Investigation on the effect of horizontal and vertical deflectors on the near-wake of a square-back car model

The near-wake flow field downstream of a square-back car model is analyzed to investigate on the combined effect of horizontal and vertical deflectors. Aerodynamic coefficients and near-wake velocity fields are presented for a range of deflectors size and slant angles, for Reynolds number Re ≈ 250,000 based on free stream velocity and model height. Mean velocity fields and turbulence quantities are shown to shed light onto the interactions taking place within the wake. The underlying rationale is to couple a decrease of the wake extent along the vertical direction, achieved by reducing the size of the top separated region, to a simultaneous reduction of the fluctuations in the horizontal plane induced by the lateral longitudinal vortices. Vertical deflectors height is reported to play a key role in this scenario markedly affecting the resulting drag and lift coefficients. Analysis of velocity fields points out the existence of an optimal vertical spoiler size, in the presented set-up equal to 2/3 of model height, which features the overall best performance compared to other tested configurations. The beneficial effect of combined spoilers is found to be more relevant when horizontal and vertical deflectors feature a moderate (20°) slant angle with respect to free stream direction.