Propulsion efficiency improvement through CFD

1. Propulsion efficiency improvement through
CFD
Vessel Efficiency
Simon Lewis
Tuesday 27th November2012

2. Overview of presentation
CJR Propulsion and initial propeller design tools
Analysis of a hull using CFD
Optimisation of propeller design
P-bracket analysis and design using CFD – A case study
Spray analysis
Rudder design
Recent successes
Future work

3. CJR Propulsion Ltd. – Company background
CJR propulsion is a leading propeller design and manufacture company
Also manufacture other underwater hull appendages such as rudders, P-brackets
and propeller shafts.
World leader in advanced manufacturing methods – One of the only companies
in Europe with the capability to machine propellers with a 5-axis CNC milling
machine

4. Initial Propeller performance calculations
Historically, propeller design was based on propeller series data and experience
A lifting surface model and ship resistance prediction program was introduced to
the design procedure in 2007. This allows:
• Accurate hull resistance prediction
• Accurate propeller performance prediction
• Cavitation on the propeller blades to be predicted (subject to accurate
inflow data)
• Pressure field around the hull as well as pressure pulses on the hull are
calculated – these are responsible for propeller noise and vibration
(subject to accurate inflow data)

5. Limitations of this method
No method for determining the realistic inflow to the propeller plane – a uniform
flow is assumed, although this is not the case as the flow has to travel
passed the shaft and shaft bracket before reaching the propeller.
Cavitation and propeller pulses cannot be accurately predicted if the inflow
conditions are not known.
In order to improve the rudder design, the flow entering the rudder region must
be known.
No method of determining the effect of the shaft, shaft bracket and other
appendages on the propeller performance

6. Knowledge transfer partnership
In order to overcome these limitations, CJR decided to seek assistance from the
University of Southampton.
The two organisations won funding for a 2 year knowledge transfer partnership
(KTP) funded by the TSB
The aim of the KTP was to improve sterngear design through the use of advanced
computational fluid dynamics (CFD).

7. CFD analysis of a planing hull
CFD mesh of the hull and
appendages.
Free surface showing
hull wake.

8. Analysing the flow into the propeller
CFD mesh of the hull and appendages.

9. CFD analysis of a planing hull
Streamlines of the flow
under the hull
Cross flow velocities
in the propeller plane

10. CFD Study - Results

11. Case Study: P-bracket design
The aim is to demonstrate how the P-bracket design alters the flow into the
propeller. This is achieved by
• Simulating the flow around a hull using CFD to gain a better
understanding of the flow into the propeller.
• Altering the P-bracket design and analysing the effects:
-8º 15º 26º

12. Preliminary CFD Study – Propeller plane
Velocity in the x direction (forward velocity)
26º P-bracket
-8º
15º

13. Propeller Design
Four propellers are analysed once the wake predictions are completed
Propellers are analysed in the following flow regimes:
• Uniform wake
• CFD predicted wake with -8º P-bracket
• Trials data with -8º P-bracket
• CFD predicted wake with 15º P-bracket
• CFD predicted wake with 26º P-bracket
Propellers are analysed using in-house code and a vortex lattice method

14. Propeller Design – Thrust predictions

15. Propeller Design – Torque predictions
15 5x42.5x49
5x42.5x50.5
14.5
5x42.5x50.5 MOD
14
5x42.5x50.5 REV
Torque (kNm)
13.5
13
12.5
5x42.5x50.5 REV
12
5x42.5x50.5 MOD
11.5
5x42.5x50.5
Uniform
-8 5x42.5x49
-8 trials
15
26

16. Propeller Design –prediction of pressure pulses on hull
30 5x42.5x49
25 5x42.5x50.5
Pressure pulses (kPa)
20
5x42.5x50.5 MOD
15
5x42.5x50.5 REV
10
5x42.5x50.5 REV
5
5x42.5x50.5 MOD
0
5x42.5x50.5
Uniform
-8
5x42.5x49
-8 trials
15
26

17. Propeller Design –prediction of cavitation
Cavitation erosion

18. Case study conclusions
A design procedure for improving stern gear has been presented
The initial results suggest that there are significant savings to be made in
terms of stern gear drag and propeller noise and vibration.
P-bracket design affects the propeller performance and optimisation of this
component provides
• A cleaner flow into the propeller.
• Significant reduction in the predicted pressure pulses on the hull.
• Increase in propeller thrust and torque.
Cavitation predictions are comparable with reality when the CFD wake is used

19. Trim and resistance analysis
Variation of drag with displacement for
three different trim angles.
• Prediction of drag and running trim.
• Calculation of optimum position of the centre of gravity.
• Sensitivity studies can be undertaken to evaluate the effect of changing the hull
parameters including displacement.

20. Propeller race
CFD simulation of the propeller and entire hull
Axial velocity
Vertical velocity

21. Rudder design
Two rudder designs are analysed
Rudder A is a wedge rudder with a blended stock, and toed in by 2.5 °
Rudder B is a wedge rudder without a blended stock and has no toe in angle

22. Rudder design
Pressure on rudder surfaces at 0 degrees pitch.
Rudders at 35 degrees pitch, with streamlines.

23. CFD Spray analysis
CFD mesh of the hull is refined at the free surface.

24. CFD Spray analysis
Analysis of the free surface flow.
• Evaluate the spray of a planing craft in calm water.
• Effect of changes in the hull design (such as spray rail dimensions) on the spray.

25. Recent success stories
The propeller design of the following yachts has used all or some of the
method presented:
Manufacturer Yacht Required speed (kts) Achieved
speed (kts)
Alnmaritec 16m Pilot boat 25 27.6
Alnmaritec 19m patrol boat 36 37.6
Holyhead Marine 16m Pilot boat 25 28
Mustang Marine Humber pilot boat 25.7 (previous props) >27
Seaward Marine Tenerife pilot boat 21 23.5
Seaward Marine Guernsey ambulance boat 25 26.7

26. Conclusions
The collaborative research and development project has been a huge
benefit to both the University of Southampton and CJR Propulsion:
CJR made extensive use of the resources at the university such as the
Iridis 3 computer cluster and the in house CFD expertise gained from
years of research.
The university has improved links to industry, and gained insight and
knowledge from the research carried out during the project.
The improved lines of communication between the two has allowed
further collaboration in the area of composite propellers which included a
student at the university working on a summer placement at CJR.
CJR now offer a CFD consultancy service

27. CFD consultancy work by CJR

28. CFD consultancy work by CJR
Picture courtesy of ICAP leopard

29. Future work
Improve the propeller momentum source in the CFD to include variations
in the propeller thrust and torque as each blade sweeps around the disk
Further sea trials are planned with a variable rudder toe in angle in order
to fully quantify the effect of this against speed and turning performance
Including hull motion in the CFD to allow the hull to find its own heave
and trim, and eliminate the need to carry out a matrix of nine simulations
Include the full propeller model in the CFD simulation to further enhance
predictions.

30. Future work

31. Questions
?
Simon Lewis
Simon@cjrprop.com
07868742997