Effect of the wave structure of the flow in a supersonic combustor on ignition and flame stabilization

Results of numerical and experimental investigations of a high-velocity flow in a plane channel with sudden expansion in the form of a backward-facing step, which is used for flame stabilization in a supersonic flow, are presented. The experiments are performed in the IT-302M high-enthalpy short-duration wind tunnel under the following test conditions: Mach number at the combustor entrance $2.8$, Reynolds number $30\cdot10^6$ m$^{-1}$, and total temperature $T_0=2000$ K, i.e., close to flight conditions at $\mathrm{M}=6$. The numerical simulations are performed by solving full unsteady Reynolds-averaged Navier–Stokes equations supplemented with the $k$–$\omega$ SST turbulence model and a system of chemical kinetics including $38$ forward and backward reactions of combustion of a hydrogen-air mixture. Three configurations of the backward-facing step are considered: straight step without preliminary actions on the flow, with preliminary compression, and with preliminary expansion of the flow. It is demonstrated that the backward-facing step configuration exerts a significant effect on the separation region size, pressure distribution, and temperature in the channel behind the step, which are the parameters determining self-ignition of the mixture. The computed results show that preliminary compression of the flow creates conditions for effective ignition of the mixture. As a result, it is possible to obtain ignition of a prepared hydrogen-air mixture and its stable combustion over the entire channel height.