Numerical Simulation Of Droplet Impinging On Surface Under Electrical Field

Deformation of droplets under electric field is widespread in industrial applications,such as electrical injection,inkjet printing,fuel atomization,biomedicine,and transmission line icing.Having a deep physical insight of droplets in an electrical field will promote the design and optimization of various equipment.However,the electrical field and the flow field are strongly coupled processes.The droplets are controlled by inertial force,viscous force,surface tension and electrical filed force under electrical field,which makes their motion behavior very complicated.In this study,the VOF method is adopted to track the phase interface.At the same time,the dynamic contact angle is coupled to simulate the dynamic process of the droplet impacting the surface.The charge transport equation and Maxwell's stress equation are coupled to conduct the motion process of droplets impacting the surface under the action of electric field.The results obtained by using this model are compared verified with the visual experimental data and are in good agreement.The main research contents are as follows:(1)The coupled electrohydrodynamic solver is based on the Interfoam solver in the open source software Open FOAM platform.The electric field force acting on the droplet is added to the NS equation as a source term.At the same time,the conservative form of the charge equation is solved to couple the electric field and flow field.Coupled with a dynamic contact angle model,it can capture the details of physical phenomena more accurately and obtain accurate simulation results.The simulation results of the impact of the droplet on the surface is compared with the experiment to verify the correctness of the implement of the dynamic contact angle model.Through the comparison between the experiment of oil stretching and the impact of the droplet on the surface under electric field,which verifies the interaction between the electric field equation,the interface capturing method and the contact angle model.With this model,which can accurately simulate the dynamic process of droplets under the electric field.(2)The movement process of a single droplet impacting on the surface was simulated,and the effect of the dynamic contact angle model on the droplet impact process was studied.The effects of different contact angle models and contact angle hysteresis on the hydrophilic surface were compared.The effect of the receding angle on the secondary droplet separation after the droplet bounced back,and the effect of We number on the impact of the droplet on the hydrophilic surface was studied.(3)The dynamic process of the droplets impacting the hydrophilic surface and the superhydrophobic surface under the electric field is analyzed.The influence of the electric field intensity and We numbers on the movement behavior of the droplets impacting the hydrophilic surface and the superhydrophobic surface under the electric field is discussed.We focus on the changes in the amount of surface charge,electric field force,and the distortion of the electric field intensity during droplet impact.Research shows that the implement of the contact angle hysteresis in the dynamic contact angle model can more accurately capture the experimental details,such as the separation of secondary droplets.Increasing the advancing angle can inhibit the spreading of the droplets,and increasing the receding angle makes the droplets easier to oscillate.on the hydrophilic surface,as the We number increases,the spreading diameter of the droplet increases,the maximum stretching coefficient decreases,and on the superhydrophobic surface,As the We number increases,the spreading coefficient increases,the droplet's maximum stretching coefficient is greater,and the secondary droplets are more easily separated.For the droplet impact process under the action of an electric field,it was found that the morphological change of the droplet impact process will cause local distortion of the field strength at the top of the droplet.The Coulomb repulsion of the charge at a certain position on the surface is greater than the surface tension,and the ejection phenomenon occurs.The electric field intensity has a small effect on the spreading coefficient of the droplet,but has a greater effect on the stretching coefficient of the droplet.As the field strength increases,the maximum stretching height of the droplet increases.When the droplet is ejected,the stretching height increases sharply.At the same time,the electric field intensity,the amount of charge,and the electric field force on the droplet surface increase,which promotes the advancement of the secondary droplet splitting.However,due to droplet breakup and filament breakage,the overall electric field force on the droplet surface changes drastically,causing droplets to fall back,rise,and oscillate.The research results of this paper provide a reference for the mechanism research in the fields of electro wetting,inkjet printing and power line anti-icing.