Detailed Flow Studies in Close Proximity of Rotating Wheels on a Passenger Car

Moving ground systems with rotating wheels have been used in wind tunnel tests during the last decades. Several studies on the effects of rotating wheels and the importance of wheel aerodynamics have been published. It is well known that both the local flow field and the global aerodynamic forces are affected by rotation of the wheels. Different studies indicate that the most significant effect from rotating the wheels is interference effects between the rear wheels and the underbody and vehicle base [1], [2].

A detailed flow field investigation around the wheels in close proximity to the vehicle has been performed on a passenger car in the Volvo Aerodynamic Wind Tunnel. Two omnidirectional 12-hole pressure probes were traversed in a number of planes close to the wheels. Effects of changing different parameters such as ground simulation and rim geometry were investigated. The local flow field has been scrutinised and related to the global aerodynamic properties of the vehicle.

A clear dependency on ground simulation as well as a dependency on wheel geometry was found in the local flow field. All configurations showed lower global drag with moving ground activated. Generally a good correlation with numerical results was observed.