Investigation On Fuel Injection Strategy On Forebody/Inlet And Its Mixing Enhancement Mechanism In Hypersonic Flows

As one of the most promising propulsion systems of the air-breathing hypersonic vehicle,the shcramjet engine is a new concept engine.Injection on the forebody/inlet is one of the key technologies of the shcramjet.In this dissertation,numerical simulation is used to investigate the mixing effect and mixing enhancement mechanism of fuel injection on forebody/inlet in hypersonic flows.At first,the current research status on the shcramjet engine,the single injection,the dual injection and the pulsed injection is introduced systematically to make a clear thought for the following investigation.Then,based on the experimental data of the supersonic inlet and transverse injection in the supersonic flow published,the code validation and grid independence analysis are carried out.The results obtained show that three-dimensional RANS equations coupled with the SST k-ω turbulence model are suitable for this dissertation.The meshes with different scales have little influence on the results.Next,the injection angle and the jet-to-crossflow pressure ratio are taken into consideration,and the mixing efficiency,the total pressure loss,the fuel penetration depth and the mixing length are evaluated.The results show that both the injection angle and the jet-to-crossflow pressure ratio have an important influence on the flow fields.Subsequently,one air injector is mounted downstream of the hydrogen injector.The distance between two injectors and the formation of the recirculation zone are studied.The results show that the smaller the distance,the higher the mixing efficiency.The shear vortex is induced by the interaction between the inflow and the injection,resulting in the recirculaion zones and merging lots of air to accelerate the mixing process.Then,the sine wave pulsed injections with different periods are proposed and the mixing enhancement mechanism of the pulsed jet is revealed.The intermittment injection of the pulsed jet has distinctive advantage of reducing total pressure loss and improving fuel penetration depth.The mixing enhancement mechanism of the pulsed jet is not producing large scale vortex structures but focusing on merging a mass of air around into the fuel core by the intermittent injection to get a better mixing effect.At last,the typical standard and swept cantilevered ramp injectors are investigated,both with the formation of the shock wave system around the injector.The results show that the vortex induced by the velocity difference and the collision between different gas flows lead to the complex shock wave system.The mixing enhancement mechanism of the cantilevered ramp injection are shearing action in the near flow field and large scale vortex structures induced by the cantilevered ramp configuration in the far flow field.