Numerical study on characteristics of single droplet impacting on wetted surface

In this paper, the mathematical and physical models of the single droplet impacting on liquid film are established. The axisymmetric numerical simulation of the single droplet impacting on liquid film is carried out by using the Couple Level-set and VOF (Volume of Fluid) numerical simulation method, which is verified by experiment, studying the influence of the liquid film thickness, surface tension, viscosity, and density of liquid on the liquid crown, and analyzing the thickness effect on the neck ejecta sheet. Through the analysis of pressure and velocity field, the mechanism of crown formation is studied. The results show that: (1) experiment and simulation are in good agreement, so CLSVOF method (the Couple Level-set and VOF) is suitable for research of droplet impacting on liquid film; (2) with the increase of liquid film thickness, the expansion radius and height of crown decrease, and the crater depth increases; (3) the surface tension, density, and viscosity of the fluid have influence on the crown; (4) ejecta sheet velocity decreases with the increase of the liquid film thickness but when H^* > 1.0 (ratio of film thickness to droplet diameter), the ejecta sheet velocity does not change; (5) neck ejecta sheet is caused by neck pressure difference.