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1. STUDY OF AERODYNAMIC EFFECT OF SPOILER ON
A CAR
A N S Y S P R O D U C T S 1 4 . 5
Bhola Patel
Design Engineer at CADmantra Technologies Pvt. Ltd.

2. INTRODUCTION
Nowadays everyday cars are changed by their owners to make the look sportier.
Aerodynamic properties of the car given by the designer are not enough to offer the required down
force and handling at high speeds.
Extra parts are added to offer greater drag reduction to the car and at the same time enhance the
stability.
Our focus is on the rear spoiler.

3. PROBLEM STATEMENT
• When a driver drives his or her car in high speed condition(>110
km/hr)
• high tendency to lift over
• once the air makes its way to rear window, the notch created by the
window dropping down to the trunk leaves a vacuum or lower pressure
space that the air is not able to fill properly.
• and the resulting lower pressure creates lift that then acts upon the
surface area of the trunk
• To reduce lift that acted on the rear trunk, a rear spoiler can attach on
it to create more high pressure

4. PROJECT OBJECTIVE
investigate the effects of aftermarket rear spoiler to the car aerodynamic drag and lift.
by estimate the value of CD and CL
The differences between car with and without spoiler can be determined
Tow models of rear spoilers will be chosen and the 3-D models will be built in CAD software
according the actual dimension.
analyzed in CFD software to estimate the value of CD and CL
which rear spoiler either reduce drag or reduce lift force, or reduce both or not can be determine

5. PROJECT DESCRIPTION
An investigation on effects of rear spoiler to car aerodynamic drag and its stability will be done by
estimate the value of CD by doing some CFD analysis
several designs will be selected to build up model in CAD software
The models will built up according its actual dimension to make sure any errors during analyzing can be
avoided
models then will be analyzed in CFD to estimate value of drag force and lift force
From the value of both forces, the value of CD and CL can be estimate and the data then interpret into
graph or scatter plot and also into bar chart

6. GENERAL AERODYNAMICS CONCEPTS
Bernoulli’s Equation :
p + ½ ρ v2 + γ z = constant along streamline
Fig - Pressure and velocity gradient in the air flow over

7. DRAG AND LIFT CONCEPT
1 . S H E A R S T R E S S W H I C H A C T P A R A L L E L T O T H E B O D Y S U R F A C E
A N D C O N T R I B U T E S O N L Y T O D R A G .
2 . P R E S S U R E W H I C H A C T S N O R M A L T O T H E S U R F A C E I S
R E S P O N S I B L E F O R A V E H I C L E ’ S L I F T A N D P A R T O F D R A G .

8. dFx = ( p dA) cos θ + ( τw dA) sin θ
dFy = - ( p dA) sin θ + ( τw dA) cos θ
AERODYNAMICS FORCES
DA = ½ ρ v2 CD A
Where CD = coefficient drag [dimensionless]
A = frontal area [m2]
ρ = density of air [kg/m3]
v = velocity of vehicle [m/s]
Drag Force

9. Lift force
LA = ½ ρ v2 CL A
LA = lift force
CL = coefficient of lift
A = frontal area
Downforce
Downforce is created
when air moves
through and over parts
of the car.

10. MODELING
The models will build up in CAD software
SolidWorks will be use to build up the model
the model will be design according the actual dimension to make sure it can produce an
approximately accurate
it also must fix with the base line model that will be use
Airfoil spoilers are used.

11. BASE LINE MODEL

13. REAR SPOILER MODEL
2 different spoiler styles have been used.
“wing” style spoiler, which was mounted 23 cm above the
on the other hand the second spoiler was mounted edge of the rear side of the vehicle without leaving a
gap between spoiler and the surface of vehicle

15. The models of both vehicle and two different spoilers have been made using the software called
SolidWorks to CAD format for numerical .

18. VIRTUAL WIND TUNNEL
Around the 3d cad model a virtual wind tunnel is
made with the help of inventor.
The complete domain was divided to half using a
symmetry plane (YZ plane).

21. CFD SOLVER BOUNDARY CONDITION
Boundary Conditions (for all cases and benchmarks)
Velocity Inlet Magnitude and Direction 30m/s (Positive Z-direction)
Turbulence Intensity 1.00%
Pressure
Outlet
Gauge Pressure magnitude 0 Pascal
Gauge Pressure direction Normal to boundary
Turbulence Specification Method Intensity and Viscosity Ratio
Backflow Turbulence Intensity 10%
Wall Zones No Slip
Symmetry No Slip
Fluid
Properties
Fluid Type Air
Density 𝜌 = 1.2 kg/m3

22. CFD SIMULATION
The following cases which have to be simulated:
Case #1: Vehicle model without rear-spoiler.
Case #2: Vehicle model with the first rear-spoiler design.
Case #3: Vehicle model with the second rear-spoiler design.

23. Velocity distribution of flow for case #1
Velocity distribution of flow for case #2
Velocity distribution of flow in the symmetry plane for case #3

24. As we see in the there were two different
recirculation zones .
There is only one recirculation zone.

25. CD GRAPHS
There was significant change in terms of drag
force when comparing case #1 and case #2.
Case #3 was not considered.

26. CL GRAPHS

27. RESULT
Velocity
(km/h)
Drag Force (N) Lift Force (N) CD CL
70 241.41 -224.69 0.232 -0.2160
80 294.75 -274.42 0.233 -0.2170
90 353.50 -329.12 0.234 -0.2182
BLM car without Rear Spoiler
Velocity
(km/h)
Drag Force (N) Lift Force (N) CD CL
70 199.72 -276.69 0.1920 -0.2660
80 243.92 -337094 0.1931 -0.2675
90 292.55 -405.31 0.1945 -0.2680
BLM car with Spoiler #1
Velocity
(km/h)
Drag Force (N) Lift Force (N) CD CL
70 225.73 -382.8 0.2170 -0.368
80 275.69 -467.53 0.2182 -0.3695
90 330.64 -560.73 0.2193 -0.370
BLM car with Spoiler #2

28. CONCLUSION
The spoiler used in case #2 exhibited a significant reduction in drag force and in small increase
negative lift force.
The spoiler used in case #3 displayed a relatively smaller reduction in drag force but a huge increase
in negative lift force.
If safety is major concern , then handling of car would much superior of spoiler in case# 3 and would
be selected for the design of the car.

29. FUTURE SCOPE
Companies such as Porsche, Bugatti or Mercedes have been using different technologies for
spoilers.
A type of such technology is the hydraulic spoiler.
This is currently being used in Bugati Veyron.

30. REFERENCES
Carr G.W. The Study of Road Vehicle Aerodynamics, Using Wind Tunnel Models. Paper 14, Proc. 1st Symp. Road Vehicle Aerodynamics, London,
1969.
Website:* http://www.nasa.gov/audience/forstudents/5-8/features/what-is- aerodynamics-58.html.
Website: http://www.grc.nasa.gov/WWW/K-12/airplane/boundlay.html.
Website : http://en.wikipedia.org/wiki/Bernoulli's_principle
Website : http://www.slideshare.net/pparmaei/aerodynamic-carsscience
Website : http://www.slideshare.net/sharadadevi79/pr-2-33068013
Website : http://help.autodesk.com/view/SCDSE/2014/ENU/?guid=GUID-94E433C2-1580-4575-A6FA-2E7F22A23EB6
Website : http://help.autodesk.com/view/SCDSE/2014/ENU/?guid=GUID-3AF255C7-4F5B-4DCB-825A-726698D50510
Website : http://help.autodesk.com/view/SCDSE/2014/ENU/?guid=GUID-BC3E47DC-6626-41C6-974F-4D5676FAE066