On an averaged model for immiscible two‐phase flow with surface tension and dynamic contact angle in a thin strip

We consider a model for the flow of two immiscible fluids in a two‐dimensional thin strip of varying width. This represents an idealization of a pore in a porous medium. The interface separating the fluids forms a freely moving interface in contact with the wall and is driven by the fluid flow and surface tension. The contact‐line model incorporates Navier‐slip boundary conditions and a dynamic and possibly hysteretic contact angle law. We assume a scale separation between the typical width and the length of the thin strip. Based on asymptotic expansions, we derive effective models for the two‐phase flow. These models form a system of differential algebraic equations for the interface position and the total flux. The result is Darcy‐type equations for the flow, combined with a capillary pressure–saturation relationship involving dynamic effects. Finally, we provide some numerical examples to show the effect of a varying wall width, of the viscosity ratio, of the slip boundary condition as well as of having a dynamic contact angle law.