Experimental study of primary-secondary flow ejecting and interaction characteristics in a RBCC flowpath with different inlet configuration

The Rocket-Based Combined-Cycle （RBCC） engine in ejector mode is dominated by the interaction between the primary rocket jet and secondary airflow. This interaction critically governs the ejector inlet characteristics and mode performance. Based on a typical strutjet-type RBCC flow-path model， a wide-range condition of cold flow ejector tests were conducted with four different inlet configurations， from the perspectives of geometric contraction and flow organization， the ejecting flow characteristics and the following primary-secondary flow interaction（PSFI） processes data were obtained. The research results indicate that， with the increasing primary mass flow rate and total pressure ratio， the secondary inflow Mach number and the mass flow rate gradually increase to a certain maximum value， while the bypass ratio shows a trend of initial increasing and then decreasing， for the experiments in this study， the primary-to-secondary total pressure ratio corresponding to the maximum entrainment ratio was approximately 2∶1， whereas the total pressure ratio associated with the maximum entrainment flow rate fell within the range of 9∶1 to 10∶1. A synergistic enhancement effect on the secondary flow ejecting capacity can be realized by appropriately increasing contraction ratio and contraction angle， but there is an upper limit of improvement. From the perspective of the PSFI internal flow processes， as the primary flow rate and total pressure ratio increase， the overall pressure distribution in the internal flow passage gradually decreases， while the Mach number distribution progressively rises. Concurrently， the downstream ejector pressure ratio exhibits an increasing trend， albeit accompanied by greater total pressure losses in both the primary and secondary flows. Under conditions of larger contraction ratios and contraction half-angles， the internal flow passage experiences lower pressure and higher Mach numbers. With the increasing primary-secondary flow total pressure ratio， the velocity ratio and convective Mach number show a decreasing trend， while the pressure ratio and density ratio gradually increases. The lower velocity ratio and convective Mach number are indicated with a larger inlet contraction ratio and contraction angle.