Reduction of surface friction drag in Scramjet engine by boundary layer combustion

Abstract This study investigates the effects of boundary layer combustion on skin friction reduction in a model scramjet combustor. The 4-equation RANS model (Transition SST model) is employed as the turbulence model and one experimental case which involves supersonic turbulent boundary layer combustion is used for validating the numerical simulation method. Then a wall jet device which can be used to inject hydrogen into boundary layer is designed and added to the lower wall of the combustor in the model scramjet engine. The numerical results showed that the optimal ratio between the primary fuel, producing thrust, and the wall jet fuel, used for drag reduction, for getting the largest skin-friction drag reduction when installing the wall jet device in the combustor, is 3:1. The study of modifying the location of the wall jet device showed that setting the wall jet position too close to the upstream or downstream could not get the maximum overall drag reduction. The installation position in the flow path depends on the coupling of primary fuel and wall jet fuel combustion. In practical scramjet design, the distribution ratio of primary to wall jet fuel and the location of wall jet device should be weighed to improve skin-friction reduction efficiency and overall engine performance.