Numerical Simulation Of Mixing And Combustion Process Of Transverse Spray In Supersonic Flows

The present study,focusing on the liquid fuel jet in the scramjet engine and aiming to simulate the complete process of injection,atomization,mixing,evaporation,and combustion of liquid fuel jet in the supersonic flow,established the large eddy simulation method for two-phase combustion and analyzed the basic physical processes and mechanisms involved in the mixing and combustion process of the transverse spray in supersonic flows.Firstly,based on the Eulerian-Lagrangian framework,a Large Eddy Simulation method suitable for two-phase flow in supersonic flow was established.The efficient management of droplets and the efficient tracking and localization of droplets under deformed mesh conditions were realized by the dynamic linked list based on the grid node.The trilinear interpolation and the source term statistical based on the nearest grid node were implemented for the two-way coupling of the gas phase and liquid phase.Based on domain decomposition and virtual mesh for droplet sharing,the large-scale parallel simulation of two-phase flow was further realized.The position and velocity of small droplets after a big droplet breakup were corrected by considering the deformation of the droplet.The above numerical models and methods were tested and verified for the atomization process of a transverse water jet in supersonic flow.The numerical simulation results successfully reproduced the experimental observation of the liquid trailing phenomenon and revealed the physical mechanism.The numerical simulation of a transverse liquid jet on a flat plate in supersonic flow was carried out and the three-dimensional mixing process was analyzed.The structure of the Counter-rotating Vortex Pair(CVP)was found to be different from the transverse gas jet and the transverse liquid jet in the subsonic flow.Based on the comparative analysis of the pressure gradient force and the source term of droplets,the formation mechanism of the CVP was revealed and the three-dimensional flow topology of the liquid transverse jet in supersonic flow was constructed.The atomization and mixing process of a liquid jet upstream of the cavity was numerically simulated.The interaction between the jet and the cavity,and the distribution and transport characteristics of the spray near the cavity were analyzed.The numerical simulation successfully captured the vortex structures in the jet boundary mixing layer which was also observed in the experiment.The temporal evolution of the droplet family was revealed,that is,the droplet family evolves from the backslash "\" type as shown in the liquid trailing phenomenon to the less "<" type,finally presents as a forward slash "/" type.The CVPs(Upper CVP and Wall CVP)upstream of the cavity have a significant effect on the entrainment behavior of the droplet into the cavity.The interaction between the jet and the cavity forms two obvious induced vortices inside the cavity.Based on the two-phase code containing the atomization model,the infinite thermal conductivity evaporation model was implemented and the numerical simulation of the evaporation process of the spray field was carried out and been verified.The numerical results of the liquid kerosene jet in the cavity-based combustor well revealed the evaporation characteristics of the liquid fuel jet in the high total temperature supersonic flow and clarified the ignition environment near the cavity.The droplets could hardly survive in the cavity,and only a small portion of the droplets are entrained into the upstream cavity.The injection pressure affects the total quantity of fuel entrained into the cavity by affecting the fuel distribution in the near-wall region and the total fuel mass flow rate.On the expected development path of the flame kernel,the mass fraction of the combustible fuel and the gas phase temperature increase gradually,while the turbulent kinetic energy decreases gradually,which is beneficial to the maintenance and development of the flame kernel.Based on a two-step chemical scheme and the Quasi-Laminar(QL)reaction rate model,the whole processes of the atomization,evaporation,and combustion of kerosene jet were simulated and been verified.A large-scale simulation was carried out for two typical combustion conditions in the experiment,and the basic characteristics of the gas phase and liquid phase under different combustion modes were analyzed.In the weak combustion mode,the interaction between the spray and the flame is weak,and the flame is mainly a premixed flame.In the strong combustion mode,the flame has strong instability characteristics,and the distribution characteristics of the fuel spray are greatly affected by the flame.In the process of reverse propagation,the flame gradually changes from premixed flame to diffused flame.In the upstream region of the jet,the flame is primarily a diffusion flame;in the far downstream region,the flame is mainly a premixed flame.