Dynamics study of double droplets impacting liquid film based on phase-field lattice Boltzmann method

In this paper, we conduct a numerical study on the dynamics of double droplets impacting a liquid film using the phase-field lattice Boltzmann method. The effects of the solid surface roughness, Weber number, Reynolds number, the film thickness, the horizontal distance between the droplets and the density ratio have been investigated systematically. For the flat case (radius of cavity is zero), the droplets with high Weber and Reynolds numbers will lead to a marked increase in the maximum rise height. In addition, the horizontal distance between the droplets also has a significant influence on the dynamic process of the droplets. The maximum rise height first increases and then decreases, with increasing the horizontal distance between the droplets. Conversely, for the rough solid surface, there exists the following relationship between the crown root radius and time, r/(2R)≈α(Ut/(2R))0.25, where r denotes the crown root radius, R represents the initial droplet radius and U is the initial droplet velocity. The numerical results indicate that the effect of the solid surface roughness on the crown root radius is similar to that of a single droplet. Furthermore, we found that the film thickness is inversely proportional to the maximum rise height, which is different from the flat case.