What difference will adding a rear wing to a car make? You can expect an increase in downforce, equivalent to a reduction in lift, and an increase in drag. To quantify these effects I simulated the aerodynamics of a BMW Z3 using Computational Fluid Dynamics (CFD) without a wing and with a wing.

CFD Simulation of a Car with a Rear WingVelocity contours and streamline arrows

Background

The primary role of a rear wing mounted on a car is to increase downforce. With more downforce you can corner faster by effectively increasing the weight of the car and thus putting a higher load on the tires to prevent them from sliding. Usually extra downforce is accompanied by an increase in drag. Increased drag means slower straight line speed. However, on balance sacrificing some straight line speed for faster cornering turns out to be a race-winning strategy as in Formula 1.

CFD Models

The original half car (symmetrical) geometry was imported as a STEP (.stp) file, cleaned up, and integrated into a larger bounding flow volume to form the model for the wingless car CFD simulation.

CFD Car Geometry

The original flow volume was then modified by adding the rear wing to produce a second model for this comparison study.

CFD Car Geometry with a Wing

Results

CFD Simulation of a Car without a WingFront view of velocity contours and streamline arrows

CFD Simulation of a Car without a WingRear view of velocity contours and streamline arrows

CFD Simulation of a Car with a WingFront view of velocity contours and streamline arrows

CFD Simulation of a Car with a WingRear view of velocity contours and streamline arrows

CFD Lift and Drag Comparison for a Car with and without a Wing

The wing produces a dramatic increase in the downforce, equivalent to a reduction in lift, for only a relatively small increase in drag.

Conclusion

This CFD studies shows that adding a rear wing to the car dramatically increases the downforce with only a relatively small increase in drag. The addition of the rear wing is likely to positively affect the performance of the car in a race. However, for more optimally balanced handling a front aerodynamic device, e.g., a splitter, would be another addition to consider.

You may have noticed that this wing is idealized in that I have not modeled the mounting brackets - stay tuned for more on wing mounting options.

Notes

• Original car geometry courtesy of Andrew Shedden, as pro engineering
• Car speed equivalent to 65 mph, with moving ground and rotating wheels
• Simulations set up and performed in Caedium Professional using the incompressible, steady-state RANS solver, and the k-omega SST turbulence model