LBM-LES Simulation Of Liquid Film Flow On The Pre-filming Surface Under High-speed Airflow

With the vigorous development of the aerospace industry,the problem of aviation pollution is becoming more and more serious,which directly affects the atmosphere and causes the greenhouse effect and global climate change.In order to reduce the energy consumption of aero-engines and achieve fuel economy,the development of aero-engine combustion chambers puts forward new requirements for the effect of fuel atomization and the quality of oil-gas mixture.During the atomization process of the pneumatic atomizing nozzle with pre-filming plate,the high-speed air flow drives the liquid film through the interface shear force and produce a wavy gas-liquid interface change.The liquid-gas mixing layer encountered in atomization owns a large density contrast,and the Reynolds number of gas happens to be much higher than that of liquid.Since the flow pattern of gas-liquid on the pre-filming surface directly affects the quality of liquid atomization at the lip of the pre-filming plate,it is of great significance to investigate the factors affecting the liquid film flow morphology in the later study of the liquid film breaking mechanism.For the analysis of the flow pattern of the liquid film on the pre-filming surface in an aero engine,due to the complex topological deformation of the gas-liquid interface under the sheer of high speed air flow,and there happens to be the higher density ratio in the gas-liquid layer,existing numerical simulation methods are more difficult to deal with related issues.In this paper,the lattice Boltzmann method(LBM)is selected to track the morphological changes of the gas-liquid interface,the main works are listed as follows:(1)According to the difficulties of the problem to be studied,the classic turbulence numerical simulation method large eddy simulation was selected and introduced it into LBM.Then the two methods of LBM and LBM-LES were used to simulate the lid-driven cavity flow and the backward-facing step flow,respectively,to verify the feasibility and superiority of LBM-LES application in single-phase turbulence.On this basis,the lattice Boltzmann model based on the phase field theory proposed by Liang et al.which specifically deals with the higher density ratio problem and introduces an additional interface force to eliminate the incompressible condition of the system that cannot be satisfied due to the density changes,thereby improving the accuracy of the model after modified.And the large-eddy simulation was introduced into the two-phase flow model again,so as to complete the calculation of the liquid film flow morphology model in this paper.Afterwards,this paper selects two problems that focus on the change of the gas-liquid interface in the gas-liquid two-phase flow: static droplets and Rayleigh-Taylor instability,to verify the capture accuracy of this model.(2)Furthermore,the liquid film flowing pattern on the pre-filming surface under the drive of airflow was investigated in this paper.The changes of liquid film flow morphology under different gas velocities,gas-liquid velocity ratios,gas-liquid density ratios,surface tensions and liquid film thicknesses were also investigated,and at last summarizes some conclusions,which does a good job of research reserving for the problem of liquid film breaking in the later period.The calculation results in this paper show that: LBM-LES has the higher numerical accuracy and stability when calculating high Reynolds number fluid flow.The modified two-phase flow phase field model can accurately track the morphological changes of the gas-liquid interface with the large density ratio.The difference of gas-liquid shear velocity induces the Kelvin-Helmholtz instability phenomenon at the two-phase interface,so the wave-shaped change will occur at the gas-liquid interface.Gas-liquid velocity ratio,density ratio,liquid film surface tension and liquid film thickness are all important indicators that affect the flow pattern of liquid film.