Characteristics of Oscillations in Supersonic Open Cavity Flows

Characteristics of oscillations in supersonic open cavity flows are investigated numerically using hybrid RANS/LES (Reynolds-Averaged Navier-Stokes/Large Eddy Simulation) method. The oscillation regimes and feedback mechanisms for the supersonic cavity flows are identified and analyzed. The calculation captures a mixed shear-layer/wake oscillation mode in the flow of Ma = 1.75, where these two modes occur alternately. The shear-layer mode and wake mode are driven by vortex convection-acoustic feedback and absolute instability, respectively. In particular, the results indicate that the feedback-acoustic-wave in the shear-layer mode is probably generated by the reflection of the downstream-traveling pressure wave, associated with the shed vortex in the shear layer, on the aft wall. The cavity flow of Ma = 2.52 is then simulated to see the influence of Mach number. It is found that the increase of Mach number may decrease the amplitude of the fluctuations in the shear layer, inhibiting the transition to wake mode. Furthermore, the influence of upstream injection is also studied, where the results show that the injection only weakens the oscillations and faintly shifts the resonant frequencies.