Mode Behavior in Supersonic Cavity Flows

The behavior of oscillation modes in a supersonic flow of a Mach number of 1.58 over a cavity of L/D=2 and L/W=0.89 was studied using wind-tunnel experiments. Through instantaneous shadowgraph visualization, the leading-edge shock and trailing-edge shock were both found to be at antiphase to one another for the first mode. Simultaneous unsteady pressure measurements were carried out at the front and aft walls of the cavity. From a wavelet analysis, the dominant mode was found to be the second mode, which prevailed for a major duration of the measurement time. Mode switching was observed between the first and second modes of oscillation. The mean velocity of the vortical disturbance convecting downstream and the acoustic disturbance travelling upstream inside the cavity was determined from a cross-correlation analysis. An examination using wavelet coherence revealed the coherence and phase difference existing between the pressure signal at the front and aft walls. The phase difference estimated from the measurements indicated the strong influence of cavity acoustic resonance on the cavity oscillations. However, the phase difference values showed a slight deviation between the acoustic resonance and cavity modes owing to the standoff distance between the trailing-edge shock and the aft wall.