Three-component phase-field Lattice Boltzmann method with high density ratio and ability to simulate total spreading states

In this paper, a ternary phase-field based LBM, capable of handling high density ratios [O(1000)] and total spreading situations is presented. In order to improve the density ratio between three components, stable discretization incorporating mixed differentiating scheme (average of the biased and central schemes) is adopted, which instead of 8, involves 16 neighboring points to approximate the derivative terms. The multi-component Cahn-Hilliard equations are employed to track phasic evolution of the system. The bulk free energy in these equations is chosen in such a way that it enables the model to cope with total spreading problems, where one of the components is totally wetted by one, or both of the other fluids. Two LB equations are used to capture the interface between three incompressible-immiscible fluids, and another one for simulation of the hydrodynamic flow field. To demonstrate versatility and accuracy of the proposed model, a wide range of benchmark problems and numerical tests, including static and dynamic interaction of a bubble at liquid-liquid interface, ternary phase separation, binary and ternary Rayleigh-Taylor instability (RTI), and finally collision and coalescence between an oil droplet and a gas bubble that are rising in water due to the buoyancy force, are investigated. A good agreement is found between simulation results and available data/theoretical predictions. The simulation results of the bubble-droplet interaction reveals that the film drainage and coalescence times of the off-center collisions are higher compared to the head-on impacts, and these times increase with the horizontal distance separating the bubble and the droplet. (C) 2020 Elsevier Ltd. All rights reserved.