Effects of Ground Simulation on the Aerodynamic Coefficients of a Production Car in Yaw Conditions

Paper in proceeding, 2010

Automotive wind tunnel testing is a key element in the development of the aerodynamics of road vehicles. Continuous advancements are made in order to decrease the differences between actual on-road conditions and wind tunnel test properties and the importance of ground simulation with relative motion of the ground and rotating wheels has been the topic of several studies. This work presents a study on the effect of active ground simulation, using moving ground and rotating wheels, on the aerodynamic coefficients on a passenger car in yawed conditions. Most of the published studies on the effects of ground simulation cover only zero yaw conditions and only a few earlier investigations covering ground simulation during yaw were found in the existing literature and all considered simplified models. To further investigate this, a study on a full size sedan type vehicle of production status was performed in the Volvo Aerodynamic Wind Tunnel. The effect of active ground simulation in yawed wind conditions was investigated for different wheel and cooling air inlet configurations. Results show that aerodynamic drag increased more during yaw when using active ground simulation compared to stationary ground conditions. For some of the configurations this resulted in yaw ranges where active ground simulation produced higher aerodynamic drag than with stationary ground. This was mainly connected to the development of the front wheel wakes and the deflection of the windward wheel wake along the underbody during yaw. Aerodynamic lift generally decreased but the front and rear lift balance changed somewhat during yaw for some configurations. Local surface pressure measurements were used to identify important flow field changes and the integrated surface pressures showed a qualitative agreement with the measured drag and lift.