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

Abstract

This study aims to investigate binary droplet collision with large density ratios (DRs) via an improved pseudopotential multiple-relaxation-time (MRT) lattice Boltzmann method (LBM). This method can satisfy the thermodynamic consistency at a DR of 750 compared with the coexisting values from Maxwell construction. The effects of the Weber (We) number, Ohnesorge (Oh) number, DR, viscosity ratio, off-center collision, and the initial droplet position are discussed in detail by showing the development of liquid fraction contours and the velocity vectors. The simulation results indicate that (1) with an increase in the We number, the dynamic behavior of the droplets changed from coalescence to flexible separation with the formation of satellite droplets; (2) with an increase in the Oh number, the degree of deformation of the droplet collisions became smaller would become; (3) the larger the gas viscosity was, the greater the resistance of the droplet movement; (4) the change in the dynamic behavior of the droplet collisions were negligible when varying the DR from 135–750 if other parameters and conditions were maintained; and (5) for the off-center collisions with the same Oh number, an increasing We number led to the formation of a long and thin ‘ligament’ in between the droplets, which finally separated into two satellite droplets. It is hoped that this improved single-component pseudopotential MRT-LBM model can advance the fundamental understanding of droplet collisions with large DRs and low viscosities.