Effect of pressure gradient on flow instability in the subsonic–supersonic mixing layer

Abstract

In accordance with high-speed schlieren results, the flow instabilities in the subsonic–supersonic mixing layer with a convective Mach number of 0.19 are investigated in detail. In the incipient stage of the mixing layer, wave structures caused by the pressure gradient affect the evolution of the Kelvin–Helmholtz vortexes. The dynamic mode decomposition (DMD) analysis reveals that the pressure gradient from the subsonic side to the supersonic side promotes flow instability. At this time, the Kelvin–Helmholtz vortexes mode is found to be dominant. A high temporal resolution is proven to play an important role in the DMD analysis to capture high-frequency modes.