Interactive Control of a Turbulent Separated-and-Reattaching Flow

This paper describes results of an experimental study on an interactive control of a turbulent separation bubble formed by the separation from the leading edge of a blunt circular cylinder. Reynolds number based on the main-flow velocity and the diameter of the cylinder was 6.9×104. The fluctuatinn velocity at the edge of the shear layer near the separation edge was supplied to a woofer installed inside the cylinder, which introduced a disturbance into the shear layer through a thin slit. The reattachment length was found to decrease with increasing phase lag θ between the velocity and the input to the woofer if 0°≤θ≤160°. This change was associated with a change in the vortex merging in the shear layer. The flow in the separation bubble experienced intermittent large-amplitude oscillation when θ≥160° or when the forcing frequency is in a certain range. This implies that the flow tends to become unsteady under the interactive control.