Computational Study of Aero-acoustic Feedback in Supersonic Cavity Flow

Abstract

Experimental and computational analysis has been already carried out by many researchers on supersonic flow past cavities, but detailed analysis of computational results still needs some insight. For this purpose, an open rectangular cavity with a length to depth ratio of 2 ($L/D = 2$) and inlet Mach number 1.71 was considered for an unsteady computational analysis in ANSYS FLUENT, using SST $k-\omega$ turbulence model. The two dimensional structured grids were generated in Pointwise grid generation software. FFT using Power Spectral Density (PSD) was carried out on the unsteady pressure data for 10,000 time-steps, with a total flow time of 10 ms. Many modes were observed, with dominant frequency at 10.5 kHz. The mode frequencies obtained were validated from experimental results and from the corresponding Rossiter’s Modes. Correlation between the unsteady pressure data was also found to analyze the flow dynamics. Many flow visualization techniques were employed such as density gradient-based numerical schlieren, which revealed many flow features associated with the flow. Vortex Shedding Visualization was carried out in terms of the lambda 2 criterion, where the vortex core ($\lambda _2 < 0$) can be observed moving downstream in the shear layer. Lastly in the acoustic pressure contour, an acoustic wave can be observed moving within the cavity. The analysis was extended for different shapes of subcavities on the front and aft wall. As the front wall subcavity act as a passive control device, reducing the overall sound pressure level inside the cavity, whereas the aft wall subcavity acts as a passive resonator with distinct harmonic fluid-resonant modes. A more detailed analysis on these configurations with different shapes will give a comparative and better understanding on the flow features, mode frequencies, Rossiter’s coefficients, and fluid-resonant oscillations in a supersonic cavity. Also, the applicability of Rossiter’s Modes has been compared with the Closed-Box acoustic model for different configurations.