FKFS Veranstaltungen

2025 Stuttgart International Symposium
on Automotive and Engine Technology

3. - 4. Juli 2025

Session: Aerodynamics | | 11:30 - 12:00

Impact of Wheel Drive Unit Secondary Flows on the Aerodynamics of Passenger Cars

Dennis Möllenbeck, Volkswagen AG

State of the art wind tunnels use single belt or five belt systems, the latter consisting of four wheel drive units (WDU) and a large center belt, to simulate the moving ground below the car. Small gaps between the stationary floor and the WDUs are required to measure the forces acting upon them. Through these gaps a pressure induced secondary flow develops between the plenum and the space below, which interacts with the vortex structures around the wheels and tires. Design related leakage from the air bearings of the WDU belt causes additional secondary flows which further differentiate the measuring conditions in the wind tunnel from driving on the street. These effects and their interaction with the flow-field around the car are investigated in this paper. For this purpose, unsteady computational fluid dynamics (3D-CFD) simulations of a full scale DrivAer model and a detailed wind tunnel including a five belt system were conducted. The computations were carried out using the commercial Lattice-Boltzmann software PowerFLOW. Based on these investigations a simplified simulation model was created to simulate different WDU widths. In addition, results of full scale wind tunnel measurements using particle image velocimetry (PIV) will be used as a reference to analyze and review the results from the CFD simulations.