Parametric study on self-sustained oscillation characteristics of cavity flameholders in supersonic flows

Abstract

Large eddy simulations were performed to study cavity self-sustained oscillation characteristics in supersonic flows. Calculations use the hybrid Reynolds-averaged Navier–Stokes (RANS)/large-eddy simulation (LES) method to predict unsteady-state flowfields. The calculations consider the effects of various flow or geometry parameters, including the inflow boundary layer thickness, Reynolds number, freestream Mach number, three dimensionality, and cavity configurations (length-to-depth ratio and cavity aft wall angle included). The results show that thick inflow boundary layer changes the oscillation mechanism in high-Mach-number flows while affects little at low Mach number. Reynolds number has little influence on the oscillation mechanism and the resonance frequencies. The simulated results suggest that the coupling between the shear-layer dynamics and the cavity acoustics is greatly reduced at high Mach numbers. The physical mechanisms in cavity oscillations shift from the vortex-acoustics resonance mechanism (Rossiter's model) to closed-box acoustics mechanism with the Mach number increase. Calculations on three-dimensional (3D) cavity configurations have further verified the validity of the 2D calculation results. Increasing cavity length-to-depth ratio makes the resonance frequency bands more complex. Decreasing the aft wall angle does not change the resonance frequency modes a lot except in the high-Mach-number flow.