Flow choking in a combustor is a potential threat to the stable operation of a scramjet, especially at low inflow Mach number. In this paper, a numerical study is conducted to investigate the flow choking mechanism in a cavity-based supersonic combustor with a low inflow Mach number (Ma = 1.5). The compressible combustion code PeleC with the block-structured adaptive-mesh-refinement method is used as a calculation tool. The findings suggest that flow choking is triggered even with a localized heat release, which is different from the thermal choking occurring with a relatively high inflow Mach number. The dominant flow choking mechanism under low inflow Mach number can be attributed to the coupling effect of viscous dissipation, heat addition, mass addition, and shock wave compression (VHMS). The slow turbulent mixing process induced by low-speed flow leads to the transition of flame stability modes from a recirculation zone/shear layer (RZ/SL) mode to a recirculation zone/jet wake (RZ/JW) mode. RZ/SL-to-RZ/JW transition enhances VHMS coupling effect, which ultimately triggers the flow choking above cavity. A long cavity accelerates flow choking formation by enhancing VHMS coupling effect. On the other hand, the presence of a cavity serves as a pressure buffer zone under complete choking condition. A longer cavity effectively restrains the development of flow choking by creating a larger buffer area. The design of the cavity length should be approached with greater caution in order to achieve a delicate balance between flow choking, combustion efficiency, flame stability, and geometric complexity.
Jin et al. (Sun,) studied this question.