Response of the Separated Flow over an Airfoil to a Short-Time Actuator Burst

Abstract

Experimental measurements of the flow structure evolving in the separated flow over an NACA 0009 wing at 12° angle of attack were obtained with particle image velocimetry, surface pressures, and force transducer measurements of the lift coefficient and pitching moment coefficient. Phase-averaged two-dimensional velocity field measurements provide details of the separated shear layer evolution following a four-pulse burst sequence from a synthetic jet actuator. The flow field development is quite similar to the observations made by Brzozowski, et al. (2010), who used a pulsed-combustion actuator that is orders of magnitude stronger than the synthetic jet. Proper orthogonal decomposition of the PIV data sets showed that the combination of the time-varying coefficients modes 1 and 2 correlate with the negative of the lift coefficient response. The surface pressure signals were correlated with the roll up and convection of the large-scale vortex structure that follows the actuator burst input. A spatially localized region of high pressure occurs below and slightly behind a "kink" that forms in the shear layer. A localized region of high surface pressure that follows the kinked region correlates with the lift reversal that occurs within 2.0t^+ after the burst signal was triggered.