Support Strut Interference Effects on Passenger and Racing Car Wind Tunnel Models 2006-01-0565

In order to provide a correct aerodynamic simulation of a vehicle traveling along the ground, models are tested using rotating wheels in a wind tunnel with a moving ground. In the most common of configurations the model is supported by a vertical strut, usually designed as an aerofoil profile to minimize interference, with the wheels supported by lateral arms hinged to mounts outside the span of the moving ground plane. In using this type of configuration it is assumed that the presence of the intruding supports do not markedly affect the aerodynamic behavior of the model but this assumption is not always valid. In order to quantify interference effects from support struts, several models were tested over a stationary ground plane mounted to an under floor balance. Each model was tested with and without mock struts, which do not actually support the model. Comparisons were made between configurations with and without the mock struts in order to quantify their aerodynamic effects and investigate any changes in flow structure. Force and moment measurements show effects on both drag (up to 23 counts) and lift (up to 170 counts) due to a vertical overhead strut for all vehicle types. The overhead strut wake impinged on the rear wing of racing cars and the backlight of passenger vehicles as expected, but its influence was more wide ranging than this, extending to the vehicle under floor. Racing vehicles, whose performance relies greatly on the vehicles underside flow, are largely affected (up to 250 counts on lift and 26 counts on drag) by the presence of lateral wheel support stings. Passenger vehicles with larger ride heights were not sensitive to the use of lateral supports. Due to the complexity of support interactions, the effect of combined support methods was highly vehicle dependent, precluding the possibility of developing a reliable correction for interference effects.