In this paper, simultaneous impact of two parallel drops on a thin liquid film is investigated using the lattice Boltzmann method. The purpose of this study is to investigate the effects of surface tension (characterized by Weber number), distance between two drops, and gas kinematic viscosity on the impact. The developed numerical model in this paper which is based on the Shan and Chen pseudo-potential two-phase model makes it possible to access large density ratios, low viscosities, and tunable values of surface tension independent of the density ratio. The model is validated by comparing the coexistence densities with those of Maxwell analytical solution, evaluating the Laplace law for a droplet, and simulating single droplet impact on a thin liquid film. Simulation results of two drops simultaneous impact show that after impact, two jets raised between the drops join each other and form a central jet. Height of this jet increases with time leading to separation of secondary droplets from its tip. When the surface tension value is decreased, the central jet height is increased, but size of the separated droplets is reduced. The crown shape observed in single drop impact is also seen in simultaneous impact of two drops. Increasing distance between two drops leads to a smaller central jet height and an increase in the crown radius. The crown height, however, was found to be independent of the distance. Finally, increasing gas kinematic viscosity reduces the central jet rising speed and delays separation of secondary droplets from the jet.

Keywords: Lattice Boltzmann Method, Impact, Droplet, single component two-phase, Shan and Chen

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