Study Of Droplet Impact Dynamic Characteristics On Concave Surface

Droplet impingement is a very common phenomenon. Not only in nature everywhere, is it also widely used in mechanics, energy, metallurgy and other fields. Since it plays a key role in the operation efficiency of the related industrial equipment, it has led to the attention and research of many scholars for many years. Making a general survey of the past studies, the work of droplet impact on concave surface is insufficient, especially the impact along non-gravitational direction rarely appeared. Therefore, this paper uses both the experimental observation and numerical simulation methods to study the dynamic characteristics of droplet impact on concave surface.Dynamic processes of droplet impact on concave surface along the direction of gravity are experimental and numerical studied, mainly through the circumferential spreading coefficient and the horizontal spreading coefficient to investigate the deformation regulation of the whole droplet. The effect of the surface curvature on droplet spreading is discussed. It is found that the increase of curvature ratio hinders the droplet flow along the circumferential direction, and this effect decreases with the decrease of Weber number. Theoretical model and empirical formula of circumferential spreading coefficient are proposed based on experimental data. The influence of impact velocity, surface wettability and droplet properties on droplet deformation is studied. The results show that the Weber number mainly reflects the droplet impact energy. Droplet spreads and retracts on the smooth surface when the Weber number is small while it appears finger-type splash when the Weber number is large. Contact angle reflects the surface wettability. Droplet occurs the phenomenon of spreading and deposition when it impacts on the surface with a good wettability or small contact angle, while it rebounds when the surface has a bad wettability or large contact angle. The main forces acting on the droplet impact are the viscous force and the surface tension. It is difficult for droplet deformation when the viscosity is large, and the spreading phenomenon is also not obvious. The surface tension has little effect on the droplet spreading process, which promotes droplet retraction and aggregation..The three-dimensional numerical simulation method is applied for the study of droplet impact on concave surface perpendicular to the direction of gravity. It is found that the motion of droplet after impacting is mainly composed of a deformation motion and a longitudinal displacement movement. The effects of impact velocity, surface wettability, viscosity and surface tension on the motion of droplet are studied. The results show:for droplet deformation motion, longitudinal spreading length increases and spreading deformation intensifies when impact velocity increased. It promotes the droplet rebound when contact angle increased. The increase of viscosity hinders the spreading of droplet, while the surface tension promotes the droplet retraction. For droplet longitudinal displacement movement, impact velocity, surface wettability and surface tension have little effect on it, while the viscosity greatly affects it. A small viscosity means less viscous resistance, and the longitudinal displacement movement is close to the free falling movement. A large viscosity means more viscous resistance, so that the longitudinal displacement movement is a slow uniform movement.