Finite Rate Chemistry Large-Eddy Simulation of Self-Ignition in Supersonic Combustion Ramjet

In this study, large-eddy simulation is used to analyze supersonic flow, mixing, and combustion in a supersonic combustor equipped with a two-stage fuel injector strut. The present study focuses on mixing, ignition, and flame stabilization and the degree of detail required by the reaction mechanism in the large-eddy simulation model framework. An explicit large-eddy simulation model, using a mixed subgrid model and a partially stirred reactor turbulence-chemistry interaction model, is used in an unstructured finite volume setting. The model, and its components, has been carefully validated in a large number of other studies. To bestow further validation and to provide supplementary information about the physics of mixing and supersonic combustion, experimental data from the National Aerospace Laboratory of Japan's supersonic combustor, equipped with the two-stage strut injector and connected to ONERA's vitiation air heater, are employed. The large-eddy simulation predictions are compared with the experimental centerline wall pressure distribution and the planar laser-induced fluorescence imaging of hydroxide-ion radicals distributions in several cross sections of the combustor, showing excellent qualitative and quantitative agreements. The large-eddy simulation results are furthermore used to elucidate the complicated flow, mixing, and combustion physics imposed by the multi-injector two-stage injector strut. The importance of the combustion chemistry appears weaker than expected but with the one-step mechanism resulting in a too early ignition (caused by local shock wave heating) and a more stable flame, as compared with the more detailed two- and seven-step mechanisms.