Numerical analysis and insight of drop impacting dynamics upon a liquid film

A single liquid drop impinging onto very thin spherical films was observed with the aid of a high-speed digital camera at frames per second. The liquid sheet produced at a high impact velocity was mainly concerned. Also more features and insights of the sheet were numerically studied using the coupled level set and volume of fluid method, considering effects of four non-dimensional parameters: Reynolds number, Weber number, dimensionless film thickness and drop-film curvature ratio. Results reveal that splashing can be suppressed by decreasing Reynolds number and Weber number. An increase in both the dimensionless film thickness and the film-drop curvature ratio is adverse to splashing onset. In addition, these four parameters can also greatly affect the geometrical shape and diameter of the sheet. In the second part, the air gap generated in the sheet-film contact neck region was investigated. It was noted that gas and liquid vortices produced near the liquid film surface render the film liquid to sink to form the air gap. Meanwhile, liquid accumulates inside the liquid sheet base gradually. Analysis in the velocity field suggests that the very thin preexisting film should be responsible for the vortex generation and the curvature ratio has minor effects on it, which is confirmed quantitatively as well.