Lattice Boltzmann simulation of droplet collisions at various angles in the presence of a non-condensable gas

Due to its simple concept and high computational efficiency, the pseudo-potential multiphase lattice Boltzmann (LB) model applied to high-density two- component flow has attracted great attention in recent years. In this work, a multi-component/multi-phase (MCMP) LB method with gas/liquid coexistence is proposed. Two state equations are incorporated in the pseudo-potential function, namely the Peng-Robinson (PR) state equation for water and the ideal gas state equation for non-condensable gas (NCG). Based on this newly developed MCMP LB model, the collision of two equal-sized liquid droplets in the presence of NCG is simulated. By simulating the state of stationary liquid droplets and the collision characteristics of the water droplets collision in air, the density distribution of gas/liquid, droplet sizes, ambient temperature, pressure difference inside and outside the droplets, and the regimes of collision outcomes exhibited by two water droplets colliding in air are numerically obtained. The relationships between various parameters and the collision outcomes are in good agreement with an existing analytical model, validating the correctness and accuracy of this newly developed MCMP LB model. Since this novel model does not involve any approximation/assumption or use empirical correlations for interface mass transfer, the results can be considered as the first attempt at direct numerical simulation of droplet collisions in the presence of NCG.