Research On Characteristics Of Droplet Impacting And Oscillating On Wall

The wettability, which is expressed by the dynamic contact angle and the spread of the droplet, is the important factor influencing on the heat and mass transfer of the fluid. The researchers have done much work on the characteristics of the dynamic contact angle and spread of the droplet. However, there are many difficulties about the mathematical and theoretical research on the complexity of the interior droplet. Most of the literatures about the dynamic contact angle and the spread are experimental analysis and numerical simulation. The characteristics of the droplet are analyzed theoretically by building the model of the oscillating droplet in this article.Firstly, the droplet spreading and oscillating on the wall is simulated by the software FLUENT combined the user defined function (UDF) in this article. And the dynamic contact angle curved fitting of the experimental data is inputted continuously with the C language. The main research contents include the variation of the dynamic contact angle and the effects of dynamic contact angle on the oscillating of the spreading length and the height. The results show that the spreading length, height and dynamic contact angle are oscillated when the droplet is oscillating on the wall, and the maximum of the spreading length is achieved with the dynamic contact angle gets the maximum.Secondly, the droplet with different diameter, contact angle and spreading velocity impacting on the wall is simulated to research the characteristics of the oscillation and prove the correctly of the models. The results include the curve of the droplet spreading length oscillating on the wall and the relationships between the frequency, the attenuation coefficient and the maximum and stable value of the spreading length and height with the physical property and initial conditions. And the stable spreading length and height are influenced by nothing but the wettability of the wall. The frequency and maximum of the spreading length and height are contact with the surface tension. And the attenuation coefficient is affected by the viscosity of the fluid especially.Finally, three mathematical models of the oscillating droplet with different forces on the wall are built in this article, and the effects of the physical property and initial conditions of the droplet on the oscillating characteristics are researched in these models. The forces of oscillating droplet include the inertia force, surface tension, viscosity force and so on in these models. The results show that the spreading length of droplet is oscillating with constant amplitude in the ideal model without viscosity. In the two-dimensional model of droplet oscillating with viscosity, the spreading length reduces and the frequency rises with the increase of the surface tension, and the attenuation coefficient increasing with the growing of the viscosity. In the three-dimensional model, the results show that the static height of the oscillating droplet is associated with the wettability of the wall and the surface tension of the fluid. And the stable height is increasing with the growing of the surface tension when the wettability is decided. The models are proved correctly with the results of the experiment and numerical simulation.