Impingement of a water droplet onto a water film on the surface with micro-structures

In the present study, we carried out an experimental investigation of the impacting process of a water droplet onto a water film on the surface with micro-structures. A parameter study of the droplet Weber number, the dimensionless water film thickness, and the dimensionless distance between two micro-protrusions was carefully performed. In addition, the impacting process of a water droplet onto a water film on the flat surface was also measured for comparisons. The results showed that, within the scope of this study, the increase of the dimen-sionless distance between two protrusions had a minor effect on the crown top diameter evolution and the crown lifetime. In addition, the number of secondary droplets was not monotonously affected by the increase of the dimensionless distance between two protrusions. Under the same droplet Weber number condition, when the water film was relatively thin, the dimensionless distance between two protrusions was found to have apparent influence on the evolution of crown base diameter. Besides, considering the effect of the dimensionless distance between two protrusions, we proposed a modified energy loss factor as well as two correlations for the maximum dimensionless crown height and the time to reach the maximum height.