Exploratory RANS and LES simulations of transient supersonic combustor flow

Numerous physical mechanisms that dominate the performance of supersonic combustion devices remain poorly understood. These include fuel-air mixing processes, ignition initiation and extinction, flame holding and effect of off-design variation on these phenomena. Since ground and flight tests are very difficult to perform in this environment, simulations play a key role in augmenting development. However, several uncertainties arise in the modeling and inter-pretation of numerical simulations. In addition to accuracy and physical consistency issues, simplifying assumptions play a major role in the interpretation of the results. In this paper, exploratory simulations are described with unsteady Reynolds Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) for initial combustion phenomena in a generic circular cross-section combustor employing an axisymmetric cavity flameholder. Both frozen and finite rate chemical kinetics are considered, the latter with a 20-reaction, 13-specie model for ethene-air mixture. The injection strategy chosen is motivated by prior parametric studies on rectangular scramjets. The arrangement consists of eight injector pairs distributed at equal angular distances around the cavity. The first set of eight is located on the floor of the cavity and inject radially inward, (normal to the surface and the freestream). The second set of eight is located on the inclined downstream ramp and inject in the direction opposite the main flow. The inflow is assumed to be an averaged (uniform) profile obtained from a “scoop ” inlet. The significant differences between RANS and LES in th