# On the effect of polydispersity and rotation on the Brinkman force induced by a cloud of particles on a viscous incompressible flow

## TL;DR

This paper extends the understanding of how a large cloud of particles, with varying shapes and rotations, collectively influences viscous flow by deriving a generalized Stokes-Brinkman limit incorporating particle shape and motion.

## Contribution

It generalizes previous results by including particles of arbitrary shapes and rotations, providing a more comprehensive model of particle-fluid interactions in the limit of many particles.

## Key findings

- Derived the limit Stokes-Brinkman system with shape and rotation effects.
- Extended previous models to include arbitrary particle shapes and rotations.
- Proved convergence of the fluid velocity to the new limit system.

## Abstract

In this paper, we are interested in the collective friction of a cloud of particles on the viscous incompressible fluid in which they are moving. The particles velocities are assumed to be given and the fluid is assumed to be driven by the stationary Stokes equations. We consider the limit where the number N of particles goes to infinity with their diameters of order 1/N and their mutual distances of order (1/N)^{1/3}. The rigorous convergence of the fluid velocity to a limit which is solution to a stationary Stokes equation set in the full space but with an extra term, referred to as the Brinkman force, was proven by Desvillettes, Golse and Ricci when the particles are identical spheres in prescribed translations. Our result here is an extension to particles of arbitrary shapes in prescribed translations and rotations. The limit Stokes-Brinkman system involves the particle distribution in position, velocity and shape, through the so-called Stokes' resistance matrices.