Influence of Geometry and Fuel Injection on Thermoacoustic Instabilities in a Supersonic Cavity

This study numerically investigates thermoacoustic instabilities in a supersonic cavity-based combustor relevant to scramjet engine applications. Simulations explore the influence of cavity geometry (aft-wall angles of 22.5◦, 45◦, and 90◦, and length-to-depth ratios of 4 and 7) and fuel injection pressure (0.6 MPa to 1.8 MPa) on flow dynamics and combustion characteristics with hydrogen fuel. Non-reacting flow simulations reveal advection and acoustic oscillations within the cavity, with frequencies matching analytical predictions. The introduction of combustion suppresses low-frequency pulsations while stimulating high-frequency oscillations (15–20 kHz), with larger aft-wall angles promoting more intense vortical structures and higher frequency oscillations. Increasing fuel injection pressure leads to a non-linear response. Higher injection pressures induce a flow “choking” phenomenon and a shift towards lower frequency oscillations associated with large-scale vortex shedding, in comparison with lower injection pressures. The simulation results exhibit good agreement with experimental data, indicating the importance of both advection/acoustic oscillations and the complex interaction of flow dynamics, combustion, and fuel injection in shaping the thermoacoustic behavior of supersonic cavity-based combustors.