Oscillation Characteristics of Single Droplet Impacting Vertically on Smooth Surfaces Using Volume of Fluid Method

The oscillation characteristics of a single droplet after normal collision with smooth surfaces are numerically investigated by using volume of fluid (VOF) method. An adaptive mesh refinement technique is used to guarantee the high computational accuracy of the interaction between the falling liquid droplet and the solid surface. The results of VOF simulations are consonant with the previously reported experiments. The effects of seven key issues on the oscillation characteristics of a liquid droplet advancing/recoiling onto both hydrophilic and hydrophobic surfaces are studied quantitatively with the help of dimensionless wetting length, average amplitude ratio and average oscillation period. These issues include impact velocity, contact angle, slip length, surface tension, droplet density, liquid viscosity and droplet diameter. Especially, surface and interface effects gradually become a primary factor that controls the droplet behavior as droplet size is reduced, and therefore the oscillation concerning micrometer-size droplet may be damped more rapidly. The presented study can contribute to provide more insight into the wetting kinetics of droplet collision, the interface interaction between the liquid droplet and the solid surface, and the oscillation features of the droplet spreading/receding after droplet impact.