Active Flow Control of Dynamic Stall by Means of Jet Flow at Reynolds Number 106

Abstract

In this study, we have examined slot location and velocity ratio of a tangential co-flow jet in dynamic stall motion of an airfoil at Reynolds number 1×106, for active flow control (AFC) purposes. The airfoil is the symmetrical NACA 0012 with a pitching motion between AOAs 5 deg. and 25 deg. about its quarter-chord with a sinusoidal motion. We have utilized Computational Fluid Dynamics (CFD) tool to numerically investigate the impact of jet location and jet velocity ratio on the aerodynamic coefficients. We have placed the jet location upstream the counter clock-wise (CCW) vortex which is formed during the upstroke motion near the leading-edge. We have also selected several other locations nearby to perform sensitivity analysis. Our results showed that placing the jet slot within a very small range upstream the CCW vortex has tremendous effects on both lift and drag, such that maximum drag which occurs at maximum incidences reduced by 80%. There was another unique observation: putting jet at separation point leads to an inverse behavior of drag hysteresis curve in upstroke and downstroke motions. Drag in downstroke motion is significantly lower than upstroke motion, whereas in uncontrolled case the converse is true. In addition, by implementing jet flow lift is significantly enhanced during both upstroke and downstroke motions. Finally, it should be indicated that this study provides initial steps in investigations of applying synthetic jet actuator (SJA) on a pitching airfoil at high Reynolds number 106 with effects of changing momentum ratio and SJA frequency, which will be presented in the near future.