Direct Numerical Simulation Of Primary Breakup In A Liquid Jet

In order to investigate the interfacial instability mechanism and primary atomization of a liquid jet,direct numerical simulations using VOF(Volume of Fluid)interface method and bounded compression scheme have been carried to model the interface evolution between liquid phase and air phase,with large-scale computing grid.Firstly,two low-speed liquid circular jets,which enter the static air at the speeds of 0.415m/s and 1.04m/s,are modeled.The development of a low-speed jet interface is divided into the jet formation stage,the liquid core growth stage,and the jet stability stage.The dynamic characteristics of a jet breakup in the above three stages are investigated.The calculated mean jet breakup length is close to empirical value.These confirm the high reliability and high accuracy of interface flow simulation used in this thesis.Afterwards,simulation of fuel liquid jet into still air at a speed of 30m/s is studied in terms of the dynamic characteristics.The deformation of jet tip and jet core,and the liquid-gas aerodynamic interaction,are also analyzed.Impacted against the quiescent gas,the liquid jet head atomizes into small ligaments and droplets with the aerodynamic effect,which makes the jet front an initial disturbed area.The perturbations are transferred to upstream through the jet core and ambient gas,therefore promoting further atomization.Along with the development of jet surface instability and atomization,the gas flow field becomes highly turbulent,which enhances the liquid-gas mixing.The dynamic mechanisms of liquid ligaments trigger from the liquid jet tip,deform by surrounding air,and pinch-off to produce droplets,are revealed.