Control of the separated-and-reattaching flow over either a backward-facing step or a cavity by film actuators

An experimental investigation aimed at controlling the separated-and- reattaching flows over either a backward-facing step or a cavity is carried out. Thin film actuators, attached to the step surface at the edge, are used for the control. Experimental results show that this system is capable of controlling the separation flow of a backward-facing step when the freestream velocity is under 15m/s. The phase of the separation can be altered in the spanwise direction. The effect of the control is preserved past the reattachment point. Elowever, the systematic pattern of velocity fluctuation cannot be maintained when the freestream velocity is higher. For the flow over a cavity, the flow is controllable when the freestream velocity is low. However, at a high freestream velocity (20 m/s), the uniform phase mode becomes dominant and the flow becomes difficult to control.