Discretization and Kinematic Effects of Meniscus Motion on Apparent Contact Angle During Rise in a Wide Capillary

Abstract

Capillary effects govern fluid distribution in reservoir rocks and fluid transport in various porous systems. Capillarity and wettability are linked through the intricate interplay of interfacial tension, surface wettability, and gravity. Quantitative evaluation of wettability conditions, using high-resolution experimental techniques especially in dynamically changing systems, often relies on determination of contact angle through the measurement of interfacial curvature. Here, we use OpenFOAM simulations of capillary rise in a straight vertical channel (two parallel plates) to investigate the effects of inertia, surface tension and gravity on the spatially and temporally resolved meniscus curvature and apparent contact angle. The variations of the apparent contact angle, inferred from the local curvature, are related to kinematic elements—velocity, acceleration, and acceleration rate—through the simulated capillary rise. Simulations are verified against analytical solutions for both equilibrium height and contact angle and compared to theoretically predicted oscillation dynamics for the 1D case. Results demonstrate hysteresis-like behaviour of the apparent contact angle, albeit to a smaller degree than the typical difference between advancing and receding contact angles and reveal that the apparent contact angle evolves systematically with interface velocity and acceleration. Two further sources of deviation are also identified—non-circular meniscus geometry and transient capillary-wave modulation—each an order of magnitude smaller than the kinematic deviation but representing systematic, geometry-induced contributions to image-based contact angle measurements. These findings underscore the importance of resolving transient interface geometry and kinematic effects when interpreting pore-scale wettability from curvature-based measurements.