On the coupling effects of near-wall combustion and shock train in dual-mode scramjets

For the purpose of combustion enhancement and viscous drag reduction, fuel tends to be injected into the upstream of a scramjet's internal flow path, and the coupling of near-wall combustion and shock train may occur under this situation. This study numerically investigates the influence of combustion in turbulent boundary layers on shock train structures and pressure gradients. The numerical results reveal that the modification of the boundary layer structure and the reduction in skin friction caused by combustion in turbulent boundary layers are the intrinsic reasons for the decrease in shock train pressure gradient. In particular, within nearly the same length of shock train, combustion in turbulent boundary layers leads to a 20% reduction in the back pressure tolerance at an equivalence ratio of 0.1. Moreover, three representative one-dimensional (1D) shock train models are assessed under the condition of combustion in turbulent boundary layers. Among them, the 1D models established directly based on skin friction exhibits greater accuracy. Meanwhile, the Waltrup−Billig correlation based on momentum thickness is not applicable, further confirming the importance of including skin friction in shock train modeling.