Large eddy simulation of shock-combustion-film interaction at hydrogen injection in a model scramjet combustor

Supersonic film cooling, which utilizes fuel onboard, is a promising method for protecting the wall of a scramjet combustor from intense heat and friction loads during high-speed flight. Large eddy simulation (LES) is conducted to study the coupled interactions among shock, combustion, and film. First, reference solutions for individual effects of shock and combustion on film performance are computed. Then the coupled effects are analyzed based on the reactive hydrogen film impinged by an oblique shock at a deflection angle of 2° The results show that the incident shock will enhance the transport processes after the impingement point by an increased turbulence production in the separation bubble. On the contrary, boundary layer combustion has the effect of constraining the transport processes in the mixing layer due to the low-density region caused by thermal expansion. This leads to a decrease in the mixing rate and wall friction. Although the heat flux transported to the film is also reduced by combustion, the wall temperature still increases due to the excessive compensation of heat from intense endothermic chemistry. Besides, the boundary layer combustion of hydrogen film exhibits self-limited characteristic since the mixing process is further delayed under combustion circumstance. Therefore, an incident shock will break the mixing bottleneck of the boundary layer combustion, leading to a more intense reaction with a more wrinkled flame front. The current findings indicate that the additional gaining of cooling and friction reduction performance is exclusive, but also point out the direction for simultaneous improvement of the two performances.