# A Hele-Shaw-Cahn-Hilliard model for incompressible two-phase flows with different densities

## TL;DR

This paper develops a diffuse interface model for incompressible two-phase flows with different densities in a Hele-Shaw cell, deriving it from existing models, proving solution existence, and demonstrating numerical simulations of complex flow phenomena.

## Contribution

It introduces a new diffuse interface model for two-phase flows with density differences in Hele-Shaw geometry, extending previous models and analyzing their solutions.

## Key findings

- Derived a simplified diffuse interface model for non-matched densities.
- Proved the existence of weak solutions for the model.
- Performed numerical simulations showing bubble rise and fingering instabilities.

## Abstract

Topology changes in multi-phase fluid flows are difficult to model within a traditional sharp interface theory. Diffuse interface models turn out to be an attractive alternative to model two-phase flows. Based on a Cahn-Hilliard-Navier-Stokes model introduced by Abels, Garcke and Gr\"{u}n (Math. Models Methods Appl. Sci. 2012), which uses a volume averaged velocity, we derive a diffuse interface model in a Hele-Shaw geometry, which in the case of non-matched densities, simplifies an earlier model of Lee, Lowengrub and Goodman (Phys. Fluids 2002). We recover the classical Hele-Shaw model as a sharp interface limit of the diffuse interface model. Furthermore, we show the existence of weak solutions and present several numerical computations including situations with rising bubbles and fingering instabilities.