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 (L/D) ratio on the frequency for a free-stream Mach number of 1.7. The pressure oscillations are measured by changing the L/D ratio from 0.5 to 3.0, and the power spectral density is calculated from the temporal pressure signals for each L/D ratio. The results demonstrate that the spectral peaks for an L/D ratio of less than similar to 1 and greater than similar to 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 <similar to L/D <similar to 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.