I have uploaded this to use as a guide, the numbers have not been peer-reviewed.

1. ASSIGNMENT 4
OPTIMISATION OF A WING IN GROUND CLEARANCE
MIET 2004 Mechanical Design
Hashan Mendis s3449757

2. EXECUTIVE SUMMARY
In order to maximise downforce created by the front wing, the optimum ground clearance and flap angle of
the rear element was determined.
As ANSYS has optimisation function built into the program, it was deemed unnecessary to spend resources on
understand the code. Instead Matlab was utilised to graph the data produced.
Using ANSYS CFX which is a Computational Fluid Dynamics (CFD) program, simulations in 2D were performed.
The geometry contained the profiles within the domain. A domain independence study was performed to
ensure the domain didn’t affect the results. It resulted in an inlet and wall 5 m away from the profile, and
outlet 10 m behind. After the geometry was meshed a mesh study was also performed to ensure mesh
independence, resulting in a 300 mm volume mesh of the outer domain, 50 mm volume mesh of the inner
domain, 1 mm edge sizing around the wing and an inflation layer with the first element being 0.02 mm from
the surface of the wing.
Each simulation took 1 minute and focused on changing the ground clearance and flap angle to create a full
design of experiments. The results showed maximum coefficient of lift (Cl) at 20° flap angle at 110 mm ground
clearance.
A partial design of experiments in 3D performed showing a maximum Cl of 1.42, with a 30° flap and 70 mm
ground clearance. The different between the results is due to the different pressure distribution. The even
pressure distribution present in the 2D results changes in 3D due to vortices and different pressure regions
interacting.
The design was then optimised by adding plates on the end plates and strakes under the wing. This controlled
the air flow and hence pressure distribution. It resulted in a 30% increase of Cl from 1.42 to 1.85.
Problems faced in the simulation revolved around obtaining solution that converged. The mesh had to be
refined in 3D as the geometry complexity increase. Vortices were being created that required a finer mesh.
Run times in 3D taking hours, required an understanding of how to interpreting the CFD data, ensuring
appropriate modification were performed that would return an expected result.
KEYWORDS
Front Wing, aerodynamics, FSAE, CFD, ANSYS, CFX, wing, profile, ground clearance, optimisation,

3. Contents
EXECUTIVE SUMMARY......................................................................................................................................... 2
KEYWORDS .......................................................................................................................................................... 2
INTRODUCTION ................................................................................................................................................... 4
METHODOLOGY............................................................................................................................................... 4
CFD....................................................................................................................................................................... 5
GEOMETRY ...................................................................................................................................................... 5
MESH ............................................................................................................................................................... 5
SET UP.............................................................................................................................................................. 5
SOLUTION........................................................................................................................................................ 6
DESIGN OF EXPERIMENT ................................................................................................................................. 6
OPTIMIZATION..................................................................................................................................................... 6
Conclusion ........................................................................................................................................................... 7
Appendix A – Residuals and Monitor Points ....................................................................................................... 8
Appendix B – DOE Results ................................................................................................................................. 10
Appendix C – Pressure Distribtion of 2d and 3d flow........................................................................................ 11
Appendix D - flow structure - 30° flap angle, 70 mm ground clearance........................................................... 12
Appendix E – Long end plate............................................................................................................................. 13
Appendix F – foot and side plate....................................................................................................................... 14
Appendix H – cut away end plate and Top Plate............................................................................................... 16
Appendix I – strakes on wing............................................................................................................................. 17
Appendix I – variations of the designs............................................................................................................... 18
Table of Figures
Figure 1 - Front Wing Design – Double element profile, end plate and mounting plate.................................... 4
Figure 2- Simplified model of the FSAE car ......................................................................................................... 4
Figure 3- 3D geometry used ................................................................................................................................ 5
Figure 4-2D Geometry used for CFD.................................................................................................................... 5
Figure 5-Volume sizing of the domain in 2D ....................................................................................................... 5
Figure 6- Inflation layer around wing .................................................................................................................. 5
Figure 7- Modified front wing design with plates and strakes............................................................................ 7

4. INTRODUCTION
The aerodynamics package of the FSAE car as shown in Figure 1 consisting of a front and rear wing used to
increase the average cornering speed of the race car.
The current design of the front wing in Figure 2. As the middle section of the wing is fixed, the section with
two elements will be analysed will be optimised to increase the Cl using ANSYS CFX which is a CFD simulator.
ANSYS CFX is a CFD simulation software that predicts air flow and force. The coefficient of lift is a dimensionless
number and in this case indicated how much downforce can be created.
The pressure distribution between the top and bottom surface of the wing is essential to creating downforce.
As ground clearance of the wing decreases, a venturi is created, cross sectional area decreases, flow
accelerates, pressure underneath the wing drop, increasing the pressure difference which creates more
downforce. The pressure drop increases the adverse pressure gradient and flow will separate if it is too large,
reducing downforce. Flow separation is sensitive to the flap angle with large flap angle generating a large
pressure gradient.
In order to increase downforce, the ground clearance and flap angle needs to be evaluated and then the design
optimised.
METHODOLOGY
The flow fields of the front wing are effect by the car but running a full car simulation will increase
computational time. To reduce complexity a front wing in isolation will be studied, with a varying second flap.
2D and 3D simulations can be run in CFD. 2D simulations have a quick run time however doesn’t take into
account vorticity and different pressure regions interacting. The coefficients are overstated but using a
constant set up general trends can be deduced.
3D simulations can take hours to solve but accurately predict flow fields of complex 3D geometry.
Due to the quick run time 2D CFD will be utilised to perform a full design of experiments. The ground clearance
will vary from 50mm (minimum wing height due to pitch and roll) in 20mm increments and flap angles ranging
from 10° to 40° in 10° increments. Matlab will be used to plot data.
A partial design of experiments will be conducted in 3D focusing on areas that yield high Cl.
Figure 1 - Front Wing Design – double element profile, end plate and
mounting plate
Figure 2- Simplified model of the FSAE car

5. After an optimum ground clearance and flap angle have been established the design will be optimised to
increase Cl.
CFD
GEOMETRY
The double element profile in the domains have the ability to translate and rotate the rear flap angle. The 2D
geometry took a 1 mm slice of the profiles where the 3D geometry has a 400 mm span as shown in Figure 3.
with fixed end plate. Due to geometry symmetry a half model was simulated, reducing computational time.
A domain study was conducted in order in order to ensure the walls do not affect the results and the outlet is
far enough to resolve the wake. The inlet and top wall placed 5000 m away from the profile and outlet 10000
mm behind as shown in Figure 4. In 2D the wall has a 1 mm width, 3D a 4000 mm width. The inner domain
allows a fine mesh to be created locally around the wing capture important flow fields.
MESH
A mesh study was conducted to establish independence. It consists of tetrahedron elements that are able to
contour to the complex geometry. The outer domain has a volume sizing of 300 mm, inner domain of 50 mm
and 1 mm edge sizing around the wing as shown in Figure 5. Prism elements on the surface of the wing are
used to capture the boundary layer, consisting of 20 elements with the first element height set to 0.02 mm as
shown in Figure 6 resulting in a total element count of 43 000 in 2D and 11 000 000 in 3D. As the complexity
of the 3D geometry increase, a 20 mm inner volume mesh was required to solve.
SET UP
The inlet and ground speed was set to 60km/hr which is the average car speed. The wing has a no slip condition
allowing a boundary layer to be formed. The walls have a free slip condition; this bounds flow but won’t affect
pressure. The turbulence model used is called Shear Stress Transpose as it can resolve a fine boundary layer
accurately which is important to predict separation. Convergence criteria was set to 1e-6 with downforce
monitors to ensure stability.
Figure 6- Inflation layer around wing
Figure 3- 3D geometry used Figure 4-2D Geometry used for CFD
Figure 5-Volume sizing of the domain in 2D

6. SOLUTION
The monitor points which measured downforce of the wing are constant with the residuals declining indicating
a converged simulation. A sample if produced in Appendix A for a 2D run. If issues occurred the mesh was
altered. A typical simulation took 1 minute in 2D and 2 hours in 3D.
DESIGN OF EXPERIMENT
The data from the experiments were added to an excel file. Matlab was then used to read the data and plot it
as seen in Appendix B
The 2D full design of experiments show the trends are unimodal for each flap angle. The maximum Cl is
between a ground clearance of 90 mm to 110 mm. Flow starts to separate at 30° flap angles which is why 20°
has the highest Cl.
The difference between the maximum Cl and neighbouring data points is under 5% which is deemed
acceptable. 5% difference of Cl results in a 1kg difference at 60km/hr which won’t affect performance.
The 3D partial design of experiments started at 110 mm ground clearance at 20° flap angle. Ground clearance
adjusted until Cl peaked. The results showed 20° flap angles reached a maximum Cl of 1.35 and 30° max Cl of
1.42 at 70 mm ground clearance. At 40° the flow separates at high ground clearance, decreases ground
clearance would increase the pressure gradient exasperating separation. To save computational time the 40°
angles were neglected. The difference between the neighbouring data points is under 5% showing that there
isn’t a noticeable difference between the flap angles or ground clearance.
The reason the 2D design of experiments under predicted separation angle and ground clearance is due to the
pressure distribution between 2D and 3D flow.
The pressure contour of a 2D simulation is 200 Pa lower mid chord than the 3D simulations as seen in Appendix
C. The pressure difference is due to the different flow conditions. In 2D, the flow is chord wise resulting in an
even pressure distribution. In 3D, due vortices and different pressure gradients interacting, the air flow travels
chord and span wise. The change in flow, changes the pressure distribution, resulting in higher pressure
underneath the wing. This results in a lower pressure gradient, allowing the wing to push higher angles, and
lower ground clearances.
This shows that the 2D simulations need to be tested in 3D but can be used to understand how variables
interact and where to start.
OPTIMIZATION
Appendix D shows the flow structure of the wing at 30° flap angle at 70 mm ground clearance. Due to the
pressure difference between the wing and free stream air, a clockwise vortex on the bottom edge of the end
plate and anticlockwise vortex on the top edge is formed. As discussed, the vortex interferes with the pressure
distribution reducing efficiency. The first iteration was to extend the end plate till it was 40 mm above the
ground as shown in Appendix E. This ensured in pitch and roll the wing didn’t bottom out. The long end plate
moved the vortex away from the bottom surface of the wing, lowering the pressure, increasing Cl by 8%.
A 19 mm foot and side plates were added to the end plate as seen in Appendix F. It lessens the intensity of the
vortex on the bottom side and moves the top vortex away from the wing. It reduced its effect on the pressure
distribution of the wing which increased Cl by 9%.
A C-channel section was also tried to produce the same effect as seen in Appendix G. The idea was that the
channel would contain the vortex. On comparison the Cl was the same, as the foot plate would be easier to
manufacture it was chosen.

7. A section of the top end plate was taken out match the profile of the mounting plate. Top plates were then
added, pushing the top vortex away from the wing as seen in Appendix H. The design increased Cl by 2%.
In order to control the vortex created on the lower side strakes were added as seen in Appendix I. The strakes
would control the air flow and contain the vortex. 3 strakes were added at 20mm apart, any more saw no
return. The pressure distribution of the lower surface with the strakes show a larger low pressure region
contained by the strakes, with the vortex having a smaller effect. The design saw a 9% increase in Cl.
The double element section of the design has changed from the simple design to add plates along the end
plate and strakes underneath the wing.
Overall the design saw an increase of 30% downforce with a Cl of 1.85. Appendix J has a list of design changes
with respective Cl. If time was available, the next steps would be to add the wing to the car with rotating
wheels to understand how the flow fields change.
CONCLUSION
The front wing is a vital component of the aerodynamics package in creating downforce. An analysis needed
to be conducted to understand what the optimum ground clearance was at different flap angles and if the
design could be optimised.
A full design of experiments was conducted in 2D at ground clearances varying from 40 mm to 150 mm at flap
angles ranging from 10° to 40°. The results showed a unimodal trend, the maximum Cl produced 20° at 90 mm
ground clearance with flow separation at 30°.
The partial design of experiments in 3D showed max Cl at 30°, 70 mm ground clearance. The difference in data
from the 2D is due to the change of the pressure distribution along the surface of the wing.
The design was then optimised to increase Cl, increasing 30% from 1.42 to 1.85 due to the addition of plates
on the end plate and strakes on the wing. The devices controlled air flow by controlling the vortices created.
If time was available, the next steps would include adding the wing to the chassis with rotating tires to
understand the flow fields and how they change.
Figure 7- Modified front wing design with plates and strakes

8. APPENDIX A – RESIDUALS AND MONITOR POINTS
RESIDUALS OF A 2D SIMULATION

9. MONITOR POINTS OF A SIMULATION STABILISING

10. APPENDIX B – DOE RESULTS
DOE RESULTS

11. APPENDIX C – PRESSURE DISTRIBTION OF 2D AND 3D FLOW
2D PRESSURE DISTRIBUTION
3D PRESSURE DISTRIBUTION

12. APPENDIX D - FLOW STRUCTURE - 30° FLAP ANGLE, 70 MM GROUND CLEARANCE
PRESSURE DISTRIBUTION OF THE END PLATE
PRESSURE DISTRIBUTION OF THE END PLATE WITH VORTEX REGION CORES HIGHLIGHTED IN GREY.
PRESSURE DISTRIBUTION OF THE BOTTOM SURFACE OF THE WING

13. APPENDIX E – LONG END PLATE
PRESSURE DISTRIBUTION WITH LONG END PLATE
PRESSURE DISTRIBUTION WITH LONG END PLATE HIGHLIGHTING VORTEX REGION
PRESSURE DISTRIBUTION OF THE BOTTOM SURFACE OF THE WING WITH LONG END PLATE

14. APPENDIX F – FOOT AND SIDE PLATE
FOOT PLATE AND SIDE PLATE ADDED
VORTEX GENERATED FROM FOOT PLATE HAS LESS INTENSITY, TOP VORTEX IS PUSHED AWAY FROM THE WING
PRESSURE DISTRIBUTION OF THE BOTTOM SURFACE OF THE WING WITH FOOT AND SIDE PLATES.

15. APPENDIX G – C-CHANNEL DESIGN
C CHANNEL ON END PLATE

16. APPENDIX H – CUT AWAY END PLATE AND TOP PLATE
TOP PLATES CREATE A VORTEX AWAY FROM THE WING
PREVIOUS DESIGN WITH A VORTEX OVER THE WING

17. APPENDIX I – STRAKES ON WING
DESIGN OF THE STRAKES
PRESSURE DISTRIBUTION UNDERNEATH THE
WING
VORTEX CREATED FROM BOTTOM
SURFACE
VIEW OF THE VORTEX FROM THE FRONT
PLANE

18. APPENDIX I – VARIATIONS OF THE DESIGNS
VARIATION CL
70MMGROUND CLEARANCE 1.42
LONG END PLATE 1.53
LONG END PLATE AND FOOT PLATE 1.67
LONG END PLATE, FOOT PLATE AND TOP PLATE 1.70
LONG END PLATE, FOOT PLATE, TOP PLATE AND STRAKES 1.85
TABLE OF VARIOUS DESIGNs