Salient features of wheel-vehicle aerodynamic interactions: Consequences for drag

Salient features of wheel–vehicle interactions and their consequences for drag are investigated experimentally based on a simplified square-back vehicle with different distances l between the rear wheels and the base of the vehicle. Two different mechanisms responsible for a base drag increase of up to 12% are distinguished. At the scale of the vehicle, whatever the distance l, wheels perturb the underflow and induce a global variation of the vertical balance of the vehicle wake. According to the state of the initial wake, significant base drag increase or decrease are observed. Considering the scale of the wheels, if the wheel-to-base distance l/w (w being the width of the wheels) is smaller than a threshold of order 3 in the present configuration, the base drag increases and is very sensitive to l/w. In this situation, a mean mass transfer from the vehicle wake to the wake of the rear wheels is observed. Based on these observations, a physical model is then proposed to explain this high-sensitivity regime. •Varying distances between rear wheels and base of a square-back model are considered.•Rigid rotating wheels having sharp or round shoulder are used.•Two different mechanisms induce a base drag increase of up to 12%.•At the global scale of the vehicle, wheels alter the vertical balance of main wake.•Local interactions cause a mean mass transfer from main wake to rear wheel wakes.•A physical model is proposed to explain these interactions.