Droplet impact on wetted structured surfaces

In this study, we numerically investigate the droplet impact onto a thin liquid film deposited on a structured surface with square pillars and cavities. The time evolution of crown geometry is strongly affected by the surface structure. When the thickness of the liquid film is larger than the structure height, the expanding speed of the crown base radius is independent of the structure width. However, if the liquid film thickness is equal to the structure height, the crown base expands slower as the structure width increases. Surface structures have strong effects on the crown height and radius, and can prevent ejected filament from breaking into satellite droplets for certain cases. For the liquid film with the thickness equal to the pillar height, both the crown height and the radius exhibit non-monotonic behaviors as the pillar width increases. There exists one pillar width which produces the smallest crown height and the largest crown radius.