An improved pseudopotential multi-relaxation-time Lattice Boltzmann model for binary droplets collision with large density ratio

This study aims to investigate the binary droplet collisions with large density ratios (DR) via an improved pseudopotential multiple-relaxation-time (MRT) Lattice Boltzmann Method (LBM) model. This model satisfies the thermodynamic consistency at DR as high as 750 by comparing with the coexisting values from Maxwell construction. The effects of Weber (We) number, Ohnesorge (Oh) number, density ratios (DR), viscosity ratios, off-center collision and droplets' initial position were discussed in details by showing the development of liquid fraction contours and the velocity vectors. The simulation results indicated: 1) by increasing of We number, the dynamic behaviors of droplets were changed from coalescence to flexible separation with the formation of satellite droplet; 2) with the increasing of Oh number, the degree of deformation of the droplet collisions became smaller; 3) the larger the gas viscosity was, the greater the resistance that the droplet movement would be; 4) the change of dynamic behaviors of droplet collisions when varying DR from 135 to 750 was negligible if other parameters and conditions were maintained the same; 5) for the off-center collisions with the same Oh number, increasing We number led to the formation of a long and thin "ligament" in between the droplets, which was finally separated into two satellite droplets. It is hoped that the SC pseudopotential MRT LBM model can advance the fundamental understanding of droplets collisions at large density ratios.