Effects of wall thermal state on shock wave/boundary layer interaction with foreign-gas supersonic film injection

Shock wave/boundary layer interaction (SWBLI) is considered to be one of the most complex physical phenomena in supersonic flowfield. The flow characteristics of SWBLI can be influenced by wall thermal state. However, in scramjet combustors, with supersonic film injected into the boundary layer, the effects of wall thermal state on SWBLI flow characteristics may have different characters. In this paper, the effects of wall thermal state on SWBLI with foreign-gas supersonic film injection are numerically investigated. During the numerical simulation, considering the actual application of scramjet engines, hydrogen and high-molecule gaseous hydrocarbon fueled supersonic film injections are taken into consideration. The results indicate that, either with or without supersonic film injection, wall thermal state changes both the wave structure and the flow characteristics. Furthermore, the interaction and separation length decrease with decreasing wall cooling heat flux. It is found that, the effects of wall thermal state on the interaction length are determined by its effects on the subsonic layer thickness. Moreover, decreased wall heat flux will cause momentum transport enhancement, which increases both near-wall momentum and wall shear stress, and consequently decreases the separation length. The interesting thing is that, foreign-gas injections lead to different relative variations of the interaction length and the separation length with wall thermal state. The effects of foreign-gas injections on the relative variations of the interaction length under different wall thermal states essentially depend on the foreign-gas specific heat capacity. Meanwhile, the relative variation of the separation length depends on the effects of foreign-gas injection on the relative density variation. It is worth mentioning that, due to the temperature range decrease caused by film injection, low-molecular hydrogen injection has significantly larger separation length relative variations compared with the situation without film injection and with hydrocarbon fuel injection. However, for high-molecular foreign-gas, the relative density variation depends on its own density change with temperature due to its high-density property.