Modal analysis of oblique shock-induced flow dynamics in a supersonic reacting shear layer

Abstract: Efficient mixing in high-speed compressible flows, crucial for scramjet operation, can be significantly enhanced by shock wave interactions. This study employs Direct Numerical Simulations (DNS) to comprehensively examine the interaction between an oblique shock and a spatially developing turbulent mixing layer, contrasting inert and reacting (hydrogen-air combustion) cases. Utilizing streaming Dynamic Mode Decomposition (sDMD), we analyze four configurations: inert and reacting shear layers, both with and without shock impingement (at $\mathrm{Ma}_c = 0.48$). We evaluate the temporal mode growth rates, the evolution of vorticity thickness, and the spatial structures of dominant DMD modes to elucidate how shocks and heat release synergistically influence flow stability, mixing, and the underlying coherent dynamics. Results reveal that the oblique shock significantly amplifies Kelvin-Helmholtz instabilities, excites a broader spectrum of unstable temporal modes, and accelerates the growth of the vorticity thickness. Combustion-induced heat release further modifies this response, leading to a redistribution of energy among the DMD modes and indicating a complex coupled effect with shock dynamics, particularly in the enhanced excitation of high-frequency modes and the alteration of spatial structures. The modal analysis identifies distinct frequency bands associated with shock and combustion effects and characterizes the dominant spatial patterns, offering refined insights for controlling and enhancing mixing in high-speed propulsion flows.