Forces and flow structures on a simplified car model exposed to a transient crosswind

Abstract

A squareback simplified car model is exposed to a forced oscillating yaw and results are compared to static measurements. Tests are conducted at Reynolds number Re=3.7x105 and a maximum Strouhal number =0.053. Phase average force and moment measurements exhibit a phase shift between static and dynamic tests that increases with oscillating frequency. To gain better understanding of the origin of the phase shift phenomenon, this paper proposes to characterize the flow evolution around the model using PIV measurements. Phase-shift seems to originate from the pressure recovery area where velocity fields exhibit a time delay in their response to dynamic yawing. Moreover, lateral vortical structures appearing on lee side from =15° increase this phase-shift and consequently appear to be favourable to the lateral stability of the vehicle.