The present study investigates the modifications of cavity shear layer by a horizontal cover plate, having different leading-edge profiles, above the cavity. All the experiments were performed in a recirculating water channel. The free stream velocity is maintained at 20 cm/s, however, the Reynolds numbers, based on the momentum thickness at the upstream edge of the cavity, are kept about Re{sub}(θo) = 171±5 and 102±6.3. In the present study, the shift of oscillating mode is primarily determined by the amount of flow acceleration along the gap between the cover plate and the cavity. However, the enhanced oscillating amplitude is triggered by higher velocity fluctuating level, created by the boundary layer adjacent to the cover plate. Furthermore, deflection of the shear layer into the cavity, caused by the growth of the boundary-layer thickness adjacent to the cover plate with blunt leading-edge profile, increases the strength of the feedback and thus also contributes to the enhancement of the oscillating amplitude across the cavity.
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