Experimental And Numerical Study Of Droplets Impacting On The Solid Surface

In this paper,experiments and numerical simulations were carried out on the process of droplets(water,ethanol and glycerol solution with different mass fractions)impacting on the solid surface.By changing the impact velocity of the droplets and the velocity of the solid surface,the effects of droplet viscosity,surface tension coefficient,impact velocity and surface motion velocity on the spreading diameter,spreading speed and spreading area after droplet impact were studied.Energy analysis method was used to analyze the surface energy,kinetic energy and energy dissipated in the viscosity during the impact process.Finally,the numerical simulation method was used to study the process of droplets impacting on the solid surface.The velocity field and pressure field inside the droplet were analyzed,and the numerical simulation and experimental results were compared.In the process of droplet impact,the general tendency of the droplet's spreading diameter and spreading area is to increase first and then decrease.Then spreading and retraction occur repeatedly until droplets reach equilibrium.As the viscosity and surface tension coefficient of the droplets decrease and the impact velocity increases,the spreading diameter and spreading area of the droplets increase.During the spreading process after the droplet impacting on the stationary solid surface,the spreading line speed of the droplet first increases to a maximum value in a short time and then gradually decreases to zero.When the droplet is retracting,the spreading line has a velocity opposite to that of the spreading process.As the droplet viscosity decreases,the surface tension coefficient increases,and the impact velocity increases,the retracting speed of the droplet spreading line increases.After the droplet impacts on the moving solid surface,the droplet will exhibit asymmetric spreading.The variation of the maximum spreading diameter and the spreading area of the droplet during the impact can be described by an empirical correlation with the Reynolds number and the Weber number.When the energy analysis method was used to analyze the surface energy,kinetic energy and energy dissipated in the viscosity of the droplet,it was found that the surface energy,kinetic energy and energy dissipated in the viscosity of the droplet are transformed into each other.The most influential factors for these energies are the viscosity of the droplet,the surface tension coefficient,and the impact velocity.The Mass-Spring-Damping model that can be used to predict the spreading properties of droplets during the impact process was optimized.It is not appropriate to use a static contact angle model when numerically simulating the process of droplet impact on a solid surface using the VOF(Volume of Fluid)method.The internal pressure difference after the droplet impacting on the solid surface is the cause of the droplet spreading,retraction,etc.The combination of the internal pressure difference and the surface tension and viscous force of the droplet determines the behavior and process characteristics of the droplet's spreading diameter and spreading speed.