Numerical Simulation of Scram-Mode Operation of an Axisymmetric Combustor in an Arc Tunnel

Large-eddy simulations of scram-mode operation of an axisymmetric inlet–isolator–combustor configuration experimentally tested in the ACT-II arc-heated combustion tunnel are presented in this work. A 32-species ethylene oxidation mechanism including nitric oxide decomposition reactions is used for most calculations; sensitivities due to the use of a 43-species model are also assessed. Numerical flame stabilization under conditions of the experiment (Mach 4.5 inflow, equivalence ratio of 0.82) is a sensitive function of the rate of energy release within the combustor. This can be altered by changes in the inflow oxygen atom composition (using values obtained from simulations of the arc heater itself) and the choice of reaction mechanism, but even with these controls, it was found necessary to threshold the pressure level supplied to the reaction rates to achieve stable supersonic combustion within the unit. The results presented show a strong sensitivity to these controlling factors in that good agreement with experimental trends can be obtained for specific combinations, but the prescription is not unique. The predictions show that scram-mode operation occurs under lean premixed conditions, characterized by a predominance of CO, little formation of [Formula: see text], an appreciable temperature rise, and an OH signal that rises substantially before increases in the formation rates of the major combustion products.