The results of a computational study of turbulent supersonic flows in a channel with a backward-facing step are presented, taking into account crossflow injection of argon and hydrogen jets. The calculations are performed at Mach number M = 4 at the channel entrance under the real flight conditions, which were realized in experiments in a hot-shot aerodynamic facility. The comparison of the flowfields is carried out for jet-to-freestream momentum ratio range J = 1 ÷ 6. It is shown that the degree of mixing, estimated from the uniformity index, increases with J increasing and with an increase in the molecular weight of the injected gas at the same J.