Unsteady regimes of hydrogen ignition and flame stabilization in a channel

Results of numerical simulations of reacting turbulent flows in a channel with a rectangular cross section and sudden expansion (backward-facing step) are reported. The simulations are performed for test conditions in a high-enthalpy hotshot wind tunnel with the Mach number at the channel entrance $\mathrm{M}=3.85$. Hydrogen is used as a fuel; it is injected transversely to the main flow ahead of the step from the upper and lower walls of the channel. The computations are performed in an unsteady three-dimensional formulation with the use of the Fluent 2020R1 software with reactions of hydrogen combustion in air being ignored or taken into account. The structure of reacting turbulent flows is studied; the flow parameters at different stages of the unsteady process of ignition and flame stabilization are determined. The computed data are compared with the results of an experiment in which the static pressure distribution over the channel walls were measured. It is demonstrated that the simulations correctly predict the unsteady pattern of ignition and flame propagation along the channel.