Phase evolution of flow controlled by synthetic jets over NACA 0025 airfoil

The phase evolution of a separated boundary layer whose separation has been delayed using synthetic jet flow control is presented. Particle Image Velocimetry measurements were made for four control cases corresponding to high and low momentum addition with excitation frequencies targeting the shear-layer and wake instabilities. Coherent structures resulting from this control, their evolution and effect on the wake development are visualized. The excitation frequency of the synthetic jets and the strength of the synthetic jets significantly affect the response of the phase-averaged shear layer, leading to distinct mechanisms of separation delay. Increasing the frequency or the jet strength increases the length of the reattached flow.