Study On Dynamic Contact Angle Of Droplet Oscillation

The droplet oscillation after droplet impact on the solid flat is one of a common phenomenon in solid-liquid two-phase flow,and it is also widely used in production and life.Such as,droplet movement on fiber,pesticide spraying with electric rotary table sprayer,application of ion plasma coating technology,and fuel spray impact process.The study on the phenomenon of droplets impacting on walls provides a theoretical basis for solving practical application problems.In this paper,the VOF model of Fluent software is used to conduct numerical simulation on the phenomenon of droplet impact on a solid wall,the droplet images in the simulation process are processed,and the method to obtain the droplet contact angle is determined by controlling variables.The influence of initial parameters(contact angle,the size of droplet,initial velocity)of droplet on dynamic contact angle is obtained by studying the dynamic contact angle.The influence of shear stress on morphology of droplet and dynamic contact angle is analyzed by changing the wall boundary condition.By assuming that the shape of droplet oscillating on the smooth flat is spherical,the theoretical spherical droplet oscillation model is established,and the differential equation of spherical droplet oscillation is derived through force analysis.In this paper,the former theoretical results of spherical droplet un-damped oscillation are modified by changing the initial parameters of droplet.The fourth-order Runge-Kutta method is used to solve the equation by using VS2010 software,so as to obtain the numerical solution of droplet spreading radius.Detailed theoretical results of equilibrium radius,amplitude,and average oscillation period are compared with those of the simulation.It can been found that deviations are not too large.Furthermore,the theoretical model is used to predict the effects of droplet various parameters on the spreading radius,the amplitude and the oscillation period.Based on the theoretical un-damped droplet oscillation model,the damped droplet oscillation model is analyzed in this paper.By comparing the theoretical and simulation results of droplet spreading radius,it can be seen that the theoretical equilibrium radius is larger than the simulation results.On the premise that the initial radius is the same,the deviation between equilibrium radii of the theoretical solutions are not more than 0.65% and the deviations between equilibrium radii of the numerical solutions are not more than 3.35%.Three shear stress formulas are used to study the effects of them on droplets oscillation.It can be found that the amplitude of spreading radius decreases with the increase of shear stress.The decay speed of spreading velocity increases with the shear stress increasing.It would beeffective to use the theory presented here to understand the processes of droplet impacting on the smooth horizontal solid surface.