Numerical investigation of skin-friction reduction in a supersonic channel

This paper reports on effects of different gases injected into boundary layer on the skin friction in a supersonic backward facing channel. Four gases, including hydrogen, methane, ethylene and helium, are studied via ANSYS FLUENT. The first three gases are burnt in the boundary layer, while helium is studied to identify the effect of density. These gases are respectively injected into the boundary layer on the upper and lower walls through an array of small portholes in a Mach 2.0 and a Mach 2.3 flow parallelly. Results show that the low density gas, hydrogen and helium have a positive effect on skin-friction reduction without combustion, while there is no significant change in skin friction with methane and ethylene injection. The three combustible gases have rather remarkable effect on drag reduction when burning in near wall region. Among them, hydrogen has the largest effect which can achieve 37.8% drag reduction. Moreover, due to the actuation of the rearward facing step and the confined space together, the skin friction shows a very interesting behavior along the channel path.