Numerical study on the influence of plug nozzle expansion ratio on RBCC engine performance in ejector mode

In order to overcome the difficulty of enhancing the thrust of the rocket-based combined-cycle (RBCC) engine in ejector mode, improved configurations based on plug nozzle rocket ejectors were proposed, which were based on a center strut-based RBCC engine. Four RBCC configurations were numerically investigated under different flight Mach numbers and heights through CFD simulation for the whole flow path. It was found that the thrust of RBCC engines in the trajectory of ejector mode could be improved by 6.28–38.91 % after the introduction of the plug nozzle. The effects of a Laval nozzle rocket ejector and plug nozzle rocket ejectors with different expansion ratios on the performance of the RBCC engine are studied. The results show that the plug nozzle can improve the thrust of the rocket ejector. The introduction of the plug nozzle can move the thermal throat of the RBCC engine backward, reduce the blockage ratio, increase the air entraining, and finally improve the thrust augmentation of the RBCC engine. A plug nozzle rocket ejector configuration with its plume fully expanded is more conducive to improving the overall performance of the RBCC engine.