Numerical study of a boundary layer bleedfor a rocket-based combined-cycle inlet in ejector mode

Fully integrated numerical simulations were performed for a ready-made central strut-based rocket-based combined-cycle (RBCC) engine operating in ejector mode, and the applicability of using a boundary layer bleed in the RBCC inlet designed for supersonic speeds was investigated in detail. The operational mechanism of the boundary layer bleed and its effects on the RBCC inlet and the engine under different off-design conditions in ejector mode were determined. The boundary layer bleed played different roles in the RBCC inlet for different flight regimes. When the RBCC engine took off, some air was entrained into the inlet through the bleed block, thereby inducing significant flow separation and a low-speed vortex, which deteriorated the inner flow and reduced the entraining air mass flow rate: thus, the total pressure loss increased and extra drag was exerted on the inlet. In the low subsonic regime, the bleed block had almost no impact on the RBCC engine and its inlet. However, as the RBCC engine accelerated into a high subsonic flight regime, the boundary layer bleed had a clearly positive effect, comprehensively improving the performance of the RBCC inlet. A boundary layer bleed operation strategy for the RBCC inlet in ejector mode was also developed in this study.