Study On Dynamic Characteristics Of Moving Droplet Impacting Sessile Droplet

The phenomenon of droplet impact widely exists in nature,industry and agriculture,and life.Droplet impact dynamics has been widely concerned because of its wide application in engineering.In the practical application of droplets,the droplet impact phenomenon is more in the form of droplet impacting droplets.Compared with a droplet impacting a wall,when the moving droplet impacts a sessile droplet,the interaction between the two droplets will change the impact morphology and characteristics of the droplet,resulting in different characteristics of the moving droplet impacting the sessile droplet.Therefore,high-speed photography technology is used to systematically and deeply study the flow problem in the process of moving droplet impacting sessile droplets in this paper.(1)The process of different diameters of deionized water droplets impacting sessile droplets on the horizontal surface is studied,and the phenomena of complete rebound,partial rebound,compression deformation,coalescence are discussed.Furthermore,the We intervals for the rebound of droplets with different diameters are determined.And it was found that the increase of droplet diameter(increased Ohnesorge number)inhibited the droplet rebound.As the droplet diameter increases,the length of the We interval for droplet bounce decreases.(2)The interaction process of moving droplet impacting sessile droplet on the horizontal surface under different viscosity is studied.It is found that the full rebound phenomenon is produced at low We,and the liquid crown is produced at higher We.As the viscosity of the droplet increases,the We interval for droplet rebound increases,and the critical upper and lower limits of We for rebound are higher.And the dimensionless maximum rebound height decreases,the contact time increases,the maximum compression of the droplet decreases gradually,the deformation of the droplet becomes more severe,and the maximum liquid crown diameter gradually decreases.(3)The evolution process of moving droplet impacting sessile droplet on the concave surface is studied.It is found that the rebound will occur at a low We,and when the We of the impacting droplet exceeds the critical value of the droplet rebound,it will no longer rebound and coalesce directly with the sessile droplet.With the increase of the radius of curvature of the concave surface,the We interval of the droplet rebound,the upper limit of the critical We of the rebound,and the dimensionless maximum rebound height all show a trend of first increasing and then decreasing,the contact time decreases,and the maximum compression increases.The ratio of the dimensionless maximum horizontal diameter of the impacting droplet to the sessile droplet does not change with the We.Finally,through the comparison of the above studies,it can be concluded that the concave curved surface strengthens the rebound of the droplet,and the We interval and the critical We upper limit of the droplet rebound on the concave curved surface are larger than those on the horizontal surface.And the increase in viscosity facilitates the rebound of the droplet.As the viscosity of the droplet increases and the shape of the wall changes,partial rebound phenomenon no longer occurs.