Pre-Swirl Augmented Vertical Axis Wind Turbine

Pre-Swirl Augmented Vertical Axis Wind Turbine
Spencer Boyajian
Charles Pecora
Christopher Sullivan
Advisor: Dr. Zha

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Table of Contents
Abstract 2
Objectives 3
Background 3
Significance 7
Design & Study Approaches 8
Results & Analysis 10
Conclusions 20
References 21
Appendix I 22
Appendix II 24
Appendix III 29

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Abstract
The vertical axis wind turbine (VAWT) has historically fallen short in cost
effectiveness and performance to the horizontal axis wind turbine (HAWT). Despite
some advantages like compactness and simple installation, vertical axis wind turbines
have been abandoned in favor of the higher power output and lower relative cost of
horizontal axis turbines. The pre-swirl augmented vertical axis wind turbine concept
originally envisioned by Dr. Gecheng Zha has achieved a power coefficient of 35% when
large prototypes were fabricated and tested at high wind speeds, proving the design to be
comparable to a horizontal axis wind turbine. Thus, it can be seen that the innate
compactness, lightweight, and simple installation of the vertical axis wind turbine can be
utilized without compromising power.
Stages of analysis, assembly, and testing were performed on the wind turbine to
establish proof of concept and determine the base performance of the design. Research on
past work with vertical axis wind turbines provided insight as how to increase the
efficiency of a VAWT while keeping scalability in mind. Mechanical improvements were
made to the design to ensure maximum efficiency and reliability prior to investigating the
fluid mechanics involved with the physical prototype. The base efficiency of the turbine
was experimentally determined to be 14.16%. Using velocity triangles, the relative wind
angle incident on the rotor airfoils was estimated. This information, combined with a
computational analysis of the airfoil shape utilized in this design, allowed for the
determination and implementation of an optimized blade orientation for the prototype.
The experimental results showed a 57.15% increase in power output, and an aerodynamic
efficiency of 22.25% with the changed blade angles.
An examination of the viability of materials other than the carbon fiber parts used
in the prototype revealed that aluminum 3003 sheets offer a much cheaper design with
almost identical performance, the only downside being less durability. However, it is
important to note that this lesser durability is still enough to withstand normal turbine
operations. In order to examine how this design would compete with turbines currently
on the market, a cost analysis was conducted using aluminum 3003 as the primary design
material. The cost per watt of power was found to be $8.42. The optimized wind turbine
design was determined to have a lower cost per unit power and higher efficiency than
similarly sized wind turbines.

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Objectives
The objective for this senior design project was to apply the concept of a pre-swirl
augmented vertical axis wind turbine and to improve its economic viability. The design
was patented by Dr. Gecheng Zha in 2011, and a second-generation prototype model was
fabricated and provided for testing, analysis, and optimization.
The main goal of this project was to use this vertical axis wind turbine design to
achieve a cost effective and versatile method of harnessing wind energy. In order to
achieve this goal, the turbine’s power output needed to be maximized while
simultaneously minimizing the cost of the turbine. The completion of this goal was
assessed by comparing the resulting design’s power output and cost per watt to similarly
sized wind turbines.
Further analysis was then conducted to investigate the ways in which this design
can be scaled to a greater size and resulting power output with similar performance, in
addition to determining ways in which cost of production can be cut without significant
loss in performance.
Background
Increased awareness of the negative environmental impacts of non-renewable
energy sources has lead to an increased demand for renewable energy technologies. Wind
energy is renewable and essentially infinite source of energy. Unfortunately, the energy
available varies with the wind speed. Vertical axis wind turbines have great potential due
to their simple and compact design. Currently, the relatively low efficiency and energy
output per unit of power of vertical axis wind turbines makes them unattractive as an
energy option because they take longer to pay for themselves. However, they can be
easily placed on top of existing structures minimizing installation costs. This design
project will focus on a newly patented design that is a Darrieus type VAWT.
Figure [1] The three types of VAWTs [1]

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Previous work:
As of late 2012, Sandia National Laboratories is undertaking a project to test the
feasibility of vertical-axis wind turbine architecture for large-scale deployment in the
offshore environment. This idea is currently being tested at Sandia National Laboratories
in New Mexico. The goal is to reduce the biggest barrier to offshore wind development—
high cost of energy (COE)—by 20% or more through the application of VAWT rotor
technology. The research project will:
 Develop innovative VAWT rotor designs that result in cost-effective and easily
manufactured rotors for deep-water offshore machines
 Demonstrate the potential for greater than 20% reduction in COE for deep-water,
floating VAWT systems
 Develop specialized manufacturing techniques, certification test methods, and a
commercialization plan for offshore VAWT rotors
 Test, in a wind tunnel and combined wind-wave tank, a proof-of-concept
subscale, deep-water floating offshore wind-turbine generator employing a
VAWT rotor [2]
The Department of Mechanical Engineering at Dalhousie University had a project
in 2005 on VAWT with concentration on the issue of some VAWTs not being self-
starting. Meaning the turbine must be brought to a certain operational speed before it will
capture enough wind energy to rotate on its own. Their project involves varying the pitch
of the blades (passively and actively) but due to increased complexity, the failure rate,
maintenance required, and parts required became cumbersome. Since 2005, self-starting
wind turbines have been developed with simpler ideas but again efficiency suffers. This
publication is useful for deciding what methods of improvement are worth researching.
The publication's results indicate that the benefits of active blade pitch control are
negated by high failure rates, maintenance requirements, and overall cost of production,
thus indicating that a fixed-blade approach is more appropriate for this design.
The most useful information for our design optimization comes from the WPS
International Report written by Dr. Zha [3]. This paper includes information regarding
number of blades, both stator and rotor, and their effects on the power coefficient for this
turbine style. The wind tunnel testing and analysis that followed indicated that a lower
number of larger rotor blades could yield higher efficiencies. In addition, this paper
serves as a proof of concept for this stator blade design. Furthermore, it has information
regarding the flow interaction with the turbine and where losses are most apparent. For
example, the stator blade angles were very high in their initial tests and were found to be
too large with respect to the inner blades. Our design will explore and test the effect of a
higher rotor chord to stator chord ratio and a decreasing number of internal blades. The
CFD work detailed in this paper showcases the high loss areas of the turbine, the center
and the rotor blades on return to the front of the turbine. This previous design uses a

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center rotor arrangement where the chords of the blades are perpendicular to the
tangential velocity direction. The current design implements CFD research on this angle
to optimize the inner blade angle, vastly improving efficiency.
Past work was also conducted on the rotor design and scalability of VAWTs as
part of a student's Master's thesis at Delft University. Information about rotor design and
optimization from this publication was used extensively in this project, as data on VAWT
became very sparse after research dropped off in the 1980s [4].
Constraints:
1 Economic: The VAWT market has a wide range of turbine designs but it is important
to remember that for a design to be useful it has to produce enough power to make the
initial investment worth it. This is a hard thing to quantify, but by using existing
examples of wind energy systems, it can be determined whether or not this design can
compete. In the renewable energy business, the success of the product is a function of
how quickly the system can pay off the initial investment. Solar energy, for example, can
take up to 10 years to pay off the overhead costs. Increasing the power output of this
turbine design will make it more attractive to consumers. However, for military
applications, the use of more expensive materials such as carbon fiber to reduce factors
such as weight and the radar signature, but will increase these costs. The average cost per
kW in wind turbines under 100kW is roughly $3000-$8000 per kilowatt of capacity [5].
Therefore, this turbine must be competitive with these prices in order to be considered
practical. Keeping the maintenance costs down is also essential to keeping the design
competitive. The initial fabrication and installation of the turbine are the main costs
associated with this design.
2 Environmental: The VAWT poses little environmental impact, as its purpose is to
produce clean renewable energy. The materials used in its construction are not hazardous
to the environment and its main application would be in locations where horizontal axis
wind turbines are impractical, such as the roofs of buildings, on top of skyscrapers, and
above other small structures.
3 Social Impact: There are few social constraints on VAWTs as they are generally
accepted as a popular alternative to fossil fuels. Although there is some aversion to large
wind energy systems due to their size, noise, and visual disturbance, this design is more
compact and versatile, being able to utilize spaces otherwise wasted such as the roofs of
tall buildings. These areas are out of sight and should not produce any social impacts.
4 Political: This project has relevant political constraints, most of which can be seen in a
positive light. For example, renewable energy systems are subsidized such that a
percentage of their initial cost can be refunded via tax deductions. This makes entering
the market easier as the cost of a wind turbine can be subsidized, making it a more
attractive option for the consumer. This may change in the future as renewable energy
systems become cheaper and the subsidization decreases.

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5 Ethical: Ethical constraints will not affect this design.
6 Health and Safety: The safety constraints of this design include design codes and
standards for the materials used in the design. Safety issues regarding materials must be
taken into account to ensure that the product will be operating with high enough safety
factors to prevent failure. Additionally, a problem wind turbines have is bird kills, which
occur when birds cannot see the path of the spinning blades of wind turbines and the
turbine strikes them. This is a problem for horizontal axis wind turbines, but because this
design utilizes stator blades that surround and clearly define the swept area of the rotor
blades, it is unlikely that birds will fly into the kill zone.
7 Manufacturability: This design is subject to manufacturability constraints as it uses
many unique parts, such as the custom high-camber airfoils and the plates to which they
attach. Carbon fiber is very tricky to implement in a design due to the high risk of brittle
fracture at attachment points. Using aluminum can help keep costs low, as using sheets to
mold the airfoil shapes is a less expensive process than fabricating a composite material.
For military applications, the use of carbon fiber in the design may introduce more
difficulty in manufacturing but, by using one mold each for the stator and turbine blades,
the feasibility of manufacturing remains optimal. An aluminum design eliminates the
need for fasteners, as the sheets will have fold-over tab and slot joints. By using
Aluminum 3003, the favorable ductility needed for bending the sheets around the airfoil
profiles is retained. This type of aluminum still has favorable erosion resistance
properties even before the application of the 3M™ Wind Protection Tape.
8 Sustainability: Our design is not affected by sustainability constraints, as wind turbines
do not produce harmful by-products.
9 Codes and Standards: In Miami-Dade County there are no specifications for renewable
energy systems such as wind turbines and, therefore, all building codes and regulations
apply. The codes affecting this design can be found in the “Miami-Dade Sustainable
Development and Building Code: Project Code Diagnosis Report and Priority
Recommendations” [6]. “Standards for Wind Energy Systems in Urban/Suburban Areas”
also contains details specific to building wind energy systems that apply to this design
[7]. Some of these constraints include zoning regulations, noise regulations, height
parameters, electrical codes, and turbine appearance codes. This design falls well within
the size constraints and noise constraints set forth and the remaining electrical codes rely
upon where this turbine will be implemented. The turbine appearance requirements are
met as well utilizing the 3M™ Wind Protection Tape, with these requirements being that
the blades are a neutral color (gray satisfies this clause).

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Significance
Improving VAWT technology allows us to make another step closer to breaking
dependence on fossil fuels. This project proves the pre-swirl concept is a great method to
increase efficiency in Darrieus type VAWTs utilizing high cambered airfoils as blades.
Additionally, it provides insight into how the angle of attack of the blades with respect to
the radial direction affects performance. Finally, this project leaves a path open for
further research and progress in the relatively unexplored field of vertical axis wind
turbines.
Vertical axis wind turbines are generally less expensive to manufacture and more
versatile than the wind turbine axis turbine. For these reasons, the style of turbine should
be more widespread than it is; however, it is hindered by the low efficiencies of common
designs. Typical vertical axis wind turbine efficiencies are around 8-10% with well
optimized designs around 15%, while for horizontal axis wind turbines efficiencies are
roughly 35%. According to a paper recently published by Dr. Zha, the pre-swirl
augmented vertical axis wind turbine achieved 35% energy efficiency in preliminary
testing. This turbine design is expected to have 20-40% higher power output than the
best vertical axis wind turbines on the market [7]. This pre-swirl design shows promise
and with further research could lead to great advancement in the stale vertical axis wind
turbine market.
If this sort of power output is achieved and the design is made to be cost
competitive with similar horizontal axis wind turbines, then the significance of this
project would be great. A vertical axis wind turbine is versatile, as it can easily be
installed without high poles or masts for elevation. It can also be installed on rooftops
and in tight quarters. Its footprint when viewed from above is only a circle versus the
footprint a horizontal axis turbine makes, the diameter of the turbine as a whole. For this
reason, this design could make wind energy more attainable in urban environments and
on smaller scales than the vast wind farms in the countryside. The company working
with Dr. Zha on this design previously had hoped to market the turbine to the Department
of Defense. For this reason, they have high interest in increasing the efficiency of the
turbine to increase the amount of power the turbine is capable of producing.

8
Designand Study Approaches
Figure [2] Preliminary design assembly and cross section
The figure above shows the preliminary design for the vertical axis wind turbine
with the number of outer stators blades installed varying. The eight small blades around
the outside of the turbine are the stator blades. These redirect the flow to maximize the
amount of energy that can be absorbed from the wind. The rotor blades are the three
internal blades. The specifications for the blades and their airfoils are listed in Table [1].
The orientation angle listed refers to the angle between the radial direction in the turbine
and the cord of the airfoil.
Cord Length (mm)
Thickness
(%) Camber (%) Orientation (°)
Stator 105 20 15 30
Rotor 218 20 26 6
Table [1] Given Airfoil Specifications
The airfoils are arranged in the manner shown in Figure [1], resulting in a design
with a frontal rectangular cross section. The height of the turbine used for testing is
0.762 meters and the outermost diameter of the turbine is 0.662 m. This gives the turbine
a cross section of 0.504 m2.
The prototype model provided for testing and optimization was made using a
woven, unfinished carbon fiber for blade construction. Although light, the cost of
manufacturing can be quite high. The low weight, and thus moment of inertia should
allow for a reduced starting wind speed. The prototype shaft used for driving the

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generator is made of aluminum 6061-T6. The generator itself is a 200-watt low-torque 3-
phase generator that was provided by Dr. Zha specifically for the testing of the turbine
prototype. The generator is hooked up to a rectifier setup that was wired in order to test
the power output through a dummy load. Resistors ranging from 0.47 Ohms to 200 Ohms
were used.
The original prototype came with bearings, but these were found to be far too
inefficient for use with this design. Because of this, bearings designed for use with low
rpm, light load capability, and a sealed bearing chamber for outdoor use were required.
The ReliaMark UCF205-16 RM Ball Flange Unit Bearings were selected to replace the
old bearings. These replacements have a lower load capacity, but this translates into a
lower force required to spin the bearing. A smaller force required to spin the bearings
also means a lower cut-in wind speed and less rotational drag for the turbine. The turbine
was dismantled and bearings replaced. Unfortunately, due to funding issues only metal-
housed bearings could be acquired, as opposed to the thermoplastic housed-bearings
included in the original design to reduce radar signature in military applications.
When wind-tunnel testing for this turbine, a number of measurements were taken.
Because the turbine could not fit in the small test chamber of the wind tunnel, the turbine
was placed in the exhaust flow section of the tunnel, where wind speed varied
substantially. It was therefore imperative that accurate wind speed measurements were
conducted for each wind tunnel fan frequency at which the prototype turbine was tested,
in order to accurately calculate wind energy. Wind energy can be determined as shown
in Equation [1] using wind speed Vw, air density ρ, and cross-sectional area A.
𝑊𝑖𝑛𝑑 𝐸𝑛𝑒𝑟𝑔𝑦 = 1/2∗ 𝜌 ∗ 𝐴 ∗ 𝑉𝑤
3
[1]
The power output of the wind turbine was the main conern of this project, and it
was therefore essential to develop a method to precisely and accurately determine the
turbine’s power output. To do this, the DC voltage across a dummy load was measured
using a multi-meter. The electrical power output was then calculated using the
relationship shown in Equation [2], where P is power, V is voltage, and R is resistance.
Further, efficiency was found from the ratio of electrical power output and the wind
energy.
𝑃 = 𝑉2
𝑅⁄ [2]
Despite some positive evidence from preliminary testing done by Dr. Zha, the
first test for this design was to determine whether the pre-swirl design was effective at all
in increasing the wind turbine efficiency. Initial tests examined the power output and
efficiency of the turbine with all eight stator blades. Four stator blades were then
removed, and the test repeated. Finally, the front blade was taken off, leaving three
blades on the side of our turbine facing away from the incoming wind. It was believed
that this arrangement would satisfy an effective “no-stator” setup, thus performing
similarly to the turbine with no stator blades at all. These efficiencies were compared to

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determine whether including stator airfoils increases power enough to compensate for the
added cross-sectional area.
Once the number of stator blades to be included was determined, the next goal
was to optimize the rotor blades. In order to produce the most power from our turbine,
the lift on the rotor airfoils was examined. First, the relative wind speed and angle of
attack to the inner airfoils had to be determined. From the geometry of the stator airfoils,
it was approximated that the wind enters the turbine at a 60° angle relative to the radial
direction. The wind speed and rotational speed of the rotor blades were measured in the
wind tunnel and these numbers were used in a velocity triangle to determine the relative
wind speed of the rotor blades.
ANSYS Fluent was used to determine the desired angle of attack of for the high-
camber rotor airfoil shape. The standalone shape was used in the program with a range
of angles of attack, from -5° to 45°. The results obtained from ANSYS included the
forces on the airfoil in the x and y directions.
In order to maximize power output, the force on the airfoil in the direction of
rotation was to be optimized. To calculate this tangential force, the orientation of the
airfoil had to be determined for each angle of attack using the relative wind velocity
calculated from the velocity triangle. Once the orientation of the blade was determined,
the x and y components of force were converted into a single value for tangential force.
The optimal angle of attack was then determined from the greatest tangential force value.
This optimal angle of attack was then used to guide our repositioning of the rotor
airfoils. Once the blades were adjusted, more testing was done to determine the change
in power output. As this calculation relies heavily on experimental data from testing
under specific conditions, this testing and simulation procedure can be repeated in order
to optimize the turbine for any wind speed.
Results & Analysis
Upon receiving the preliminary wind turbine prototype, the severe resistance
when spinning the rotor blades was apparent. Tests were run before and after replacing
the excessively lubricated bearings. Results from the testing are shown in Table [2]. The
testing was conducted at a wind speed of 2.612 meters per second in both cases with
eight stator blades and the original rotor blade orientation, which was a 6.5° inclination.
The change of bearings resulted in a 165% increase in both power output and efficiency.
Old Bearings New Bearings
Turbine Power (W) 0.258 0.684
Efficiency 4.69% 12.43%
Table [2] Turbine power and efficiency from bearing change
After determining the baseline efficiency from the preliminary design and the new
bearings, testing was done with zero, four, and eight stator blades and the original rotor

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orientation. Due to the decreased structural integrity with reduced number of blades, the
wind speed was only set to 2.612 meters per second for testing.
Number of Stators 0 4 8
Turbine Power (W) 0.001 0.174 0.684
Efficiency 0.02% 3.16% 12.43%
Table [3] Turbine Power and Efficiency for varied number of stator blades
The results from this table indicate that the inclusion of stator airfoils in this
design is beneficial to the efficiency. The removal of stator blades from the turbine
resulted a 99.84% decrease in efficiency when compared with the eight-stator blade
configuration. The four-blade arrangement resulted in a 74.59% decrease in efficiency.
The fact that the no blade arrangement fared so poorly is not surprising considering that
the rotor airfoils are shaped and oriented in a way that is meant to capture energy from
the wind after it has been swirled. From this testing, it was determined that an eight-
blade configuration would be the most efficient for our vertical axis wind turbine design.
Once the pre-swirl concept was experimentally proven to increase efficiency, the
next aim was to optimize the power output using aerodynamic analysis. In order to
understand the relative wind speed to the rotor blades, the wind speed, wind direction,
and rotational speed of the blades was measured. These measurements are in Table [4].
Also, Figure [3] depicts a representation of the velocity triangle and vector addition.
V wind Wind Angle Rotor speed V relative Relative Angle
Leading Edge 3.38 m/s 60° 4.59 m/s 2.37 m/s -44.9°
Trailing Edge 3.38 m/s 60° 1.22 m/s 2.40 m/s 45.22°
Table [4] Relative wind speed and angle calculations for base design
Figure [3] Velocity triangle for relative wind speed to rotor blade
The results shown in Table [4] suggest that there is a variable angle of attack
along the length of the rotor airfoils. The leading edge was found to have a negative
relative wind angle and the trailing edge a nearly equal and opposite relative wind angle.

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This is due to the fact that the leading edge rotates faster than the trailing edge. This
result was used to estimate that the mean relative wind angle is roughly 0°. Using this
information, we conducted analysis assuming that the relative wind incident on the rotor
blades travels along the radial direction.
With this information, flow over the rotor airfoil shape was simulated using
ANSYS Fluent. Simulations were done with a straight flow of 5 meters per second wind
speed at varied angles of attack, shown in Figure [4]. In the figure, the net tangential
force is plotted against the angle of attack. The net tangential force was calculated in the
direction of rotation from the x and y components of force, which were obtained from the
output of the Fluent simulation. The orange data point indicates the preliminary angle of
attack data point, and the green data point indicates the ideal angle of attack.
Figure [4] Plot of net tangential force versus angle of attack
Figure [5] shows a contour plot of the static pressure around the airfoil obtained at
the ideal angle of attack of 25°. Using this optimized angle of attack, it was determined
that the power coefficient of the turbine could be increased by rotating the rotor airfoils.
New holes were drilled to align the airfoils at roughly a 25° inclination from the radial
direction. Based on the relative velocity calculations, this would allow for a 25° angle of
attack and a maximized power output.
0
2
4
6
8
10
12
14
16
-10 0 10 20 30 40 50
NetTangientialForce(N)
Angle of Attack (degrees)

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Figure [5] Contour plot of static pressure with a 25° angle of attack and 5 m/s wind speed
The optimized blade orientation was then tested in the same conditions as the
preliminary design was tested, with a 3.383 meters per second wind speed. The
comparison of power output and efficiency is shown in Table [5].
Rotor Blade Angle 6° 25°
Turbine Power (W) 1.693 2.660
Table [5] Turbine power data before and after optimized blade orientation
Results from Table [5] indicate the success of the rotor blade angle optimization.
The change resulted in a 57.15% increase in both power and efficiency. Figure [6],
below, shows the change in blade angle from the preliminary design to the optimized
design. The inner rotor blades were rotated 19°.

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Figure [6] Preliminary 6° orientation (left) and optimized 25° orientation (right)
The final design utilizes two airfoil shapes in the configuration shown above on
the right. The specifications of the two airfoils along with their orientations are specified
below in Table [6].
Blade
Cord
Length Thickness Camber Orientation
Outer
Radius
Blade
Length
Stator 0.105 m 20% 15% 30° .381 m 0.742 m
Rotor 0.218 m 20% 26% 25° .280 m 0.712 m
Table [6] Rotor and stator blade dimensions and positions
Figure [6] Stator (left) and Rotor (right) blade models

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Figure [6] provides a view of the models of both the stator and rotor blades
created using the dimensions and specifications presented in Table [6]. The differences
in camber of the airfoils is clearly depicted in the figure.
Figure [7] Rotor (left) and Stator (right) baseplate models
The baseplate models of the stator and rotor assemblies are shown in Figure [7].
Two baseplates are required for each set of blades, one oriented above the blades and one
below, in order to provide structural support as well as an attachment point between the
upper and lower shafts and the turbine’s bearings.
Figure [8] Upper and lower shafts, respectively
Figure [8] provides models of the upper and lower shafts which, when inserted
into the turbine’s bearings attached to the stator baseplates, allow for the rotation of the
inner rotor blades with respect to the stationary ring of stator blades.

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Figure [9] Outer assembly
The model shown in Figure [9] is that of the outer assembly, formed by eight
stator blades and two stator baseplates. The bearings of the turbine are fixed on the outer
faces of the baseplates, concentric with the holes at the center of the baseplates.
Figure [10] Inner assembly

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Figure [10] depicts a model of the inner assembly of the turbine design, consisting
of three rotor airfoils, two rotor baseplates, and the upper and lower shafts. This
assembly fits concentrically inside of the outer assembly shown in Figure [9].
Figure [11] Complete assembly
Figure [11] provides an isometric view of the complete assembly. As can be seen,
the rotor assembly is in place within the stator assembly, with the upper and lower shafts
in their proper locations for smooth rotation within the bearings.
Figure [12] Connection shaft

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Figure [12] contains a model of the connection shaft that was designed and
fabricated to transfer motion from the lower shaft of turbine to the generator centered
under the turbine. As can be seen, one side of the shaft utilizes a hex-shaped male head
in order to fit into the corresponding female connector required by the generator. The
other end of the shaft was fabricated into a D-shape connector in order to be properly
fitted to the turbine’s lower shaft.
(Note: Detailed drawings of each design component, along with specifications for
material type, dimensions, and resulting weights, can be found in the Appendix III.)
The important quantity that was calculated during this design and testing was the
aerodynamic efficiency of the turbine. This value can generally be used to determine the
quality of a turbine design. While 22.25% efficiency is quite impressive for a vertical
axis wind turbine design, it is important to note that the wind used during testing was the
exhaust section of a wind tunnel rather than the test section. For this reason, the wind
speed measurements were not uniform and contained high variance. Table [7] below
shows the error analysis and a 95% confidence interval for the turbine power output, the
wind energy, and the efficiency calculations. It is important to note that this error
analysis reflects that despite the high variation wind energy, and thus aerodynamic
efficiency, the power output was accurately measured. This suggests that the results
reflecting the change in power and efficiency between designs are meaningful, although
more accurate testing is required to obtain a reliable value for efficiency.
Power Output (W) Wind Energy (W) Efficiency
Mean 2.660 11.959 22.25%
Standard Error 0.064 3.032 5.67%
95% Confidence
2.524 5.530 10.23%
2.797 18.387 34.26%
Table [7] 95% confidence interval for turbine power output and efficiency
To properly gauge how our turbine competes with the rest of the wind energy
market we have calculated an estimated cost for our design utilizing cheaper aluminum
construction versus the military-needed specific carbon fiber design. This drives down
the cost of manufacturing significantly and reveals how this design is indeed a
competitive option for wind energy.
Based on the availability of raw 1/8”, 4x10ft aluminum 3003 sheets priced at
$227.62 per sheet, it was determined that the total cost requirement for the 47 square feet
needed for the design is $267.45 [10]. Only one sheet is required with minimal extra
material. The ¾” aluminum 6061 shaft was obtained and cut to length at C&R Metals for
$7. The metal work for the blades and the end plates can be sourced to Doudney Sheet
Metal Works’ south Miami location. A verbal estimate was given for manufacturing cost
of $15 for the end plate stamping, and a further $70 to have all of the airfoil shapes
manufactured. The two ReliaMark UCF205-16 RM Ball Flange Unit bearings were
obtained from Florida Bearings Miami, a Kaman company, for $64.38. The generator is a
Permanent Magnet Generator for a Wind Turbine rated for 200W. It can be obtained

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directly from the company website for $249 [11]. A ten-piece set of Uxcell M10x20mm
Thread 304 Stainless Steel Hex Socket Bolts and associated ten-piece set of M10x1.5mm
304 Stainless Steel Nylock Nylon Insert Hex Lock Nuts, both of which are required for
assembly of the turbine, can be acquired for $8.05 and $7.70, respectively. Finally, to
satisfy aforementioned code restrictions, the turbine must have a neutral gray color. 3M
manufactures a wind protection tape specially designed for wind turbine blades and offers
great performance and erosion prevention [12]. This product is available by special order
only and ranges in price with the average cost for the protection tape required being $30
(See Appendix I for full commercial pricing information and calculations used in
determining material costs).
Item/Service Price
1/8" Aluminum 3003 Sheet, 47 ft^2 $267.45
3/4" Aluminum 6061 Shaft $7
Metal Bending/Cuts $85
Bearings $64.38
Generator, 200W $249
Wind Protection Tape $30
Hex Socket Bolts $8.05
Hex Lock Nuts $7.70
Total Cost: $718.58
Table [8] Price list of materials and manufacturing
As can be seen in Table [8], the total manufacturing cost of the wind turbine is
$718.58. Placing the turbine at a market price of $1000 results in a gross profit margin of
28.14%. Table [9] provides further cost analysis by comparing this turbine design to
other turbines of similar size. Data for both a 100-Watt horizontal axis wind turbine
made by MOLA Energy Technology Co. [8] and a 100-Watt vertical axis wind turbine
made by Qindao Bofeng Wind Power Generator Co. [9] are used for comparison. These
turbines were chosen for their comparable dimensions to our design, as cost per watt of a
turbine decreases substantially when a design is scaled up. The power output listed for
the project design is an estimate based on the experimentally obtained efficiency, as we
were unable to test above 3.383 meters per second.
Project Design Competing HAWT Competing VAWT
Swept Area (m^2) 0.5044 0.8659 0.6400
Wind Speed (m/s) 12 12 12
Wind Energy (W) 533.86 916.47 677.376
Turbine Power (W) 118.76 100 108
Turbine Efficiency 22.25% 10.91% 15.94%
Cost $1000.00 $1,000.00 $1,000.00
Cost per Watt $8.42 $10.00 $9.26
Table [9] Power and cost comparison with existing small wind turbines [8] [9]

20
The comparison shown in Table [9] implies that the project design turbine is
capable of producing more power than existing wind turbines at a lower cost per watt and
a smaller swept area.
Conclusions
Evidence that the inclusion of stator pre-swirl blades in a vertical axis wind
turbine design increases efficiency was obtained experimentally, and further optimization
was performed using fluid mechanics principles and computational analysis. After
optimization, the turbine’s power output and efficiency were increased by 57.15% when
compared to those of the base model. It was also determined that the aerodynamic
efficiency of the optimized wind turbine design was 22.25%, which suggests that the
turbine could outperform similarly sized existing wind turbines currently on the market,
both in efficiency and cost per unit power ($8.42 per watt).
This project has given new insights on vertical axis wind turbines and could
potentially lead to further improvements in this field. Future work can be done to
improve the results of this project. Perhaps most importantly, the reliability of testing can
be improved by using a wind tunnel with a test section that is large enough to house the
entire turbine, thus providing sustained, evenly distributed wind speeds. This would
likely lead to more accurate efficiency calculations and better overall performance. This
would also allow for testing at higher wind speeds, whereas current results were hindered
by wind tunnel limitations.
Furthermore, the testing and optimization methods used in this project can be
replicated for a similarly designed wind turbine of any size and any wind speed. A larger
wind turbine that utilizes the same pre-swirl concept can be optimized for high wind
speeds. In scaling up, the cost per unit power could be lowered and the cost effectiveness
of this wind turbine concept could be further improved.

21
References
[1] "Wind Energy Overview," Belarusian web portal on renewable energy,
http://re.energybel.by/en/renewable-energy-technologies/wind/
[2] Sutherland, H.J., Berg, D.E., and Ashwill, T.D., “A Retrospective of VAWT
Technology,” Sandia National Laboratories Technical Report, SAND2012-0304, January
2012.
[3] Zha, Gecheng, A Novel Concept of Pre-Swirled Augmented Vertical Axis Wind
Turbine, WPS International Report, June 30, 2015.
[4] M. Schelbergen B., "Structural Optimization of Multi-Megawatt, Offshore Vertical
Axis Wind Turbine Rotors. Identifying Structural Design Drivers and Scaling up of
Vertical Axis Wind Turbine Rotors", 2013, Delft University
[5] "How Much do Wind Turbines Cost?" Windustry.org
http://www.windustry.org/how_much_do_wind_turbines_cost
[6] "Miami-Dade Sustainable Development and Building Code Project. Code Diagnosis
Report and Priority Recommendations", Clarion Associates, August 2011.
[7] "Standards for Wind Energy Systems in Urban/Suburban Areas", Municipal Code,
2011.
[8] "H-100W Direct Drive Permanent Magnetic Wind Turbine 2,"
http://qdbofeng.en.alibaba.com/product/284869947-
209790256/H_100W_Direct_Drive_Permanent_Magnetic_Wind_Turbine_2.html
[9] "Hot selling Portable Easy To Install Mini HAWT 50W 100w diy wind power
generator," http://www.alibaba.com/product-detail/Hot-selling-Portable-Easy-To-
Install_60173084022.html?spm=a2700.7724838.0.0.DJiRHo
[10] Aluminum 3003 Sheet, Cut 2 Size Metals
http://www.cut2sizemetals.com/aluminum/sheet/ash/?_kk=aluminum%20sheeting&_kt=
cb7e6ba6-57b6-4b37-8406-
db6a5a0b1107&gclid=CjwKEAjw_7y4BRDykp3Hjqyt_y0SJACome3Tkl5_U17obhyaR
CbyoRc7oQwMmPWnFUKYdBXUqbXimhoC8Ffw_wcB
[11] Permanent Magnet Generator for Wind Turbine 200W
http://small-
generator.com/buy/index.php?main_page=product_info&cPath=1&products_id=42
[12] 3M™ Wind Protection Tape
http://solutions.3m.com/wps/portal/3M/en_US/Wind/Energy/Products/Wind_Protection_
Tapes/

22
Appendix I
Materials and fabrication costs
1/8” thick 4x10ft aluminum 3003 sheet, $227.62.
http://www.cut2sizemetals.com/aluminum/sheet/ash/?_kk=aluminum%20sheeting&_kt=
cb7e6ba6-57b6-4b37-8406-
db6a5a0b1107&gclid=CjwKEAjw_7y4BRDykp3Hjqyt_y0SJACome3Tkl5_U17obhyaR
CbyoRc7oQwMmPWnFUKYdBXUqbXimhoC8Ffw_wcB
Aluminum Cost Calculations
Component (#) stator (8) rotator (3) disk 1 (2) disk 2 (2)
Surface Area
(single) 0.18 0.38 0.3136 0.5776
Surface Area
(total) 1.44 1.14 0.6272 1.1552
sum: 4.3624 m^2
46.96 ft^2
Rate: $227.62 40 ft^2
Final Cost: $267.45 47 ft^2
Aluminum 3/4" shaft cut to length $7
C&R Metals
2991 NW North River Dr, Miami, FL 33142
Metal bending and cuts/stamps performed at Doudney Sheet Metal Works’ South Miami
location. 3020 S.W. 38th Ave. Miami, FL 33146
Verbal estimate from Adam of $85.00 ($15 for end plates stamped, $70 for airfoils).
ReliaMark UCF205-16 RM Ball Flange Unit
2X$32.19=64.38
Florida Bearings Miami (a Kaman company)
10050 NW 116th Way, Ste 1
Miami, FL 33178
Permanent Magnet Generator for Wind Turbine 200W. $249.00
Listed on http://small-
generator.com/buy/index.php?main_page=product_info&cPath=1&products_id=42
Model: YAF-200
Rated power: 200W
Max power: 220W
Rated voltage: 12/24V
Max start resisting torque: 0.35N.M
Rated speed: 450r/m

23
Max speed: 500r/m
Type: Three-phase permanent magnet generator
Working temperature: -40℃-80℃
Protection: IP54
Net weight: 3.0kg
3M™ Wind Protection tape, ~$30. Special order only.
available at
http://solutions.3m.com/wps/portal/3M/en_US/Wind/Energy/Products/Wind_Protection_
Tapes/
Product number: W8640
Color: Gray
Thickness: 0.38mm
Tensile Strength @ Break lb/in (N/100 mm): 87 (1542)
Elongation at Break (%): 500
Service temperature: -40 to 200 degrees Fahrenheit
Item/Service Price
1/8" Aluminum 3003 Sheet, 47
ft^2 $267.45
3/4" Aluminum 6061 Shaft $7
Metal Bending/Cuts $85
Bearings $64.38
Generator, 200W $249
Wind Protection Tape $30
Hex Socket Bolts $8.05
Hex Lock Nuts $7.70
Total Cost: $718.58

24
Appendix II
Excel Calculations
Constants
Load (Ohms) 0.47
rho (kg/m^3) 1.225
Area (m^2) 0.5044
No Stator Area
(m^2 0.38862
Wind Speed Measurements (m/s)
30Hz 35Hz
1 1.57 2.89
2 2.01 3.06
3 2.89 2.18
4 1.05 4.3
5 1.46 3.06
6 3.24 3.94
7 2.89 2.68
8 3.42 2.36
9 3.42 5
10 2.54 3.06
11 4.24 4.68
mean 2.612 3.383
SD 0.297 0.286
Pre-Bearing
Change
Old Bearings New Bearings
Voltage (V) 0.348333333 0.567
Wind Energy (W) 5.504400092 5.504400092
Turbine Power
(W) 0.258161939 0.684019149

25
Voltage Measurements (V)
Blade Arrangment 0 4 (6°) 4 (6°) 8 (6°) 8 (6°) 8 (25°)
Tunnel Frequency (Hz) 30 30 35 30 35 35
1 0.0143 0.292 0.552 0.561 0.901 1.124
2 0.0136 0.258 0.586 0.578 0.904 1.098
3 0.0198 0.333 0.518 0.569 0.887 1.127
4 0.0238 0.271 0.534 0.559 0.875 1.131
5 0.0285 0.275 0.551 0.566 0.895 1.111
mean 0.020 0.286 0.548 0.567 0.892 1.118
SD 0.006 0.029 0.025 0.008 0.012 0.014
Blade Arrangment 0 4 (6°) 4 (6°) 8 (6°) 8 (6°) 8 (25°)
Tunnel Frequency (Hz) 30 30 35 30 35 35
Wind Speed (m/s) 2.612 2.612 3.383 2.612 3.383 3.383
Voltage (V) 0.02 0.2858 0.5482 0.567 0.892 1.1182
Wind Energy (W) 4.241 5.504 11.959 5.504 11.959 11.959
Turbine Power (W) 0.001 0.174 0.639 0.684 1.693 2.660
Efficiency 0.02% 3.16% 5.35% 12.43% 14.16% 22.25%
CFD Analysis
5 m/s wind speed
Angle (deg) Vwindx (m/s) Vwindy (m/s) Fy (N) Fx (N)
-35 0.819152044 -0.573576436 6.6772367 4.8291441
-30 0.866025404 -0.5 8.4859605 5.1302931
-25 0.906307787 -0.422618262 10.550234 5.1790353
-20 0.939692621 -0.342020143 12.288527 4.7787545
-15 0.965925826 -0.258819045 13.438554 3.9717039
-10 0.984807753 -0.173648178 13.989815 2.9108142
-5 0.996194698 -0.087155743 14.168544 1.7877431
0 1 0 14.260908 0.59999192
5 0.996194698 0.087155743 13.022937 -0.30507365
10 0.984807753 0.173648178 11.364019 -0.90905858
15 0.965925826 0.258819045 9.9562366 -1.2077993

26
Angle (deg)
Actual Angle
of Attack
Angle to Radial
Direction from x Normal Force
-35 -5 -35 8.239555357
-30 0 -30 9.914203919
-25 5 -25 11.75051413 Original
-20 10 -20 13.18186844
-15 15 -15 14.00859899
-10 20 -10 14.28273586 Optimal
-5 25 -5 14.27044049 Optimal
0 30 0 14.260908 Optimal
5 35 5 12.99996971
10 40 10 11.34923038
15 45 15 9.929587526
Our Design Competing HAWT Competing VAWT
Swept Area (m^2) 0.5044 0.8659 0.6400
Wind Speed (m/s) 12 12 12
Wind Energy (W) 533.86 916.47 677.376
Turbine Power
(W) 118.76 100 108
Turbine Efficiency 22.25% 10.91% 15.94%
Cost $995.00 $1,000.00 $1,000.00
Cost per Watt $8.38 $10.00 $9.26

29
25.40
70
C
D
E
B
F
A
23 14
C
F
E
A
B
D
2 14 3
DRAWN
CHK'D
APPV'D
MFG
Q.A
UNLESSOTHERWISESPECIFIED:
DIMENSIONSAREIN MILLIMETERS
SURFACEFINISH:
TOLERANCES:
LINEAR:
ANGULAR:
FINISH: DEBURRAND
BREAKSHARP
EDGES
NAME SIGNATURE DATE
MATERIAL:
DO NOTSCALEDRAWING REVISION
TITLE:
DWG NO.
SCALE:1:1 SHEET1 OF1
A4
3003 Alloy
WEIGHT: 95.77
Top_Shaft

30
90
25.40
C
D
E
B
F
A
23 14
C
F
E
A
B
D
2 14 3
DRAWN
CHK'D
APPV'D
MFG
Q.A
SURFACEFINISH:
TOLERANCES:
LINEAR:
ANGULAR:
FINISH: DEBURRAND
BREAKSHARP
EDGES
NAME SIGNATURE DATE
MATERIAL:
TITLE:
DWG NO.
A4
3003 Alloy
WEIGHT: 123.13
Bottom_Shaft

31
76240
3.18
C
D
E
B
F
A
23 14
C
F
E
A
B
D
2 14 3
DRAWN
CHK'D
APPV'D
MFG
Q.A
SURFACEFINISH:
TOLERANCES:
LINEAR:
ANGULAR:
FINISH: DEBURRAND
BREAKSHARP
EDGES
NAME SIGNATURE DATE
MATERIAL:
TITLE:
DWG NO.
A4
3003 Alloy
WEIGHT: 3898.60
DOD_S60_disc

32
560.20
25.40
3.18
C
D
E
B
F
A
23 14
C
F
E
A
B
D
2 14 3
DRAWN
CHK'D
APPV'D
MFG
Q.A
SURFACEFINISH:
TOLERANCES:
LINEAR:
ANGULAR:
FINISH: DEBURRAND
BREAKSHARP
EDGES
NAME SIGNATURE DATE
MATERIAL:
TITLE:
DWG NO.
A4
3003 Alloy
WEIGHT: 2108.58
DOD_R90_disc

33
508
50.80
12.70
C
D
E
B
F
A
23 14
C
F
E
A
B
D
2 14 3
DRAWN
CHK'D
APPV'D
MFG
Q.A
SURFACEFINISH:
TOLERANCES:
LINEAR:
ANGULAR:
FINISH: DEBURRAND
BREAKSHARP
EDGES
NAME SIGNATURE DATE
MATERIAL:
TITLE:
DWG NO.
A4
3003 Alloy
WEIGHT: 0.826
Connection Shaft Side

34
14.03
135°
4.70
19.05
7.94
C
D
E
B
F
A
23 14
C
F
E
A
B
D
2 14 3
DRAWN
CHK'D
APPV'D
MFG
Q.A
SURFACEFINISH:
TOLERANCES:
LINEAR:
ANGULAR:
FINISH: DEBURRAND
BREAKSHARP
EDGES
NAME SIGNATURE DATE
MATERIAL:
TITLE:
DWG NO.
A4
3003 Alloy
WEIGHT: 0.826
Connection Shaft

35
K
K
JJ
SECTION K-K
SECTION J-J
C
D
E
B
F
A
23 14
C
F
E
A
B
D
2 14 3
DRAWN
CHK'D
APPV'D
MFG
Q.A
SURFACEFINISH:
TOLERANCES:
LINEAR:
ANGULAR:
FINISH: DEBURRAND
BREAKSHARP
EDGES
NAME SIGNATURE DATE
MATERIAL:
TITLE:
DWG NO.
A4
WEIGHT:
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