Inlet Conditions and Fuel Effects on Structures in Backward-Facing Step Combustor

The flame structure in solid-fuel ramjet (SFRJ) combustors is strongly influenced by inflow conditions, including unsteadiness, boundary-layer development, and inflow speeds. This study examines a backward-facing step configuration using a high-fidelity discontinuous Galerkin implicit large-eddy simulation solver coupled with the flamelet progress variable approach. A series of 30 simulations are conducted to investigate the influence of inflow conditions on the flow and flame structure within the reactor. We explore how variations in inlet velocity fluctuations, flow speeds, and boundary-layer growth affect vortex shedding and the recirculation zone under varying conditions. The inert cases are validated against experimental data and provide a baseline for comparison to reacting conditions. Fuel addition is shown to influence flow structure, extending the recirculation zone and reducing vortex shedding frequencies. When the flow is ignited, the recirculation zone expands slightly, and vortex shedding frequencies become less coherent, while the Reynolds number in the poststep region declines. Finally, inflow development increases the flame brush size, enhancing mixing at the expense of reduced fuel residence time. These findings highlight the critical role of inflow conditions in shaping downstream flame characteristics.