Numerical Simulation On Millimeter Water Droplet Deformation And Rupture By Nanosecond Laser-Pulse Impact

Droplet fragmentation is a common natural phenomenon and has a wide range of industrial applications in lithography,aerospace,and biomedical fields.It is shown that the velocity distribution generated by the pulse within the droplet is an important factor affecting the droplet deformation fragmentation,and little research has been reported on this velocity distribution.In this paper,the kinetic processes of millimeter droplets under nanosecond pulsed laser impact are investigated by numerical simulation.The mechanism of the different velocity distributions formed within the droplet during the laser-induced phase transition of the surface layer of the droplet on its deformation fragmentation are analyzed.Based on the Navier-Stokes equations,a hydrodynamic model of the laser-droplet interaction is established.And the evolution process of the droplet shape is simulated using the finite volume method.In the validation model,the evolution process of the droplet shape agrees well with the reported theoretical and experimental results,which proves the reliability of the model established in this paper.The influence of the velocity field formed by laser impact on droplet deformation and advancement under different energy is studied.The results show that when the Weber number is low,the droplet does not break as a whole when advancing,but shrinks under the action of surface tension.When the Weber number is higher,the droplet deforms more violently and even breaks.And the higher the Weber number is,the smaller the droplets break.Meanwhile,the dependence of droplet deformation parameters on Weber number was obtained by using Rayleigh-Taylor instability analysis.The effects of different laser energy distributions on droplet deformation were investigated.The results show that a uniform laser impact leads to the deformation of the droplet into a flat,thin sheet.Under the focused laser impact,it leads to the droplet deformation into curved thin film.In addition,vortex volume is generated during the droplet deformation and fragmentation.The vortex volume affects the process of droplet deformation fragmentation,causing the fine droplet fragments to spin,fuse,and break.The results of this paper can provide a basis for the relevant parameters in the deformation and fragmentation process of laser-impacted droplets,and are of reference value for laserinduced plasma light sources,laser-induced breakdown spectroscopy,and laser propulsion.