Active and passive drag reduction methods for supersonic internal flow paths in combined cycle engines

Rocket-based combined cycle engines are the hotspots in the field of hypersonic combined power systems around the world. However, the significant internal flow path friction loss of the engine under supersonic inlet flow conditions severely limits further improvement of engine performance. The methods of grooves and gas film are proposed to reduce friction in the internal flow path of the engine. Numerical simulations based on Large Eddy Simulation are applied to obtain friction characteristics in the flow path under different Mach numbers and equivalence ratios. Results demonstrate that the friction-to-pressure drag ratio increases with Mach number and decreases with higher equivalence ratios. Moreover, the drag reduction mechanisms of grooves and gas films are analyzed. Through research on the shape and arrangement direction of grooves for drag reduction effects, it is found that transverse square grooves have better drag reduction characteristics, effectively reducing global drag by 8.15 %. Through the study on film drag reduction characteristics of methane/ethylene fuel, it is found that with a mixture ratio of 2:3, friction resistance on the upper wall surface is reduced by up to 10.29 %. A reduction in fuel injection temperature to 300 K results in a decrease in friction resistance by up to 11.79 %.