Experimental Study And Large Eddy Simulation Of Primary Breakup Of Liquid Jet In Supersonic Cross Flow

The primary breakup of liquid jet in supersonic crossflow was studied in this thesis.Experimental study and numerical simulation are involved in the research.The liquid breakup process in the supersonic crossflow was observed with the instantaneous images captured by optical methods.The atomization consists of liquid column breaking into liquid bump,liquid bump breaking into droplets and the secondary breakup of droplets.The surface waves were observed in the liquid column and bump breakup with the droplets stripped off by strong aerodynamic force.There were waves of different wave lengths on the windward side of the liquid jet along which the average wave length increased.The liquid jet breaks at the trough of the waves with the disturbance developing.The angle between liquid jet and supersonic flow and the pressure measured on the wall were taken as two quantitative indexes to study the influence of injection pressure,orifice diameter and total temperature of the gas flow.The analysis indicates that penetrability of the liquid jet was correlated positively with jet pressure and orifice diameter.The large eddy simulation combined with CLSVOF method was applied in this thesis.This numerical simulation mainly consisted of CLSVOF interface tracking method and two phase large eddy simulation in which compressible solver was coupled with incompressible solver.The CLSVOF combined the advantages of Level Set and Volume of Fluid so that the CLSVOF possessed the simplicity of Level Set and the mass conservation of VOF.The key to realize the two phase large eddy simulation was to treat the surface tension with ghost fluid method and utilize the divergence freed liquid velocity extrapolation to reduce the numerical breakup.The numerical method developed in the thesis was verified by simulating the droplet breakup in supersonic flow.Breakup modes and distributions were compared between the simulation results and experimental results.After the verification,the liquid jet breakup in supersonic crossflow was simulated in different We,Ma and liquid/gas momentum flux ratio when the standard condition was that Ma,We and liquid/gas momentum flux ratio equal 2.1,500 and 10 respectively.Conditions of different We is 100,300,500,700,900,1100.Similarly with droplet breakup the We number influenced the breakup modes of the liquid jet.And wave length was larger with bigger We.The surface wave along the jet can be explained by the Rayleigh-Taylor instability while the wave cross the jet was not controlled mainly by Rayleigh-Taylor instability through the comparation between theoretical and computational results.The analysis of liquid distribution and frequency characteristic indicated that We mainly controlled the instability on the liquid surface and breakup degree.Conditions of different liquid/gas momentum flux ratio were 5,10,15.The penetrability of the liquid jet was better with larger liquid/gas momentum flux ratio.The liquid/gas momentum flux ratio represented the momentum relation between liquid jet and supersonic flow.The analysis of liquid distribution and frequency characteristics showed that liquid/gas momentum flux ratio indicated mutual effects between liquid and gas.In other words,the ratio represented how intense the mutual action between liquid and gas.However Ma did not influence distribution and frequency characteristics of liquid jet as much as We and liquid/gas momentum flux ratio did.