CFD SIMULATION OF MICROSCOPIC TWO-PHASE FLUID MOTION ON SOLID BODY WITH EDGES AND HETEROGENEOUSLY-WETTED SURFACE USING PHASE-FIELD MODEL

Our objective in this study is to examine the applicability of a computational fluid dynamics (CFD) method to simulation of motions of microscopic two-phase fluid on solid surfaces with edges for evaluating fluidic devices and for predicting underground fluid flows through porous media. The method adopts the phase-field model (PFM) for fluid-fluid interfacial dynamics and the lattice-Boltzmann method (LBM) as numerical scheme for solving a set of two-phase fluid-dynamics equations. Based on the free-energy theory, the PFM reproduces an interface as a finite volumetric zone between phases without imposing topological constraints on interface as phase boundary. Wettability of solid surface to fluid is taken into account through minimizing the free energy of the fluid plus the surface energy per unit area. The LBM assumes that a macroscopic fluid consists of fictitious mesoscopic particles repeating collisions with each other and rectilinear translations with an isotropic discrete velocity set. The simply-iterative particle-kinematic operation in a semi-Lagrange form is useful for high-performance computing of complex fluid flow systems. The CFD method therefore has an attractive advantage over the others, efficient simulation of motions of multiple fluid particles on partially-wetted and textured solid surfaces. The major findings in preliminary immiscible liquid-liquid simulations are as follows: (1) the method simulated well departure of single droplet from flat surface due to buoyancy in agreement with the semi-empirical prediction; (2) the droplet had larger static contact angle on hydrophobic grooved surface than that on flat surface in a similar way with available data; (3) the droplet moved more easily under external forcing in the tangential direction to the grooves than that under forcing in the normal direction in qualitative agreement with experimental observations.