Interfaces determined by capillarity and gravity in a two-dimensional porous medium

TL;DR

This paper models the interface between water and air in a two-dimensional porous medium, analyzing how capillarity and gravity influence the shape and probability of different interface configurations across various regimes.

Contribution

It identifies four asymptotic regimes based on the Bond number and container size, providing probabilistic descriptions of interface configurations in each regime.

Findings

Gravity-dominated regimes favor near-horizontal interfaces with high probability.

Capillarity-dominated regimes favor interfaces close to smooth curves with high probability.

Large container size allows probabilistic description of deviations from ideal interface shapes.

Abstract

We consider a two-dimensional model of a porous medium where circular grains are uniformly distributed in a squared container. We assume that such medium is partially filled with water and that the stationary interface separating the water phase from the air phase is described by the balance of capillarity and gravity. Taking the unity as the average distance between grains, we identify four asymptotic regimes that depend on the Bond number and the size of the container. We analyse, in probabilistic terms, the possible global interfaces that can form in each of these regimes. In summary, we show that in the regimes where gravity dominates the probability of configurations of grains allowing solutions close to the horizontal solution is close to one. Moreover, in such regimes where the size of the container is sufficiently large we can describe deviations from the horizontal in probabilistic terms. On the other hand, when capillarity dominates while the size of the container is sufficiently large, we find that the probability of finding interfaces close to the graph of a given smooth curve without self-intersections is close to one.