Influence of vehicle back shape on wheel-vehicle aerodynamic interactions: a model study

The influence of vehicle back shape on wheel-vehicle aerodynamic interactions is investigated in a model situation. A pair of D-shaped obstacles is placed under a fast-back or a square-back Windsor body to mimic the blockage of the wheels and to induce near-wake interactions at the base of the body. By varying the distance l between the obstacles and the base of the body, the consequences of near-wake interactions are analyzed for both geometries. For both bodies, when the obstacle-to-base distance is small l/d<2.5 (d is the width of the obstacles), a mean mass transfer from the main body wake to the obstacle wakes is measured which is responsible for a base drag increase of up to 18% . For identical settings of the obstacles, both mass transfer and drag increase are not sensitive to the shape of the model. This observation is analyzed using both experimental and numerical data. On the other hand, the mean wake topology of the fast-back body is found to be much less sensitive to the obstacles compared to the square-back body.