Closed-Loop Dynamic Stall Control Using a Plasma Actuator

A closed-loop plasma-actuated control scheme that relies on the ability to detect incipient flow separation is presented. It is based on the heightened receptivity of the boundary layer to disturbances at the onset of flow separation. A plasma actuator introduces periodic disturbances into the flow at a low-powered "sense state". A pressure sensor measures the resulting pressure fluctuations close to the leading edge. When the sensed pressure fluctuations exceed a predetermined threshold level, the plasma actuator is switched to a high-powered "control state" that is designed to reattach the flow. The method provides not only a precursor for flow separation but also an indicator of when conditions exist where active flow reattachment is no longer needed. This is demonstrated on a periodically oscillating airfoil that is pitched into "light" and "deep" dynamic stall. The performance of the closed-loop scheme is evaluated by comparing the aerodynamic loading parameters to the baseline and open-loop unsteady controlled cases. In light dynamic stall, control over only 11.2% of the pitch cycle increased the cycle-integrated lift by 12% and reduced the maximum nose-down moment by 60%. In addition, it produced a positive net-cycle damping that was otherwise negative without feedback control.