Investigation On Cavity-induced Mixing Enhancement Mechanism Under Strong Shock Interference

In a scramjet combustion chamber,the residence time of airflow from the apture section to the outlet section is only milliseconds,and a flame stabilizer must be equipped to stabilize the flame.As an efficient and low resistance flame stabilizer suitable for supersonic flow,the cavity can achieve continuous and efficient combustion.However,the mixing enhancement mechanism of the cavity under the interference of a strong shock wave is still unclear.Taking the scramjet combustor as the research object,this paper establishes the mixing enhancement model based on the cavity and uses the numerical simulation method to deeply explore the mixing enhancement mechanism induced by the cavity under the interference of the strong shock wave.The specific research contents are as follows:Firstly,the Reynolds averaged N-S equation,SST k-ω turbulence model,and finite-rate laminar flow model used in this paper are introduced.The numerical method is validated using experimental data from the open literature.The comparison of the numerically simulated wall pressure distribution with the experimental data proves the accuracy of the numerical method.Then,the mixing characteristics of the cavity and groove flow field in supersonic flow are carried out to explore the mixing enhancement mechanism of groove structure.The flow structure of the inclined jet flow field is analyzed,and the performance parameters of the inclined jet flow field,such as circulation,mixing efficiency,and total pressure loss,are compared.Then,the enhancement characteristics of cavity-induced mixing under strong shock interference are studied.The main research factors are the ramp angle and the jet-to-crossflow pressure ratio.The complex shock structure and vortex structure formed by the interaction between the jet and oblique shock wave is analyzed.It is shown that there is an appropriate ramp angle to optimize the mixing efficiency.Further,the mixed fuel injection strategy induced by the cavity under strong shock interference is studied.The effects of injection angle and the number of injection holes on the flow field performance of the ethylene jet are mainly investigated.The numerical analysis shows that the ethylene jet with reverse injection has the best mixing performance.The mixing efficiency of double-hole injection is much higher than that of single-hole injection,and the mixing process can be completed in advance.Finally,the coupling characteristics of the cavity and the pulsed jet under strong shock interference are investigated,so as to further enhance the mixing of the supersonic flow and fuel.The results show that the pulsed jet with appropriate frequency can simultaneously achieve greater penetration depth and better mixing efficiency.It is revealed that the vortex structure induced by pulsed jet is beneficial to enhance the fuel mixing performance.To sum up,this study clarifies the mechanism of cavity-induced mixing enhancement under strong shock interference and adopts cavity and groove series mixing enhancement device,incident shock mixing enhancement and pulsed jet to promote the mixing process of the combustion chamber.The results mainly indicate that the mixer based on cavity configuration,ramp structure and pulsed jet can enhance the mixing performance of the fuel jet.