Investigation Of Over/Under TBCC Inlet Mode Transition Characteristics

To realize the property of self-launching, reusability, wide fight scope, fine low-speed performance, and high reliability, etc. combined cycle propulsion syst em is the best option. Turbine-based combined cycle engine combines turbojet and ramjet. For the over-under TBCC engine, these two engines work in independent duct, which lead to low interference and easy aerodynamic design and control. The mode transition of TBCC engine is the switch of turbojet and ramjet, which is also the highlight and difficulty of research. The mode transition process relies on the flow separation of inlet. Therefore, this thesis studied some key points of the mode transition process of over-under TBCC inlet, including the performance variation trend, the unstart feature of inlet, and the effects of transition Mach number.Firstly, with the combination of steady and unsteady numerical simulation, and assisted by mesh updating technique, the flow field of TBCC inlet, performance parameter of TBCC inlet, and the effects mode transition time was analyzed. The flow field of inlet was studied at non-pressure and high-pressure conditions. Then, the variation trend of flow mass rate coefficient, total pressure recovery, and outlet Mach number was showed. It was revealed that the propagation of shock wave lags behind the rotation of splitter, and the shorter the mode transition time, the more obvious the delay.Then, the unstart property of turbine inlet and ramjet inlet in the mode transition process was analyzed, and the influence of boundary layer suction on ramjet inlet unstart was discussed. Studies showed that in the process of mode transition, the ability of back pressure resistance of turbine inlet descends, and the inlet buzz didn’t happen. However, the ability of back pressure resistance of ramjet inlet ascends, and there exist inlet buzz. The suction improved the start performance of ramjet inlet at the end of mode transition.Finally, the effects of transition Mach number on inlet mode transition w ere studied. 3 Mach number was utilized to analyze the performance parameter and unstart characteristics of TBCC inlet. Overview, the increase of transition Mach number has little influence on the performance of inlet, but affects dramatically the ability of back pressure resistance of TBCC inlet.