Numerical Study Of Mixing Enhancement In Supersonic Transversal Jet

The resident time of fuel is very short in the scramjet combustor,therefore,the realization of fast and efficient fuel/air mixing has become a key technology for the development of scramjet engines.The strategy of wall fuel injection is to increase the fuel/air mixing efficiency by the complex large scale flow structure.It has been studied by many researchers due to the simplicity and efficiency of this technology.Based on the compressible flow solver in OpenFoam software,the enhancement of mixing efficiency of a supersonic transverse jet flow field in the passive and active modes is numerically investigated in the present research.The main works and conclusions are as follows.Based on the multi-stage transverse fuel injection strategy in supersonic flow,the simulations on the mixing process without combustion have been carried out,and the effects of fuel jet to cross-flow momentum flux ratios and injection angles on the mixing efficiency of the flow field are compared.The results show that the shock structure and the large-scale vortex structure of the convection jet flow field are enhanced compared with the single-hole jet,and the jet plume is bended due to the suppression of reflected shock.As the jet to cross-flow momentum flux ratio increases,the jet penetration is increased,however the mixing efficiency is decreased.The fuel injection angle affects the development the Counter-rotating Vortex Pairs(CVP).When the injection angle is 90°,the strength of the CVP reaches its maximum,which promotes the mixing of fuel/air.The results of pulse excitation on supersonic transverse jet mixing show that,compared with the steady-state jet,pulse excitation causes the jet plume to periodically fluctuate,and the maximum hydrogen mass fraction decay rate in the plume core region faster.There is an optimal value of the pulse frequency of 50kHz,which has the best effect of promoting fuel/air mixing.There is a lag in pulse transmission if the frequency is too low.However,the distance between neighbor vortex rings becomes shorter,and the penetration approaches a steady-state jet if the frequency is too high.As the pulse amplitude increases,the jet penetration and the mixing efficiency are increased.