Numerical simulation of thermal choking of a channel during combustion of a hydrogen-air mixture in a supersonic flow

Results of simulations of a high-velocity reacting flow of a non-premixed hydrogen-air mixture in a channel with sudden expansion in the form of backward-facing steps with transverse injection of hydrogen jets are reported. The computations are performed with the Ansys Fluent software package based on solving three-dimensional unsteady Reynolds-averaged Navier-Stokes equations with the $\kappa$-$\omega$ SST turbulence model and equations of detailed chemical kinetics of hydrogen combustion in air. The simulations predict self-ignition of the hydrogen-air mixture subsequently transforming to intense combustion with upstream motion of the flame from the ignition region. It is demonstrated that combustion occurs in thick subsonic regions, which merge at the channel axis in areas of elevated heat release, thus, forming a thermal throat. As a result, a system of normal shock waves is formed, which separate the boundary layer from the channel wall. The reverse flow transfers hot reaction products toward the step wall; thus, the thermal throat and shock waves are shifted upstream. As a result, the combustion wave and the shock wave enter the injector area, the “knocked-out” shock wave merge with the bow shock ahead of the jets, and thermal choking of the channel occurs.