Effect of leading-edge curvature on airfoil separation control

Separation control on NACA 0012 and NACA 0015 airfoils was compared under incompressible conditions, using leading-edge periodic excitation, in order to assess the effect of leading-edge curvature. Both lift and moment coefficients were considered to compare and analyse control effectiveness. In contrast to the relatively mild NACA 0015 trailing-edge stall, NACA 0012 stall was dominated by a leading-edge bubble-bursting mechanism that gave rise to alternating intervals of partial attachment and separation, but with no regular frequency. Low-amplitude excitation downstream of the bubble enhanced poststall lift and significantly attenuated the associated unsteadiness. In general, larger momentum coefficients were required for NACA 0012 separation control due to the large centrifugal acceleration of the flow around 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 high-excitation amplitudes with relatively low frequencies was effective on the NACA 0012, and this was believed to be associated with the large harmonic content of the evolving perturbations.