Experimental investigation of cold ejecting characteristics and primary-secondary flow interaction in a strut-jet RBCC flowpath

Based on a typical strut-jet Rocket-Based Combined Cycle (RBCC) engine’s characteristic flow channel model, extensive cold jet entrainment experiments were carried out over a broad range of conditions, involving different ejector inlet configurations and strut-jet configurations. The study has provided an understanding of the entrainment air intake characteristics, as well as the interaction features and patterns between the primary and secondary flows. The research findings indicate that as the mass rate of primary flow and total pressure ratio increase, the Mach number of the secondary flow gradually increases, and the flow rate increases to a certain maximum value, while the entrainment ratio continues to decrease monotonically. Dimensional analysis shows that increasing the contraction ratio and contraction angle of the ejector inlet configuration can enhance the entrainment capability of the primary flow at low total pressure ratios, but the impact is smaller at high total pressure ratios. The strut-jet configuration with a single rectangular nozzle has a stronger entrainment capability compared to the configuration with a double circular nozzle. It can increase the mass flux ratio by 10% to 40% under the same mass rate of primary flow and nozzle throat area, and the structure with a wavy groove at the trailing edge of the strut is conducive to enhancing the entrainment capability. As the total pressure ratio between the primary and secondary flows increases, the velocity ratio and convective Mach number show a decreasing trend, while the static pressure ratio and density ratio increase. Ejector inlet configurations with a larger contraction ratio and double circular nozzle configurations lead to higher velocity ratios and convective Mach numbers, but lower static pressure and density ratios. These variations in parameter gradients determine the primary-secondary flow interaction processes and characteristics from the initial state perspective.