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.

INTRODUCTIONNowadays 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.

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

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 CLwhich rear spoiler either reduce drag or reduce lift force, or reduce both or not can be

determine

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 forceFrom 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

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

DRAG AND LIFT CONCEPT1 . 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 LY 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 .

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

Lift forceLA = ½ ρ v2 CL A LA = lift force CL = coefficient of lift A = frontal area

DownforceDownforce is created when air moves through and over parts of the car.

MODELINGThe models will build up in CAD softwareSolidWorks will be use to build up the modelthe model will be design according the actual dimension to make sure it can

produce an approximately accurateit also must fix with the base line model that will be useAirfoil spoilers are used.

BASE LINE MODEL

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

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

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).

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 PascalGauge Pressure direction Normal to boundaryTurbulence Specification Method

Intensity and Viscosity Ratio

Backflow Turbulence Intensity 10%Wall Zones No SlipSymmetry No SlipFluid

 Properties

Fluid Type AirDensity 𝜌 = 1.2 kg/m3

CFD SIMULATIONThe 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. 

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

As we see in the there were two different recirculation zones .

There is only one recirculation zone.

CD GRAPHS

There was significant change in terms of drag force when comparing case #1 and case #2.

Case #3 was not considered.

CL GRAPHS

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

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.

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.

REFERENCESCarr 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_principleWebsite : http://www.slideshare.net/pparmaei/aerodynamic-carsscienceWebsite : http://www.slideshare.net/sharadadevi79/pr-2-33068013Website :

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