THE EFFECT OF ACOUSTICS ON FLOW PASSING A HIGH-AOA AIRFOIL

In this paper a study is presented of the separated flow properties an d corresponding aerodynamic behaviors of a high-AOA, NACA 63(3)-018 ai rfoil under internal acoustically pulsing excitation in a subsonic win d tunnel. The measurements by means of pitot-static pressure tube and hot-wire anemometer include the boundary layer velocity profiles, boun dary layer velocity energy spectra and velocity defect profiles in the wake. Results indicate that the acoustic excitation technique is able to alter the flow properties and thus to improve the aerodynamic perf ormance, especially when the airfoil is fully stalled at high AOA. Aft er the flow is effectively excited, the developed boundary layer delay s its separation from the surface. The most effective excitation frequ ency is found to be equal to the shear layer instability frequency whe n the airfoil is around at the post-stall angle; however, it becomes o f the vortex shedding frequency of the wake when the airfoil's AOA is increased beyond the stall. Data also show that the higher the pulsing acoustic level is, the better the flow properties are improved. (C) 1 997 Academic Press Limited.