2012. The study involved two basic steps – feasibility study and a simulation study. Feasibility study involved a basic study, which was done by visually analyzing the model, discussing the ease of maintenance, and safety factors in the design. Simulation study involved a rigorous study of the model using a Finite Element Analysis (FEA) method. The results gathered from the FEA were then compared and a conclusion was reached. Additional instrumentation, which could be helpful in executing a detailed analysis of the engine, was suggested. 3.1.1. Finite Element Analysis In the modern world, a rapid development has been observed in the field of numerical analysis and simulation. Numerical simulation has emerged as a key technology in the scientific and industrial applications (Roylance, 2011). One such numerical simulation method used to study physical structures is called Finite Element Method (FEM) or Finite Element Analysis (FEA). FEM involves numerically breaking the structure into a large number of small entities called finite elements. These elements take different shapes and sizes in order to match the physical geometry. This method is used to study complex shapes where conventional methods like matrix displacement methods cannot
  • 41. 41 be implemented (Ross, 1998). Vuong (2012) regarded the finite element method as one of the most prominent methods to solve partial differential equations. FEA can be used to solve many complex shapes with lower computational time than other methods. However, as the problem gets more and more realistic, the computational time may go up or it may be difficult to obtain a solution (Vuong, 2012). Apart from this, any error in inputs from the user may lead to incorrect solutions, which the designer may overlook (Roylance, 2011). 3.1.2. Design Criterion – Distortion Energy Density Criterion There are a number of design criteria that can be used in the finite element study. In this study, the Distortion Energy Density Criterion or Von-Mises Criterion has been used as the design criterion. Boresi & Schmidt (2003) stated this theory as the occurrence of yielding of a material when the distortional strain-energy density being equal to that of a material under uniaxial compression (or tension). Total strain energy (Uo) can be split into 2 parts – strain energy causing volumetric change (Uv) and strain energy causing distortion (UD) (Boresi & Schmidt, 2003). Mathematically, this can be expressed as, ( ) ( ) ( ) ( ) The first expression on the right hand side denotes the strain energy causing the change in volume and the second expression denotes the distortional strain energy. 3.1.3. About the software The study of stresses on the structures was done using the SolidWorks 2012, a modeling and simulation software developed by Dassault Systèmes, France. SolidWorks 2012 is feature-packed software used popularly for three-dimensional modeling of components as well as assembly. The software also allows the user to execute a finite element study
  • 42. 42 of the modeled components/assembly. It also allows the user to choose the type of study like static, thermal, nonlinear, buckling, fatigue etc. (Help.solidworks.com, n.d.). The static study of the components involves a basic study of calculating the displacements, stresses, strains and resultant forces when the component/assembly is subjected to a load (Help.solidworks.com, n.d.). SolidWorks simulation incorporates two types of finite element solvers namely FFEplus and the direct sparse solver. FFEplus is the iterative type of solver, which is used primarily as it is a faster solver and can be used in studying non-linear problems. The direct sparse solver is used in the case of multi-area contact problems (Help.solidworks.com, n.d.). 3.2. Selection of Material for the structure Selecting the material of the structure plays a very important role in the mechanical design. The material chosen should acquire various characteristics before it can be considered for the design exercise. Availability, machinability, low-cost, lightweight, high yield strength, minimum thermal conductivity etc. are some of these characteristics. Two materials were chosen for analysis – AISI 1020 steel (Cold rolled) and Aluminum 1060 Alloy. Properties of these two materials are listed in table 6. Material Properties Name AISI 1020 Steel, cold rolled Aluminium 1060 Alloy Yield Strength (N/m2 ) 3.5 x 108 2.75 x 107 Tensile Strength (N/m2 ) 4.2 x 108 6.893 x 107 Elastic Modulus (N/m2 ) 2.05 x 1011 6.9 x 1010 Poisson's ratio 0.29 0.33 Density (kg/m3 ) 7870 2700 Shear Modulus (N/m2 ) 8 x 1010 2.7 x 1010 Thermal Coefficient (/K) 1.17 x 10-5 2.4 x 10-5 Table 6 - Material properties (Source: SolidWorks 2012 material library)
  • 43. 43 3.3. Modeling Before progressing to the improvements suggested, a brief overview of the existing model is discussed. The engine in question was the SR-30 by Turbine Technologies Ltd. The existing model of the structure (shown in Turbine Technologies ltd, 2007) was modeled and studied using SolidWorks. A simulation study on this model revealed that the application of thrust on the structure would deform the structure by an approximate 1mm. The engine was mounted only on one leg, which resulted in improper thrusting of the engine against the load cell. As a result, the thrust reading would not be accurate. This meant the replacement structure had to allow the horizontal movement of the engine so that the load cell could be engaged. A university edition of the Olympus HP was procured from AMT Netherlands and replaced the SR-30. The specification of this engine is given in the datasheet (AMT Netherlands, 2009). A range of designs is presented in this section to allow mounting of the Olympus. The objective of the design was to make sure there was unobstructed movement of the engine so as to produce accurate thrust readings and incorporate instrumentation to make the experimental setup more practical and easier to use. Before the modeling phase was started, rough dimensions of the test floor were recorded. The engine had to be positioned in such a way that the centerline of the jet engine exhaust coincided with the centerline of the exhaust duct in the laboratory ventilation/extraction system. The centerline of the exhaust was 310mm from the floor of the existing test frame. Therefore, the structures were to be designed such that the centerline of the jet engine exhaust was located 310mm above the floor level. The modeling phase followed an orderly sequence of steps, which was then analyzed using the simulation feature in SolidWorks 2012. The steps are as follows: 1) Individual parts are modelled in 3-dimension form.
  • 44. 44 2) An assembly of the structure is built using the individual parts. 3) Any restrictions to the moving parts are applied to make the model realistic. 4) A simulation study is created (static study) by defining the sensor type, which is used to monitor the quantities of results in a part of a body or the entire body. The design criteria are also chosen as a property of the sensor (Help.solidworks.com, n.d.) 5) On defining the sensor type, the static study is further defined by fixtures and the loads acting on the body. Different types of fixtures can be chosen – Cantilever type, roller supports etc. SolidWorks also allows the user to define the type of loading (Force, Torque, and Pressure etc.) 6) In the simulation of an assembly, the user defines all the connections. This feature assists in the execution of the simulation and also calculates the reaction forces at each of the connectors. Springs, bolts, pins, links, welds and bearings are few of the connectors that can be used in the CAD package. 7) Once the connectors are defined, the model is ready to be executed. Execution of the model breaks the model into very small, finite elements, which are further analysed. 8) Plots of Von Mises stress in the model, strain and displacement of the model are obtained which can be used for further analysis. This step is discussed in the next chapter. An optional plot of factor of safety in the design can also be obtained. Keeping these steps in mind, multiple designs were created for the mounting structure. Following is a detail on these different mounting methods conceptualized to mount the Olympus HP.
  • 45. 45 3.3.1. Design 1 The first mounting technique resembles the method used by Léonard et al (2009) at the University of Liège. A lower base plate is suspended using four, high tensile strength wires which are connected to a frame secured to the test floor. A single block of metal acts as the leg, which is bolted to the aluminum plate on which there is an upper base plate mounted. Four pillars of about 110mm length are fixed to the upper base plate. The engine is mounted on these four pillars and secured with 4mm bolts. Essentially, the legs, upper base plate and the pillars rest on the lower base plate, which is suspended from the frame using steel cables. Figure 3-1 illustrates the first alternative. Figure 3-1 (a) Exploded view of design 1 (b) Schematic arrangement of design 1 When the engine is in operation, the thrust exerted is acted upon the entire assembly mounted on the lower base plate, suspended from the frame. This thrust results in a horizontal movement of the lower base plate over a very small distance. The wire suspension system would mean that the base plate would start to rise if it was free to move. A strain gauge type load cell assembly mounted on the test floor stops this movement and the deformation in the cell is converted to the thrust reading.
  • 46. 46 3.3.2. Design 2 In order to make the assembly lighter, the arrangement in the above design was altered. The weight reduction technique meant the single leg was replaced with two bent, sheet metal legs that were bolted to the lower base plate. Because of this alteration, the surface area of contact was spread across the width of the lower base plate. Taking into account the basic principle of stress in a body, increasing surface area would mean that the stress in the body goes down. Figure 3-2 depicts the second alternative of the design. Figure 3-2 (a) Exploded view of design 2 (b) Schematic arrangement of design 2 In the case of design 1 and 2, a Bowden cable arrangement can be incorporated to adjust the length of the cable and maintain horizontality of the lower base plate. The width of the lower base plate is almost equal to the gap between the legs of the frame. A small tolerance (about 0.5 to 1mm) should be given between the lower base plate and the legs of the frame. This restricts the lower base plate to move only in the axial (thrust) direction, ruling out the possibility of twisting or lifting of the plate when the engine is working. The lower base plates were suspended at 80mm from the test floor and the gap
  • 47. 47 under them was used to concealing electrical wires, the ECU and other small auxiliary equipment as well as providing a thermal shield from the radiated heat from the exhaust. 3.3.3. Design 3 The third option incorporated a linear rail-slide mechanism to allow linear movement of the engine due to thrust. The assembly comprises of a cantilever beam secured to the test floor. A rail is attached to this cantilever beam and a slider is allowed to slide on this rail. The movement of the slider is restricted to about 10-15mm so as to avoid shifting of the weight. Physically, providing a “stopper” which terminates the motion at the required point can do this. Alternatively, a load cell mounted on a pedestal can stop this. The load cell doubles up as a stopper and a thrust-measuring device. In the SolidWorks model however, this restriction of the movement is given by defining a length by which the slider moves. Hence, we do not see a physical stopper in the figure 3-3, which depicts the third design in question. The slider carries an upper base plate, which has four pillars, mounted on it. These pillars act as legs on which the engine sits. Figure 3-3 (a) Exploded view of design 3 (b) Schematic arrangement of design 3
  • 48. 48 3.3.4. Design 4 The fourth and final model is very similar to the third model discussed in the previous section. The only difference is that this model has two cantilever beams mounted on to the test floor. Likewise, there are two rail-slide mechanisms used – one on each beam. This is mainly done for better weight distribution of the engine when it is mounted. The upper base plate and the pillars are exactly the same as seen in the previous design (design 3). Figure 3-4 depicts the fourth design. Figure 3-4 (a) Exploded view of design 4 (b) Schematic arrangement of design 4 3.4. Input parameters for Simulation Before the finite element method can be carried out, the assembly is subjected to a procedure of inputting different parameters, which are essential. The sequence of this input has been discussed earlier in section 3.3. 3.4.1. Definition of Material This is the primary step in the procedure of analysis. The material for the assembly is defined in this step. This assigns the properties of the material. Properties like yield
  • 49. 49 strength, tensile strength etc. is defined. The properties and selection criteria of the material have been discussed in section 3.2. 3.4.2. Fixture & Loading details As a secondary requirement for the analysis, the fixtures and loading on the assembly is defined. Figure 3-5 shows fixture and loading details for all the design options in consideration. The green arrows denote the fixture. The fixture has been defined as the top of the lower base plate because it is suspended from the frame and the linear movement of the plate is very small (as it restrains against the load cell). This small movement is considered negligible in the analysis; hence the top of the lower base plate is treated fixed. In designs 3 & 4, the lower base plate can be treated as the test floor i.e. fixed from the bottom. Figure 3-5 Fixture and loading details on (a) Design 1 (b) Design 2 (c) Design 3 (d) Design 4 Loading on the material is defined by selecting the faces on which the load acts and entering the magnitude of the load (force). A load of 230N is applied on the faces, as
  • 50. 50 this is the maximum thrust developed by the Olympus HP (AMT Netherlands, 2009). Purple arrows denote the faces subjected to load. 3.5. Summary This chapter focuses on the preliminary part of the research such as the methodology adapted in executing the research, an overview of the software used, method adopted in selection of material for the structure and Computer aided modeling. This chapter also emphasizes on the design aspect of the research such as the theory behind the analysis and the method of analysis. A brief insight on the arrangement of different models followed by the input parameters for the simulation is outline in this chapter. The next part of the research gives detailed information on the type of simulation carried out, the input data on the simulation study and the behavior of these models under the action of loads. Results are presented for each model and discussed. Issues pertaining to maintenance, safety and practicality of the structure are also discussed.
  • 51. 51 Chapter 4 RESULTS AND DISCUSSION The previous chapter briefly focused on the theories involved in design, the methodology of design and also the four models that were developed for analysis. In this chapter, an elaborated process of the simulation and design is presented which is followed by the results of these simulations. Before showing the results, the arrangements for the measurement of thrust are discussed. 4.1. Thrust Measurement Measurement of thrust is a vital step in analyzing the performance of any jet engine – be it small scaled or the actual aircraft engine. The thrust measurement assembly in the old setup was not reliable enough; as a result giving inaccurate thrust values. Using a strain- gauge type load cell is the simplest and most accurate way of obtaining the thrust developed by the engine (Hafizah et al, 2012). The arrangement of the load cell depends on the arrangement of the structure. In the case of the first two designs (design 1 and 2), it is proposed that the load cell be mounted on the test floor. This allows the suspended lower base plate to press against the load cell, thus giving the thrust output. In the case of design 3 & 4, the upper base plate is the moving part, which carries the load of the engine. Since the upper base plate is at a height of about 215mm from the test floor, the load cell may have to be mounted on a pedestal or a cantilever for the upper base plate to act on it. This arrangement allows the load cell to be closer to the centerline of the engine, which is similar to the arrangement used by Callinan & Hikiss (2002).
  • 52. 52 4.2. Simulation results As the main objective of the research, which is to design a suitable test rig for the Olympus HP small-scale jet engine, the results of the finite element analysis of the four designs are presented in this section. On each design, two studies are carried out – first study being AISI 1020 Steel as the material and the second study with Aluminum 1060 alloy as the material. With the loads and fixtures in place, the program is executed. The assembly is broken into finite elements, thus generating a meshed model. The results are generated in the form of plots showing the Von-Mises stress, displacement and strain in the model. The maximum and minimum points of these parameters also form a part of the result. The results for the first half of the study i.e. with material AISI 1020 steel are given below. Figure 4-1 Von-Mises stresses in (a) Design 1 (b) Design 2 (c) Design 3 (d) Design 4 – AISI 1020 Steel material
  • 53. 53 Figure 4-2 Displacements in (a) Design 1 (b) Design 2 (c) Design 3 (d) Design 4 – AISI 1020 Steel Material Figure 4-3 Strains in (a) Design 1 (b) Design 2 (c) Design 3 (d) Design 4 – AISI 1020 Steel material
  • 54. 54 The same procedure is now repeated for all the four cases with using Aluminum 1060 alloy as the material for the structure. The density of aluminum is about 35% of that of steel (table 6) hence, aluminum is a lighter material compared to steel, which makes it easy from the handling point of view. Machinability is also an advantage as aluminum is much softer than steel (Boresi & Schmidt, 2003). Adding up all the plus points, aluminum makes an ideal material to be used for the structure. Having completed the analysis with aluminum as the material, the results are obtained. Although the yield strength of aluminum is much lower than that of steel, the Von-Mises stress in all the four designs is much lower than the yield strength of aluminum. This is shown in figure 4-4. Displacement and strain are also well within the allowable region as they are of the order of 10-3 mm and 10-5 respectively. The displacements and strains in the four designs are shown in figure 4-5 and 4-6 respectively. Figure 4-4 Von-Mises stress in (a) Design 1 (b) Design 2 (c) Design 3 (d) Design 4 – Aluminum 1060 Alloy
  • 55. 55 Figure 4-5 Displacements in (a) Design 1 (b) Design 2 (c) Design 3 (d) Design 4 – Aluminum 1060 Alloy Figure 4-6 Strains in (a) Design 1 (b) Design 2 (c) Design 3 (d) Design 4 – Aluminum 1060 Alloy
  • 56. 56 The results obtained in both the studies can be summarized and tabulated as shown in table 7. AISI 1020 Steel Aluminium 1060 Alloy Max Von- Mises stress (N/m2 ) Max Displacement (mm) Max Strain Max Von- Mises stress (N/m2 ) Max Displacement (mm) Max Strain Design 1 798844 0.00368 2.31x10-6 829625 0.00464 7.35x10-6 Design 2 3460000 0.0032 1.13x10-5 3455000 0.00747 3.46x10-5 Design 3 2101340 0.01513 5.15x10-6 2034200 0.03125 1.55x10-5 Design 4 1785690 0.00297 4.76x10-6 1724180 0.00832 1.47x10-5 Table 7 Summary of results With the given material combination and the loading, fixture details, all the designs are feasible to be adopted as the structure for mounting the Olympus. This may be the primary requirement, if not the only one. Apart from the capability of the structure to take the load and restrict deformation, factors like maintenance, reliability, and safety also come under the spotlight. This is discussed as a separate section. 4.3. Other Parameters Periodic maintenance is a must for any mechanical structure, which is subjected to a rugged atmosphere. Here, the structure is often exposed to temperature and fatigue loading. As the engine would be operated often, it could be subjected to fatigue loading. Subjecting an object to repeated load, over a period of time, causes fatigue failure. According to Campbell (2008), fatigue is caused by three factors – high tensile strength, high frequency of loading and large variation in the applied load. However, the loading in our structure does not satisfy any of these three factors. This is because the frequency of load application is not large enough, variation of the load is marginal and the Von-
  • 57. 57 Mises stress induced in the assemblies is small compared to the tensile strength. Thus, failure due to fatigue can be ruled out. In an inevitable circumstance of having to dismantle the setup, it has to be easy and convenient for the operator to solve the problem and get the setup back into use. As seen in design 1 and 2, the Bowden cable with locking nut not only maintains horizontality, but it is also easier to mount/dismount the lower base plate. If the engine has to be dismounted off the lower base plate, the Bowden cable can be used to lower the base plate and thus making it easier to access the mechanical connections. The height of the pillars has been restricted to 110mm. This is to avoid distortion of the pillar due to torque. We know that torque is a product of force and the perpendicular distance. Therefore, as the height of the pillar increases, the magnitude of torque increases. The height of the frame has been restricted to 110mm to avoid the risk of the frame heating up due to the radiation from the exhaust of the engine. As a precautionary measure, a thermocouple may be installed at the end of the frame to monitor the temperature at the back end of the frame. In the case of design 3 and 4, frequent maintenance would be a concern. As these designs involve the linear slider mechanism, it may need frequent lubrication to maintain minimum friction and hence a smoother linear motion. Since the linear motion is restricted to a very small length, the assembly will have to be dismantled when the rail needs lubrication.
  • 58. 58 Chapter 5 INSTRUMENTATION IMPROVEMENTS The previous chapter focused on different designs and their behavior upon the action of load. A brief insight was given on the maintenance and safety of these designs. This chapter gives an insight on the possible improvements that can be executed from the instrumentation point of view, which is the second-half of the objective. From the beginning, feedback and control has been an essential tool for a jet engine (Spang III & Brown, 1999). As it is a complex system operating at high temperature and pressure conditions, jet engines require close monitoring to ensure safe and cost-effective operation (May et al, n.d.). With the purpose of continuously monitoring the physical state, jet engines are equipped with computers that help in controlling their operation. The Olympus HP comes with an inbuilt ECU, which monitors the EGT and the engine speed. The ECU makes sure that the engine does not exceed the engine speed or EGT beyond a prefixed point (AMT Netherlands, 2008). A detailed connection diagram linking the ECU with the engine can be found in the user manual of Olympus HP (AMT Netherlands, 2008). The university edition of Olympus HP comes with extra measuring points allowing the operator to measure the parameters extensively and facilitates a detailed study of the engine performance. These extra measuring points cover static and total parameters (temperature, pressure) at appropriate points in the engine to best represent the thermodynamic cycle (Amtjets.com, 2011). With improper shielding of the thermocouples, the temperature values may be affected and hence the calculation of efficiency values of the turbine and compressor may not be accurate (Callinan & Hikiss, 2002). Employing multiple sensors placed along the circumference at critical stations like the turbine inlet and the exit of the turbine could be a solution to overcome this problem (Bakalis & Stamatis, 2011).
  • 59. 59 Apart from these control and measurement features, third party elements can be incorporated and linked to the data acquisition system to obtain different parameters. Thrust measurement has already been discussed in the earlier section (section 4.1.). Fuel flow rate can be measured using different ways. The most commonly used method is by using an impeller, or turbine, type flow meter, mounted in between the engine inlet and the fuel pump. This is a reasonably accurate way of measuring the fuel flow rate, as it is accurate to 1%. In this method however, the impeller of the flow meter may wear out over a period of time and the viscosity of the fuel also matters in the operation (Walsh & Fletcher, 2008). Alternatively, a visual way of recording the fuel-flow rate can be implemented by using a stop clock and a glass bottle. However, this method is less accurate as the reading is manually recorded. In the case of small-scale jet engines, the vibration is less in magnitude. Nevertheless, from the safety point of view, techniques may be adopted to measure the vibration of the engine setup. Piezoelectric accelerometers can be used for measuring vibrations. These devices are small, rugged, convenient and suitable for use at high temperature and pressure conditions (May et al, n.d.). Vibrations may also be continuously monitored using a vibration transmitter mounted on the top of the engine casing. An electromagnetic transducer transmits a signal to the indicator and gives the magnitude of the vibration. A warning lamp may also be used for added safety (Royce Plc, 1986). Tanabe et al (2003) demonstrated the use of piezoelectric sensors to measure the vibrations in a small-scale jet engine. The EGT is a very important parameter in the operation of a jet engine. As mentioned earlier, the ECU does the job of maintaining the EGT within permissible limits, by using it as a feedback signal to control the engine. Although the ECU in the Olympus has a fail-safe feature, an automatic gas temperature control system may be provided to
  • 60. 60 keep the EGT within limits (Royce Plc, 1986). Flow-rate of air may need an accurate measurement method. Installing a calibrated nozzle at the inlet can satisfy this. Exhaust gas temperature can be measured by placing a fixed probe close to the exhaust nozzle. It has to be made sure that the probe does not protrude so much that it blocks the flow of exhaust gases. A secondary probe that is traversable along the path of the exhaust can be used to take profile measurements of the exhaust cone (Witkowski et al, 2003). A thermal imaging camera can also be installed to study the exhaust gases. The profile measurements can be recorded easily with the thermal imaging camera as compared to the traversing probe technique. The price of a thermal imaging camera however, would be a major drawback. Pressure sensors may be installed circumferentially to record the static pressure at the inlet. Airflow can then be calculated by recording the pressure difference. Léonard et al (2009) adopted this method at the University of Liège, Belgium. Alternatively, the market offers a variety of equipment that can be used to measure the flow rate of air. A Sierra 780S Flat-Trak Mass Air Meter was used by Pourmovahed et al. (2003) to measure the airflow rate on the SR-30 at the Kettering University, USA. Incorporating such equipment may not be economical, but can give accurate readings. Measuring the engine speed is also a very important step in analyzing the performance of the engine. The literature already has many different methods of measuring the engine speed. The most common and accurate method would be the use of a Hall effect sensor and a magnetic pickup. This method is suitable for small-jet engines and has been incorporated by Tanabe et al (2003); Juste et al. (n.d.) and Leong et al (2004). An alternative to this method would be the use of a small generator driven by the engine, which indicates the engine speed through a visual indicator (Royce Plc, 1986). The second method however, would require major alterations to the engine which can be a
  • 61. 61 tedious job and expensive. Also anything that is powered by the engine would affect the engine and interfere with any set points within the ECU to control the engine operation. Since the engine speed is also a parameter, which cannot exceed a permissible limit, a warning lamp may be provided for the same (Royce Plc, 1986). The addition of a fuel gauge to measure the level of fuel in the tank may be a useful addition. A gas analyzer can be implemented to study the emissions from the engine. A virtual simulation analysis of the rotating components can be studied using commercially available CAD software. Linking the data acquisition system to the simulation software would be handy in importing the data. Leong et al (2004) used a similar technique to study the performance of the engine and compare it to the results from the manufacturer. Real-time simulation can be used to compute the performance of the engine based on the inputs from the data acquisition system. These results may be compared to the theoretical results obtained by the students or the results from the manufacturer of the engine to verify the accuracy in results.
  • 62. 62 Chapter 6 CONCLUSION AND SCOPE FOR FUTURE WORK 6.1. Conclusion Looking back at the literature in this we can understand that there are several ways of mounting the small-scale jet engines and there are plenty of techniques to measure different parameters. One such small-scale jet engine along with a test bench which has adequate facilities to measure different parameters and using a data acquisition system would be an ideal platform for any researcher to get acquainted with the theory of jet propulsion and study the performance a jet engine (Léonard et al, 2009). With the procurement of an Olympus HP E-start engine for the engine test cell, students at the School of Mechanical, Aerospace and Civil Engineering are sure to find it easier to understand the basics behind jet propulsion. The literature mainly focuses on the experiments carried out in different academic institutions across the globe. No part of the literature discusses primarily on the design of the test rig for small-scale jet engines. As mentioned in section 1.3, the primary objective of the research was to look at the literature and design an appropriate test rig to mount the Olympus HP jet engine. The old setup had problems with measuring the thrust, as the engine was unable to transfer the load onto the load cell. This was because of distortion in the mounting structure, making it less responsive to the thrust developed. Designs were developed based on the literature and also some knowledge on the requirements for a useful design. These designs were studied using a finite element package and the solutions were drawn out. Design 2 was found to be the optimum of the four designs because of the engine being mounted on a suspended lower base plate arrangement, which meant it was responsive to the thrust generated. The stresses generated in this arrangement were within the acceptable limits (Figure 4-4). The use of
  • 63. 63 two sheet metal legs as against one block (as in design 1) allows better weight distribution. This design is a modified version of the structure used by Léonard et al (2009). From the instrumentation point of view, the Olympus HP comes with prefixed extra measurement points for pressure and temperature, mainly designed for usage in universities as an educational tool (Amtjets.com, 2011). We have looked at various ways of measuring parameters like flow rates of air and fuel, engine speed and other parameters like vibration in the equipment. Studying the engine would give a clear idea about the limitations involved in assumptions and approximations made in analytical performance (Leong et al, 2004). As used by Bakalis & Stamatis (2011), placing circumferential temperature sensors can be considered to get an average temperature reading at the station and also to plot a profile of the temperatures along the circumference. 6.2. Scope for future work Jet propulsion education being a fundamental topic in aerospace education, the small- scale jet engine is being used as an important experimental tool by many universities across the globe. The above study can be carried forward to optimize the design in terms of minimizing the plate thickness to reduce the weight of the entire structure. To get a visual idea of the operation of the engine, a CFD study can be carried out on the whole engine or on specific components like the compressor, combustor and the turbine. This study has considered the surroundings of the engine to be in ambient condition. However, this is not the case in real. Heat may be transferred to the mounting structure through conduction, convection or by radiation. Thermal stresses induced in the structure may be studied by placing thermocouples around the test rig to record the temperature due to the heat transfer mechanisms. Additional test rigs may be developed to study the gas concentrations at different points around the engine and relate it to the
  • 64. 64 local temperatures. As a long-term development, forced airflow around the engine could be used to simulate the behavior of the jet engine during flight.
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