Aerodynamics study on spoiler of car

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1. Study Of Aerodynamic Effect Of Spoiler On A Car ANsYS PRODUCTS 14.5 Bhola Patel Design Engineer at CADmantra Technologies Pvt. Ltd.

2. INTRODUCTION Nowadays everyday cars are changed by their owners to make the look sportier. A erodynamic 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. Shear stress which act parallel to the body surface and contributes only to drag. 2. Pressure which acts normal to the surface is responsible for a vehicle’s lift and part of drag.

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 T he 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

12. 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

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

14. 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 ).

15. 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/m 3

16. 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.  

17. 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

18. As we see in the there were two different recirculation zones . There is only one recirculation zone. Figure 3.16 Velocity streamlines of flow in the symmetry plane for case #2 As we see in the Figure 5.8 there were two different recirculation zones at the rear end of the vehicle (one behind the vehicle, and one above the rear window). By comparing Figure 5.8 and Figure 5.9 it has been seen that; the recirculation zone above the rear window was almost gone by using spoiler. The air slopes gently above the rear window, which helps keeping the rear window cleaner. It has been found that keeping the rear window cleaner is one of the advantages of using spoiler.

19. Cd graphs There was significant change in terms of drag force when comparing case #1 and case #2. Case #3 was not considered.

20. Cl graphs and case #3.

21. RESULT V e l o c i t y ( k m / h) D r a g F o rc e ( N) L i f t F o r c e ( N ) C D C L 7 241.41 -224.69 .232 -0.2160 80 294.75 -274.42 . 233 -0.2170 90 353.50 -329.12 . 234 -0.2182 BLM car without Rear Spoiler V e l o c i t y ( k m / h) D r a g F o rc e ( N) L i f t F o r c e ( N ) C D C L 7 199.72 -276.69 0.1920 -0.2660 80 243.92 -337094 . 1931 -0.2675 90 292.55 -405.31 . 1945 -0.2680 BLM car with Spoiler #1 V e l o c i t y ( k m / h) D r a g F o rc e ( N) L i f t F o r c e ( N ) C D C L 7 225.73 -382.8 .2170 -0.368 80 275.69 -467.53 . 2182 -0.3695 90 330.64 -560.73 . 2193 -0.370 BLM car with Spoiler #2

22. 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.

23. 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.

24. 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