Modal analysis of actively controlled flow past a backward facing ramp

Spectral proper orthogonal decomposition (SPOD) is applied to pressure measurements to further elucidate properties of separated flow behind a backward facing ramp in uncontrolled and controlled conditions. Four major modes have been identified in uncontrolled conditions associated with the presence of large-scale roll-up vortices including flapping motion of the recirculation region, large-scale vortex emission at the slant edge, and onset of Kelvin-Helmholtz instability. The control suppresses recirculation mode and all associated mechanisms. The SPOD mode associated with jets actuation allows one to analyze the extension of the receptivity region of the flow to the action of control.