SPH Direct Numerical Calculation For The Problem Of Droplet Colliding Wet Surface: Energy Dissipation Analysis Of The Droplet

The impact of droplets on the wet wall is a common phenomenon of fluid flow in nature and industry.It has great significance to study the energy change after the droplet impact on the wet wall(liquid film)for ink jet printing and engine fuel atomization.In this paper,smoothed particle hydrodynamics(SPH)direct numerical calculation method is used to study droplet collision liquid membrane problem.The calculation results of liquid crown height after droplet impact on liquid film are compared with experimental results,which verifies the correctness of the calculation method.The energy dissipation process of droplet after collision is mainly analyzed,and the phenomenon of uneven printing and the phenomenon of ink-jet lump in ink-jet printing are explained.Firstly,in this paper,the SPH direct numerical method is used to simulate the liquid droplet impact liquid film phenomenon,and the changes of liquid height of crown is analyzed.The calculation results agree well with the experimental results,which successfully verify the correctness of this method.Then,the internal pressure changes of the liquid droplets and the liquid film are analyzed after the liquid droplets collided with the liquid film.At the beginning of the collision,the pressure is the main reason of promoting the formation and growth of the liquid crown.After the collision,the larger pressure difference is mainly distributed in the bottom of the liquid film.Secondly,the process of internal pressure change,the expansion of diameter variation,the axial momentum change and the kinetic energy change after the droplet impact dry wall and the droplet impact wet wall is analyzed.The energy dissipation process of droplet after droplet collision liquid film is summed up.After the droplets collide with the liquid film,the energy of the droplet is first concentrated in the neck region of the collision.After that,most of the kinetic energy is converted to the pressure energy of the droplet,and some of the energy is transferred to the liquid film and converted to the kinetic energy and the pressure energy of the liquid film.The pressure difference between the liquid droplet and the liquid film causes the droplet to overcome the influence of the surface tension of the liquid film,forming a thin jet above the liquid film,and then forming a liquid crown.When the droplet collide with the liquid film,the partial kinetic energy is affected by the viscous dissipation force of the liquid film,which makes the expansion diameter of the droplet and the expansion rate of the droplet is relatively small,and at the same time,which also makes the axialmomentum of the droplet is relatively small.Finally,the printing inhomogeneity and ink-jet block phenomenon in the ink-jet printing process are explained by the calculation results of the model in this paper.