Nonlinear Characteristics of a Rectangular Cavity in Supersonic Flow

Time-resolved schlieren images and unsteady pressure measurements were employed to understand the flowfield characteristics of a rectangular cavity at Mach number 1.8 with a unit Reynolds number of 7.3x107. It was illustrated that the vortex dynamics in the cavity shear layer were found to be nonlinear, where the vortex speed was observed to be varied from 0.50U infinity to 0.59U infinity with an average value of 0.55U infinity. Unsteady pressure measurements inside the cavity revealed six tones, among which the third tone was dominant. The uniqueness of the flow features both outside as well as inside the cavity was studied for one vortex shedding cycle. Analyses using different techniques divulged that the occurrence of the first and second tones was due to wave propagation and vortex shedding, respectively. On the other hand, frequency that corresponds to one time period was correlated to the third tone. Further investigations unveiled that the entrainment of freestream between shear-layer vortices generated type 5 acoustic waves, which were responsible for the production of other cavity tones. The wavelet analyses indicated that the frequencies were amplitude modulated in time, and the wavelet spectra of the second and third tones contain high-energy events along with sporadic distribution of low-energy events without mode switching phenomenon.