Control of Poststall Airfoil Aerodynamics Based on Surface Perturbation

This paper presents an experimental investigation on the control of airfoil aerodynamics at poststall angle of attack α using a surface perturbation technique. Piezoceramic actuators were deployed to create a local surface perturbation on a NACA0012 airfoil, along with an open-loop control system, to manipulate flow around the airfoil. Two different control signals were examined, i.e., square and sine waves. Whereas the lift and drag forces were measured using a load cell, the flow was documented using a particle image velocimetry, laser Doppler anemometer and a single hot wire. The surface perturbation significantly improved the airfoil aerodynamics for 12 ≤ α ≤ 20 deg. The control effect with the square-wave excitation was found to be much more effective than that with the sine wave. The control was most effective at α = 14 deg: the mean lift coefficient, lift-to-drag ratio, and figure of merit (i.e., the ratio of the power to aerodynamic efficiencies) were enhanced by 35, 64, and 44%, respectively, whereas the mean drag coefficient dropped by 23%. Furthermore, the airfoil stall was postponed by 3 deg. The physics behind the observations were discussed in detail.

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