A Backward-Facing Step (BFS) is widely used as an in-vitro model to investigate the influence of flow separation and recirculation observed in biomedical devices, arterial bifurcations and stenoses. In this study we numerically investigate the flow over a BFS with an expansion ratio of 2 and pulsed velocity at the inlet. The main objective is to study the effects of oscillation frequency and amplitude on flow evolution and interaction between vortices. The pulsatile flow leads to a breakdown of the primary recirculation vortex and the generation of a secondary upper wall instability at lower Reynolds numbers than in the steady case. The results show that the amplitude coefficient plays a dominant role in the primary vortex formation but the frequency determines the amount of circulation convected downstream.

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