Large-eddy simulation of shock-cooling-film interaction at helium and hydrogen injection

Laminar helium and hydrogen films at a Mach number 1.3 are injected through a slot into a fully turbulent freestream air flow at a Mach number 2.44. To numerically study by large-eddy simulations the impact of an impinging shock on various cooling films, first, reference solutions without shock impingement are computed and then, the helium and hydrogen cooling films interacting with an oblique shock at a pressure ratio of p3/p1 = 2.5 are analyzed. The comparison of the helium and hydrogen injections without shock shows the hydrogen injection to have a 1.14-fold better cooling effectiveness at 60% of the blowing rate of the helium injection. The shock-cooling-film interaction causes a massive separation bubble that is 23% larger at the hydrogen than at the helium injection. Nevertheless, the shock influenced cooling effectiveness at the hydrogen injection is only 30% reduced compared to a 40% decrease at the helium injection 100 slot heights downstream of the injection. The intense mixing in the shock-cooling-film interaction region shows a more rapid reduction of the helium and hydrogen mass fractions than in the zero-pressure gradient reference configurations. Overall, the cooling effectiveness of the hydrogen film is superior to that of the helium film independent from the streamwise pressure gradient.