Mechanism and contact time of off-center impacts at relatively high Weber numbers

Abstract

When a droplet off-center impacts a superhydrophobic surface with macro-ridges, it may split into two asymmetric fragments that then exhibit asymmetric spreading and retraction phenomena. The contact time depends on the volume of the larger fragment, which is determined by the off-center distance. However, it is difficult to predict the contact time in practical applications. To establish a quantitative law of the contact time based on the volume of the larger fragment, the dynamics of off-center impacts at relatively high Weber numbers are investigated using lattice Boltzmann method simulations. The relationship between the volume of the larger fragment and the off-center distance is established to elucidate the mechanism of the redistribution of liquid volume. On this basis, another mechanism, i.e., the asymmetry of the liquid film, is studied to derive the relationship between the contact time and the length of the larger liquid film. Combining the two mechanisms, a quantitative relationship of the contact time for off-center impacts, which is proved to be applied in a wide range of Weber numbers, is finally established.