In this paper, a single-component multiphase pseudo-potential lattice Boltzmann model is developed to study droplet impact onto a thin liquid film in 2D coordinates. The model has certain capabilities which make it applicable to cases with large density ratios as high as 1000, low viscosities, and tunable values of surface tension independent of the density ratio. The coexistence values (densities) from the numerical model are compared to those of the analytical solution of the Maxwell construction. For further validation of the model, the simulation results for pressure difference at the droplet interface for various radii are compared to those of the theoretical solution based on the Laplace law. A test on an oscillating droplet is also performed for two different surface tension values to evaluate the ability of the model in simulating dynamic cases such as droplet impact. Next, the model is used to study a droplet impact onto a thin liquid film. It was found that the propagation rate of non-dimensional crown radius obeys the power law reported in the literature. Finally, effects of the surface tension (characterized as Weber number), the gas kinematic viscosity and the density ratio of liquid to gas on a droplet impact onto a thin liquid film are investigated. Results show that increasing the Weber number leads to more crown height causing more instability of the rim, and eventually generation of satellite droplets from the crown tip. Results of changing the gas kinematic viscosity revealed that at high density ratios such as 1000 selected in this paper, when the kinematic viscosity ratio of the gas to liquid is high (above 150), no satellite droplets are produced during the considered time. For a case with a low density ratio of 10, the raised liquid from the surface is not permitted to move freely in radial and vertical directions leading to the formation of an inward liquid turn on top of the raised liquid sheet. Therefore, the crown-shape liquid rise formed at high density ratios is not observed in a case of low density ratio.

Keywords