Effect of Leading-Edge Curvature on Airfoil Separation Control

Separation control on NACA 0012 and NACA 0 015 airfoils was compared under incompressible conditions,using leading-edge periodic excitation, in order to assessthe effect of leading-edgecurvature. Both lift and moment coefcients were considered to compare and analyse control effectiveness. In contrast to the relatively mild NACA 0015 trailing-edge stall, NACA 00 12 stall was domina ted by a leading-edge bubble-bursting mechanism that gave rise to alternating intervals of partial attachment and separation, but with noregular frequency. Low-amplitude excitation downstream of the bubble enhanced poststall lift and signi cantly attenuated the associated unsteadiness. In general, larger momentum coefcients were required for NACA 0012 separation control due to the large centrifugala cceleration of the owaround the leading edge. Because of the different stalling characteristics, relatively high- and low-excitation frequencies were effective for the NACA 0012 and NACA 0015 airfoils, respectively.However, the combination of highexcitation amplitudeswith relatively low frequencies waseffective on the NACA 0012, and this was believed to be associated with the large harmonic content of the evolving perturbations.