Thermodynamic performance modeling, optimization and numerical simulation of RBCC ejector mode

Ejector mode is a unique and critical phase of wide-range rocket-based combined cycle (RBCC) engine. In this paper, a quasi-one-dimensional thermodynamic performance modeling method, with more detailed model treatments for the inlet-diffuser system, primary/secondary flow interaction, and pressure feedback matching, was developed for operating characteristics studies and multi-objective optimization analysis of the ejector mode of an actual RBCC engine. A series of three-dimensional simulations of separate inlet and full flowpath was completed to validate the modeling study and provide further insight into the operating characteristics. The primary/secondary equilibrium pressure ratio functions a significant effect on ejector mode performance, a higher performance augmentation can be obtained by lower rocket pressure ratio, larger mixing section area ratio, smaller throttling throat and higher equivalence ratio, within an appropriate range. The positive performance augmentation can be realized at low flight Mach conditions, the coordination and trade-off relationships between specific impulse, performance augmentation ratio and thrust-to-area ratio during ejector mode are present by the Pareto-front from MOP analysis. It is further verified by CFD simulation that, the operating back-pressure at the exit of inlet-diffuser system functions a decisive influence on the airbreathing characteristics, the pressure feedback and matching should be well-controlled for secondary flowrate and performance augmentation. The thermodynamic modeling analysis results are basically consistent with those of numerical simulation, to validate the rationality and effectiveness of the modeling method.