# A comparative study of fluid-particle coupling methods for fully resolved lattice Boltzmann simulations

## TL;DR

This paper systematically compares two fluid-particle coupling methods in lattice Boltzmann simulations, highlighting their accuracy differences and emphasizing the importance of resolution choice for reliable fluid-solid suspension modeling.

## Contribution

It provides a detailed comparison of the momentum exchange and partially saturated cells methods, including their accuracy and resolution requirements for fully resolved particulate simulations.

## Key findings

- Momentum exchange method is more accurate for streamwise velocity.
- Partially saturated cells method better predicts spanwise velocity.
- Resolution of at least 24 cells per sphere diameter is needed for errors below 5%.

## Abstract

The direct numerical simulation of particulate systems offers a unique approach to study the dynamics of fluid-solid suspensions by fully resolving the submerged particles and without introducing empirical models. For the lattice Boltzmann method, different variants exist to incorporate the fluid-particle interaction into the simulation. This paper provides a detailed and systematic comparison of two different methods, namely the momentum exchange method and the partially saturated cells method by Noble and Torczynski. Three subvariants of each method are used in the benchmark scenario of a single heavy sphere settling in ambient fluid to study their characteristics and accuracy for particle Reynolds numbers from 185 up to 365. The sphere must be resolved with at least 24 computational cells per diameter to achieve velocity errors below 5%. The momentum exchange method is found to be more accurate in predicting the streamwise velocity component whereas the partially saturated cells method is more accurate in the spanwise components. The study reveals that the resolution should be chosen with respect to the coupling dynamics, and not only based on the flow properties, to avoid large errors in the fluid-particle interaction.