Control of Dynamic Stall over a NACA 0015 Airfoil Using Plasma Actuators

Dynamic stall is observed in numerous applications, including sharply maneuvering fixed-wing aircraft, biomimetics, wind turbines, and most notably, rotorcraft. The associated unsteady loading can lead to aerodynamic flutter and mechanical failure in the system. The present work explores the ability of nanosecond pulse-driven dielectric barrier discharge plasma actuators to control dynamic stall over a NACA 0015 airfoil. The Reynolds number, reduced frequency, and excitation Strouhal number were varied over large ranges: Re = 167,000-500,000, k = 0.025-0.075, and St(e) = 0-10, respectively. Surface pressure measurements were taken for each combination of Reynolds number, reduced frequency, and excitation Strouhal number. Phase-locked particle image velocimetry measurements were acquired for select cases. It was observed that the trends of effect of St(e) were similar for all combinations of Reynolds number and reduced frequency, and three major conclusions were drawn. First, it was observed that low Strouhal number excitation (St(e) < 0.5) results in oscillatory aerodynamic loading in the stalled stage of dynamic stall. This oscillatory behavior was gradually reduced as Ste increased and was not observed beyond St(e) > 2. Second, all excitation resulted in earlier flow reattachment. Last, it was shown that excitation, especially at high St(e), resulted in reduced aerodynamic hysteresis and dynamic stall vortex strength. The decrease in the strength of the dynamic stall vortex is achieved by the formation of large-scale structures induced by the excitation that bleed the leading-edge vorticity before the ejection of the dynamic stall vortex. At sufficiently high excitation Strouhal numbers (St(e) approximate to 10), the dynamic stall vortex was completely suppressed.