Drag reduction characteristics of boundary layer combustion with hydrocarbon fueled discrete hole film injection

The hydrocarbon-fueled scramjet engine faces the challenge of extreme aerodynamic friction drag caused by the hypersonic inlet and high-intensity combustion. Using gaseous hydrocarbon-fueled discrete hole film boundary layer combustion effectively reduces friction drag in the internal flow and enhances drag reduction characteristics. Numerical simulations based on the RANS method compare the differences in boundary layer combustion drag reduction characteristics between discrete hole film injection and slot film injection and reveal the mechanisms of combustion drag reduction in cylindrical discrete hole film boundary layers. The results show that the combustion drag reduction of discrete hole film injection in the near-field flow is 5.3 % higher compared to slot film injection. The discrete hole film forms a complex counter-rotating vortex pair (CVP) structure through transverse jet interaction, which enhances the mixing process between the film jet and the main flow, thereby facilitating the combustion drag reduction effect. The blowing ratio influences regional changes in combustion drag reduction within the boundary layer of hydrocarbon fuels. Additionally, increasing the inclination angle of discrete hole film injection from 30° to 120° decreases wall shear stress by 26.78 % to 30.32 %, showing an opposite trend to the decrease in wall temperature. Furthermore, the effect of the discrete hole length-to-diameter ratio on the cylindrical hole film is primarily observed in the hydrocarbon fuel cracking region downstream of the discrete holes. An optimal length-to-diameter ratio L/D = 3 results in a 19.71 % decrease in combustion drag in the boundary layer.