Front–rear wheel interactions for a model vehicle: consequence for drag

The role of front wheels in wheel-vehicle aerodynamic interactions is investigated for a simplified square-back vehicle by changing the bluntness of the front wheels. The interactions between the rear wheels and the vehicle wake are varied by modifying the distance between the rear wheels and the vehicle base. This results in a significant increase of the base drag for decreasing rear wheel/vehicle base distance, and we show that this increase is very sensitive to the bluntness of the front wheels: the smaller the bluntness, the larger base drag increases. We show that the base pressure decreases, and therefore, the drag increment varies linearly with the upstream velocity seen by the rear wheels, of course, significantly influenced by the bluntness of the front wheels. The main mechanism responsible for these pressure drag changes is a mean mass transfer from the wake of the main body to the wakes of the rear wheels. Based on this understanding, a physical model is proposed to explain the scaling law observed experimentally.