Use of Periodic Excitation to Enhance Airfoil Performance at Low Reynolds Numbers

Abstract

throughout the entire cycle because of attachment of the  ow to the  ap. In contrast,however, instantaneousdCL=d® is not signiŽ cantly affected. In addition to lift increases, the light-moment stall is eliminated, resulting in a 20% reduction in moment excursions, while excitation induces a further mean nose-down pitching moment of CM;mean » 0:05: Although intrinsically different from the preceding case, a similar control strategy was applied for  ap-shoulder excitation. Here, excitation is initiated soon after the commencement of pitchup and terminated in the region where the continuous excitationdownstroke lift data begin to increase.As indicated in the Ž gure, this control strategybroughtabout the maximumpossiblelift excursions, namely between the minimum baseline and maximum excitation limits (CL ;exc D 0:8). In addition, the light-moment stall, which was effectively eliminated by continuous excitation, is also eliminated by intermittent excitation.