Transient Feature of Flow Field in Wake of Ahmed Body

Abstract:

Compared with the published data, the validity of the large eddy simulation method is verified. The large eddy simulation method is applied to the study of the flow field around slanted surface and rear vertical base of the Ahmed body with a slant angle of 25°at high Reynolds number. This work aims to gain a relatively thorough understanding of the transient features of the predominant coherent structures around the Ahmed body by sampling flow field information and spectrum analyses of a recirculation bubble over the slanted surface, one pair of counter-rotating longitudinal C-pillar vortices originating from the two side edges of the rear window, and a recirculation torus behind the vertical base. In different regions of flow field, the transient features of the wake are different. The flapping motion of the recirculation bubble over the slanted surface corresponds to an absolute unsteadiness while the activity of the coherent structures is convective. The pair of C-pillar vortices coupled with the spanwise vortices over the slanted surface are symmetric. However, they only mix with the recirculation torus behind the vertical base resulting in asymmetric characteristic. The rolling up and shedding of the recirculation torus behind the vertical base are similar to Karman vortex street. At high Reynolds numbers, the characteristic frequency of different regions tends to be consistent.