Mechanism of double droplets off-center impact

Dynamics of double-droplet off-centered impact on a superhydrophobic substrate is investigated. The effects of the distance between droplets, off-centered distance as well as the Weber number on the impact dynamics are systematically investigated by lattice Boltzmann method simulations. For the off-centered impact of double droplets, two distinct regions are identified, i.e., the contact time increasing region (TIR) and the decreasing region (TDR). For TIR, the liquid film exhibits a “butterfly-like” shape during the spreading and then recoils toward the center, while for TDR, the liquid film presents a “rod-like” shape and then retracts toward the ends of the rod, leading a pancake bounce pattern. Considering the mechanism of the redistribution of liquid volume and the asymmetric of the liquid film, the quantitative expression of contact time for TIR is established. Based on this, the mechanism of the interaction between droplets is further studied to calibrate the expression of the contact time by introducing the center distance between droplets, which is certificated to be used in a large range of distances between droplets, off-centered distance, and the Weber number.