# Modelling ternary fluids in contact with elastic membranes

## TL;DR

This paper introduces a thermodynamically consistent model for simulating ternary fluid interactions with elastic membranes, combining lattice Boltzmann and immersed boundary methods for versatile fluid-structure interaction analysis.

## Contribution

A novel integrated modeling framework for ternary fluids and elastic membranes using lattice Boltzmann and immersed boundary methods.

## Key findings

- Validated model with elastic capsule at fluid interface
- Achieved Galilean invariance in simulations
- Demonstrated versatility with deformable capsule capillary bridge

## Abstract

We present a thermodynamically consistent model of a ternary fluid interacting with elastic membranes. Following a free-energy modelling approach and taking into account the thermodynamics laws, we derive the equations governing the ternary fluid flow and dynamics of the membranes. We also provide the numerical framework for simulating such fluid-structure interaction problems. It is based on the lattice Boltzmann method, employed for resolving the evolution equations of the ternary fluid in an Eulerian description, coupled to the immersed boundary method, allowing for the membrane equations of motion to be solved in a Lagrangian system. The configuration of an elastic capsule placed at a fluid-fluid interface is considered for validation purposes. Systematic simulations are performed for a detailed comparison with reference numerical results obtained by Surface Evolver, and the Galilean invariance of the proposed model is also proven. The proposed approach is versatile, and a wide range of geometries can be simulated. To demonstrate this, the problem of a capillary bridge formed between two deformable capsules is investigated here.