Closed- Loop Aerodynamic Flow Control of a Free Airfoil

Transitory flow arising from the dynamic response of a free-moving airfoil model to commanded pitch and plunge maneuvers is investigated in wind tunnel experiments. The airfoil is mounted on a 2-DOF traverse and its trim and dynamic characteristics are controlled using position and attitude feedback loops that are actuated by servo motors. Commanded maneuvers are achieved without moving control surfaces using bi-directional changes in the pitching moment over a range of angles of attack that are effected by controllable, nominally-symmetric trapped vorticity concentrations on both the suction and pressure surfaces near the trailing edge. Actuation is applied on both surfaces by hybrid actuators that are each comprised of a miniature [O(0.01c)] obstruction integrated with a synthetic jet actuator to manipulate and regulate the vorticity concentrations. The present work focuses on the transitory response of the flow to step-modulated changes in the actuation input while the model’s position is maintained using the system's controller. Flow control effectiveness is demonstrated by the closed-loop response in plunge to a momentary force disturbance which is analogous to the free flight response to a sudden gust.

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