Effects of suppressing the 3D separation on the rear slant on the flow structures around an Ahmed body: Fid-Bau Portal

Effects of suppressing the 3D separation on the rear slant on the flow structures around an Ahmed body

Thacker, A. / Aubrun, S. / Leroy, A. / Devinant, P.

Abstract This work considers separated flow past ground vehicles. It consists in analyzing the effect of canceling the separation on the rear slant of an Ahmed body (inclined at 25°) on the different structures developing in the wake. In order to better understand the flow features when canceling separation by means of flow control for drag reduction, two model configurations were used: one with a sharp edge at the connection between the roof and the rear slant and the second one with a rounded edge preventing the rear slant separation. The different wake features were analyzed experimentally and compared for both configurations. Using PIV measurements, this study focuses especially on the longitudinal vortices developing at each side of the Ahmed body. The comparison between the two configurations showed a drag discrepancy of 10% while the lift level remains unchanged. The absence of the separation bubble on the rear window mainly affects the near rear wake that strongly contributes to the weaker drag level. Moreover, results showed that the absence of this separation does not impact on the mean locations of the lateral longitudinal vortices but more specifically on their vortical center intensity.

Highlights ► Experimental analysis of the flow behind an Ahmed body with a slant angle of 25°. ► Two models are used with a sharp and rounded edge at the roof/rear slant connection. ► Effect of suppressing the rear window separation on the others structures. ► Drag level is 10% smaller without separation on the rear window. ► Modification of the wake toric structures but no impact for longitudinal vortices.