LAUSR

Abstract Droplet impinging on a flowing liquid film is investigated both experimentally and numerically in this study. Emphasis is placed on the interfacial evolution and dynamic feature as well as the corresponding underlying mechanisms behind. Results indicate that demarcation between splashing and non-splashing regimes can be expressed by a linear relationship between droplet Weber number and film flow Reynolds number, and a correlation estimating splashing threshold with mean absolute error of less than 2% is built up. While for the interface dynamic feature, increasing film flow rate leads to an asymmetrical interfacial evolution. In particular to the splashing at the higher film flow rates, it preferably takes place in the upstream position, but significantly suppressed in the downstream. Despite the very weak dependence of crown radial dimensions on impact velocity, the crown radiuses in the downstream are larger than those in the upstream due mainly to film shear force and streamwise migration, especially under high impact velocities. The crown top radius is reduced with increasing film flow rate as more liquid mass getting into the crown wall, but for the crown bottom radius, its effect is negligible. Increasing impact velocity leads to the increasing of crown both upstream and downstream heights, and the value in the upstream is much larger than the downstream, mainly caused by different intensities of flow kinematic discontinuity inside a liquid film. This asymmetry is aggravated further with increasing the film flow rate.