Effect of moving ground on the aerodynamics of a generic automotive model: The DrivAer-Estate

Abstract With the recent trend to require automotive aerodynamic testing in wind tunnels with rolling-road floors, this study investigates the impacts of the ground configuration on the aerodynamic characteristics of a generic estate-type vehicle – the DrivAer-Estate. This is based on a comparison between time-dependent computational predictions for two configurations: one with a stationary ground with stationary wheels, and another with a moving ground and rotating wheels. This study quantifies the time-averaged flow structures, wake dynamics, surface pressure distributions and aerodynamic loadings, and by comparing these for the two cases. This study determines the distinct flow features and the mechanism of how different ground simulations affect the aerodynamic characteristics. Predictions using an Improved Delayed Detached Eddy Simulation (IDDES) model are validated where possible against time-mean wind-tunnel measurements, providing confidence in the simulation results. Indeed, the results show that due to the distinct flow features generated by estate-type geometries, the ground configuration only locally alters the flow field in close proximity to the ground, and therefore its impact on the flow near the automobile surfaces and in the wake is limited. Regarding the aerodynamic loadings, only the underbody surface pressure is found to be sensitive to the ground simulation, which leads to a variation in the lift coefficient by a factor of approximately two. However, the impact on the drag prediction is minimal, with the two drag coefficient predictions within 3% of each other, and consistent within the range of values from previous wind-tunnel tests.