Two-phase flows through porous media described by a Cahn--Hilliard--Brinkman model with dynamic boundary conditions

TL;DR

This paper introduces a new diffuse-interface model for creeping two-phase flows in porous media, incorporating dynamic boundary conditions to better capture fluid-wall interactions and contact line dynamics.

Contribution

It develops a novel Cahn--Hilliard--Brinkman model with dynamic boundary conditions and proves existence and uniqueness of weak solutions for regular potentials.

Findings

Proved existence of global-in-time weak solutions.

Established uniqueness under additional assumptions.

Extended results to singular potentials via approximation.

Abstract

We investigate a new diffuse-interface model that describes creeping two-phase flows (i.e., flows exhibiting a low Reynolds number), especially flows that permeate a porous medium. The system of equations consists of a Brinkman equation for the volume averaged velocity field as well as a convective Cahn--Hilliard equation with dynamic boundary conditions for the phase-field, which describes the location of the two fluids within the domain. The dynamic boundary conditions are incorporated to model the interaction of the fluids with the wall of the container more precisely. In particular, they allow for a dynamic evolution of the contact angle between the interface separating the fluids and the boundary, and also for a convection-induced motion of the corresponding contact line. For our model, we first prove the existence of global-in-time weak solutions in the case where regular potentials are used in the Cahn--Hilliard subsystem. In this case, we can further show the uniqueness of the weak solution under suitable additional assumptions. Moreover, we further prove the existence of weak solutions in the case of singular potentials. Therefore, we regularize such singular potentials by a Yosida approximation, such that the results for regular potentials can be applied, and eventually pass to the limit in this approximation scheme.