Frequencies of Transverse and Longitudinal Oscillations in Supersonic Cavity Flows

A supersonic flow over a rectangular cavity is known to oscillate at certain predominant frequencies. The present study focuses on the effect of the cavity length-to-depth () ratio on the frequency for a free-stream Mach number of 1.7. The pressure oscillations are measured by changing the ratio from 0.5 to 3.0, and the power spectral density is calculated from the temporal pressure signals for each ratio. The results demonstrate that the spectral peaks for an ratio of less than ~1 and greater than ~2 are accounted for by the feedback mechanisms of the transverse and longitudinal oscillations, respectively. The results also demonstrate that the spectral peaks in the transition (1 <~ <~ 2) are accounted for by either of the two feedback mechanisms of transverse and longitudinal oscillations; that is, the flows under the transition regime oscillate both transversely and longitudinally.