Comparison of Contact Angle Models in Two-Phase Flow Simulations Using a Conservative Phase Field Equation

Abstract

In phase field methods based on a second-order Allen-Cahn (AC) equation, contact angles are prescribed mostly via a geometric formulation. However, it is of great interest to utilize the surface-energy formulation, which is often employed in the Cahn-Hilliard (CH) phase field method, in the AC phase field method. This article thus put forward a surface-energy formulation of contact angles. The model was compared with the geometric one in a number of impact problems, including both normal and oblique impacts. The governing equations were discretized using a finite difference method on a half-staggered grid. The Navier–Stokes equation was tackled using an explicit projection method. The major findings are as follows. First, the geometric model can maintain a fixed contact angle throughout contact line motion, while the surface-energy one predicts a changeable contact angle, with a fluctuation of about 5°. In the oblique drop impact, contact angle hysteresis was captured even if a static contact angle was applied in the surface-energy formulation.