Feedback mechanism in supersonic laminar cavity flows

The mechanism driving the self-sustained oscillations in supersonic laminar cavity flows is studied to be a feedback-loop mechanism between the discrete vortices and acoustic disturbances. Implicit large eddy simulations (ILESs) are conducted. One typical feedback cycle is visualized with phase-averaged flowfields. The feedback compression waves are radiated from the region near the cavity trailing lip. Their generation is related to the passage of large-scale vortices over the trailing edge. In phase of acoustic excitation near the cavity leading edge, the incoming boundary layer rolls up into two well-originated vortices with highly two-dimensional characteristics and strong spanwise coherence. Vortex pairing seems to occur between these two discrete vortices. Phase averaging is shown to be a superior approach for the analysis of cavity oscillations.