2 Methods
2.1 Lattice Boltzmann Method
The LBM is a branch of computational fluid dynamics that has emerged as a popular technique to solve multiphase fluid flow systems in complex geometries because of its algorithmic simplicity (S. Chen & Doolen, 1998; Dou & Zhou, 2013; Jiang et al., 2014; Ramstad et al., 2010; Succi et al., 2010). LBM simulations treat fluids as a group consisting of fictive particles; the movement of these particles is simulated with a statistical approach. The movement of the bulk fluid is simulated from propagation and collision processes of the fictive particles (Huang et al., 2011). We chose the Rothman–Keller color gradient model (Tölke et al., 2006) to conduct the simulations because it can simulate a high fluid viscosity ratio with better accuracy than other LBM models (Ahrenholz et al., 2008; Yang & Boek, 2013). The color gradient model is so named because it graphically represents two-phase fluids as a mixture of a wetting and nonwetting fluid, assigned the colors blue and red, respectively (Huang et al., 2015). Our 3D simulations used the D3Q19 (3 dimensions, 19 velocity lattice) velocity model.