Influence of the rounded rear edge on wake bi-stability of a notchback bluff body

Abstract

The wake bi-stability behind notchback Ahmed bodies is investigated by performing wind tunnel experiments and large eddy simulations (LESs). The focus of this study is on the suppression of bi-stable wakes achieved by rounding the roof's trailing edge of the body. The suppression effect is found to depend on the Reynolds number (Re). The wake behind a sharp edge remains bi-stable for all tested Re. However, for a rounded edge with small radius, wake bi-stability at Re=0.5×105 and wake symmetrization with 0.75×105≤Re≤1.5×105 are observed. Increasing Re with Re≥1.75×105, the wake returns to the bi-stable state. Particularly, with Re≥2×105, a stable asymmetric wake state with no switches is observed for long periods. Performing LES confirms the expected wake asymmetry at Re=0.5×105 and symmetry at Re=1×105 for the case of rounded edge with a small radius. Besides, another wake symmetry is observed for the rounded edge with a large radius at Re=0.5×105. For the two wake symmetries shown in the LES results, the symmetrization is attributed to wake suppression in the notchback region, forcing the flow separation from the rear roof to attach to the slant on both sides of the body.