Computational Investigation of Thermal Nonequilibrium Effects in Scramjet Geometries

Abstract

To characterize the impact of thermal nonequilibrium in shock-induced combustion scramjets, several thermal equilibrium and nonequilibrium computational fluid dynamics simulations have been performed. Specifically, the effects that would be encountered in shock-tunnel testing are of interest. Therefore, thermal equilibrium and nonequilibrium simulations are run for a Mach 6 shock-tunnel nozzle and a radical farming scramjet model with total enthalpies between 3.3 and . Simulating both the nozzle and scramjet with thermal nonequilibrium represents the shock-tunnel test, whereas equilibrium inflow into a scramjet simulated in thermal nonequilibrium provides the scenario encountered in actual flight. For all nonequilibrium simulations, the Landau–Teller model in combination with modified Millikan and White thermal relaxation coefficients is used. It is shown that modeling the entire flow as being in thermal equilibrium results in higher effective temperatures within the local high-temperature regions where ignition occurs, which causes the ignition length to decrease and thus the combustion process to be more efficient compared with the nonequilibrium cases. Additionally, the conditions for ignition in simulations representing shock-tunnel experiments are found to be more favorable than in the simulations representing a flight test, assuming the same enthalpy and boundary conditions. Furthermore, these differences are found to be insensitive to the total enthalpy.