Numerical Simulation Method Of Supersonic Two-Phase Combustion Based On Flamelet Model

Scramjet,as power devices for high-speed vehicles,has received extensive attention from various countries in the world.It has important strategic significance in military strategy and the spacecraft field.In recent years,with the development of computer's software and hardware technology,numerical simulation has become an important way for the scramjet research.The flamelet model has been used in the numerical study of supersonic combustion by more and more researchers,due to its high computational efficiency and intuitive physical concept.On the other hand,liquid hydrocarbon fuels,which are commonly used in scramjet engines,have complicated flow problems in the combustion chamber,such as atomization,droplet movement,and coupling with the gas flow field.Based on these reasons,this paper takes the supersonic two-phase combustion based on the flamelet model as the research object,and studies the modeling and application of the flamelet model and the multi-scale problems of atomization under supersonic conditions.(1)Firstly,according to the basic idea of the flamelet,the relevant theories of the flamelet model and the FGM model based on the flamelet,are systematically introduced,and the corresponding laminar and turbulent database generation methods.And the wo models with compressible correction,were used in the numerical simulation of the scramjet flow field with strut or cavity,respectively,the feasibility and applicability of the flamelet model were verified.FGM model can capture the flame lift phenomenon,which make it more suitable for partial-premixed combustion It has been found that the shock wave,boundary layer and shear layer in the cavity affected each other strongly,which facilitates the introduction of the high temperature of the cavity into the main-stream and promotes combustion.(2)For the two-phase problem of atomization in the scramjet,an interface convection algorithm based on the VOF model was introduced to accurately capture the interface positions of the two phases.VOF model,LPT(Lagrangian Particle Tracking)model and the compressible modified K-H/R-T secondary break-up model were used respectively in the numerical study of the atomization process of liquid jet into cross flow(LJICF)under supersonic conditions.It has been found that VOF model is consistent with the experimental results in the near-field region of the injection,but the accuracy in the sparse phase region is low,while LPT model are the opposite.The penetration depth,droplet diameter,and spray spread distribution obtained by the compressible K-H/R-T model are superior to the original model.(3)The interface convection method(ICM)introduced in this paper can capture the two-phase interface efficiently and accurately.And a new multi-scale algorithm for simulating the atomization process has been proposed by coupling ICM with LPT method,and the water's LJICF was took as an example for verification.The results show that the multi-scale coupling algorithm proposed in this paper can accurately convert the VOF-descripted liquid phase in the sparse liquid zone into LPT particles.Numerical method can describe the multi-scale atomization process with the help of this multi-scale algorithm.The turbulence of the jet can increase the instability of the surface wave at the gas-liquid interface,allowing the droplets to be stripped from the liquid column earlier.(4)Using the flamelet model combined with LPT,numerical simulation of kerosene combustion in dual-cavity structure and strut/cavity structure under supersonic conditions was performed to verify the applicability of the flamelet model in supersonic two-phase combustion.It was found that the ignition delay caused by atomization and evaporation reduces the combustion and heat release in the main combustion zone.The swept strut cooperating with the downstream cavity can stabilize flame strongly.For the vertically arranged strut/cavity,the coupling effect of the high temperature backflow of the strut and of the cavity are weakened,with the increase of the distance between the two structures,which is not conducive to the formation of stable combustion.Through this research,the feasibility of the flamelet model used in the two-phase supersonic combustion and the two-phase coupling algorithm used in the multi-scale spray are demonstrated,which lays the foundation for the further study of the two-phase combustion process under supersonic conditions.