Numerical Simulation Of Deposition And Splashing Of A Shear-thinning Droplet On Randomly Rough Surfaces

The droplet impact on the surface is a common physical phenomenon in natural and industrial production.It is widely used in the fields of energy,machinery,automobile coating and so on.Many scholars has studied the issue for many years due to the important guiding significance for the research of automobile surface coating.In this paper,a numerical model based on the phase field method was developed to characterize the deposition and splashing threshold of shear-thinning droplets on randomly rough surfaces.By resorting to specially designed simulation cases,the effects of geometrical properties of the surface on droplet impact dynamics were systematically revealed.In our works,under the same operating conditions,a numerical simulation of a shear-thinning droplet on smooth surface showed that a shear-thinning droplet can demonstrate quite different impact behavior as compared with a Newtonian droplet.We also discusses the evolution of the shear viscosity of internal droplet and the droplet morphological.The paper showed that even two surface have the same surface roughness,but have different morphology,The droplet initial spreading phase on ordered rough surface is great different with random rough surface.On randomly rough surfaces,the maximum spreading ratio increases with the increasing of either root-mean-square roughness(Rr)or Wenzel roughness parameter(Wr).With the same value of Wr,increasing Rr can lead to the decreasing of the final spreading ratio,and slight decreasing of equilibrium contact area and contact angle.With the same value of Rr,increasing Wr offers a faster deposition to reach an equilibrium state,and a linearly increased contact area.Increasing Rr can promote the droplet splashing,that is,the larger the surface roughness is,the smaller the critical We number for droplets to splash,droplets are easily splash.However,Wenzel roughness has no great influence on the droplet splashing.The splashing dynamics of droplets on surface is also related to Weber number,droplets would spread and reach equilibrium state on rough surface when We is low,droplet would break up during recoiling phase with higher We,when We is sufficient high,the droplet reaches the maximum state in spreading process will occur fingering splash.