Hybrid Reynolds-Averaged and Large-Eddy Simulation of Mixing in an Axisymmetric Scramjet

Abstract

An unsteady numerical simulation of a simple axisymmetric inlet-fuelled scramjet engine concept is performed using a hybrid Reynolds-averaged Navier-Stokes and large-eddy simulation approach with a low-dissipation numerical scheme. The freestream has a Mach number of 7.5 with Mach 8 flight enthalpy and a dynamic pressure of 48 kPa. The simulation is of a non-reacting case where hydrogen is injected into nitrogen. The simulation is used to provide a detailed description of the structure of the flow. The simulation shows that a large-scale pair of counter-rotating vortices forms within the scramjet combustor, with rotation opposite to the rotation of the pair that forms further upstream due to the interaction of the fuel plume with the crossflow. This vortex pair is found to signicantly alter the shape of the hydrogen fuel plume, and increase the rate at which the hydrogen is mixing by more than a factor of two compared to before the vortex pair is formed. The distribution of hydrogen is examined in detail, including instantaneous mole fraction, the time-averaged mole fraction, as well as root mean square of fluctuations of hydrogen mole fraction. The time-averaged and fluctuating wall pressures, the mean velocity eld, and resolved turbulence quantities are also examined. Additionally, the hybrid Reynolds-averaged Navier-Stokes and large-eddy simulation results are used to evaluate the performance of a steady-state Reynolds-averaged Navier-Stokes simulation of the conguration.