Active flow control of a wing section in stall flutter by dielectric barrier discharge plasma actuators

This paper investigates the potential of using an active flow control technique to modify stall flutter oscillations of a NACA (National Advisory Committee for Aeronautics) 0015 wing section. Wind tunnel experiments have been performed with a test-rig that provides the elastic degree of freedom in pitch. Measurements of the clean airfoil are taken at preset angles of theta(0) = 6 degrees - 12 degrees, and for Reynolds numbers of Re-c = 6.2 x 10(4) - 1.25 x 10(5), which reveal the dependency of the stall flutter oscillations to Re-c and theta(0). Then, flow control experiments are carried out at theta(0) = 10(o) and Re-c = 1.04 x 10(5). Two dielectric barrier discharge plasma actuators have been employed simultaneously to exert dual-point excitation to the baseline flow. It is shown that during the upstroke half-cycle, plasma actuation postpones the dynamic stall of the airfoil and increases the maximum pitch angle of the stall flutter cycle. On the downstroke, dual-point excitation effectively improves the rate of pitching moment recovery and leads to flow reattachment at a larger pitch angle. Normalized excitation frequencies F-ex = f(ex)/f(w) (where f(w) is the wake mode frequency of the stalled airfoil) ranging from 0.1 up to 3 have been examined. Among the controlled cases, excitation with F-ex = 0.6 and F-ex = 2.2 provides the largest and smallest pitch amplitude, respectively, and the case of F-ex = 3 demonstrates the most impact on flow reattachment. Finally, it has been concluded that the employed control strategy is effectively capable of modifying the dynamic stall process and associated pitching moment. However, a more sophisticated control strategy would be required to significantly mitigate the stall flutter oscillations.