Bi-stable flows past road vehicles and controlling mechanisms

The wake bi-stability behind a notchback Ahmed body geometry was investigated by performing wind tunnel experiments and Large-eddy simulations (LES). In both approaches, the bi-stable nature showed two stable mirrored states characterized by a left or right asymmetry for long periods. The asymmetry of the flow was ascribed to the asymmetric separations and reattachments in the wake. The mechanism responsible for the stochastic switch between two asymmetric mirrored wake states were explored from the perspective of near-wall flow structures. Modal analysis applying Proper Orthogonal Decomposition (POD) was employed for the analysis of the wake dynamics. The bi-stable phenomenon was found sensitive to the rear effective backlight angle, blockage ratios, yaw angles, and other terms resulting in the change of the wake flow. The flow control of the bi-stable wake was achieved by producing near-wake perturbations in the shear layer for suppression of the bi-stability. The symmetrization of the wake was observed with the vortex generator placed on the centre of the roof, producing vortices interacting with separations attached to the rear slanted surface.