Flow and Combustion in a Supersonic Cavity Flameholder

Simulations of both inert mixing and sustained combustion are analyzed for a cavity flameholder based on corresponding experiments. An M 1 round ethylene jet fuels a cavity with length-to-depth ratio L∕D 3.5 and a 45° inclined downstream wall. Oxidizer mixes into the cavity from the M 3 core flow. The simulations reproduce shock angles and wall pressures of the corresponding experiment. The effects that cavity combustion has on the core-flow gas dynamics and cavity entrainment are analyzed in detail. Relative to the inert case, heat release leads to a complex core flow, with upstream boundary layers transiently separating and highly unsteady shocks over the cavity. Their collective effect is the formation of a virtual throat, which decreases the core flow to M 2 above the cavity. Lagrangian trajectories assess the roles that turbulence, combustion, and three-dimensional side-wall boundary layers have on oxidizer entrainment into the cavity. Overall, sustained cavity combustion suppresses entrainment by a factor of about 2.