Wheel Aerodynamic Developments on Passenger Cars by Module-based Prototype Rims and Stationary Rim Shields

Paper in proceeding, 2010

Wheel and underbody aerodynamics become increasingly important as the demand on road vehicles increases. With limitations in allowable CO2 emissions, reducing fuel consumption on passenger cars is essential in order to stay competitive. One important feature of wheel aerodynamics is the rim design which has been investigated in detail in this study. In order to explore wheel aerodynamics, a module-based prototype rim system was designed and implemented on full scale passenger cars. The module based system consists of a slimmed down basic aluminum rim with add-on modules manufactured by SLS rapid prototyping. Stationary rim shields similar to what are used in Grand Prix racing was also studied in the research. Comprehensive investigations were performed in the Volvo Aerodynamic Wind Tunnel on a Volvo V70 and S80 respectively. Global force measurements were performed on all configurations along with base pressure measurements. A probe rake with two Omniprobes was used for local flow field investigations around the front right wheel. Results show that rim parameters such as location and size of rim openings have large influence on the aerodynamic performance of passenger cars. Good indications of important areas of the rim to cover for low drag were achieved. Stationary rim shields showed good potential in further reducing drag for passenger cars. Opening positions and shield gaps towards the rotating rims were found to have noticeable influence on aerodynamics. The local flow field investigation showed that the front wheel wake structures were significantly affected by different rim designs. A qualitative agreement between reduced ground wake and lower overall aerodynamic drag was observed. Additional possible mechanisms for aerodynamic drag reduction due to rim design and stationary rim shields are discussed.