# Segregation of large particles in dense granular flows: A granular Saffman effect?

## TL;DR

This paper investigates the inertial lift forces acting on large particles in dense granular flows, revealing a similarity to the Saffman effect in fluids and suggesting new insights into particle segregation mechanisms.

## Contribution

It introduces a scaling law for lift forces in granular flows analogous to the Saffman effect, highlighting inertial origins and anisotropic stress fields affecting segregation.

## Key findings

- Lift force scales with velocity lag similar to Saffman effect
- Anisotropic stress field surrounds large particles
- Implications for modeling particle segregation in granular flows

## Abstract

We report on the scaling between the lift force and the velocity lag experienced by a single particle of different size in a monodisperse dense granular chute flow. The similarity of this scaling to the Saffman lift force in (micro) fluids, suggests an inertial origin for the lift force responsible for segregation of (isolated, large) intruders in dense granular flows. We also observe an anisotropic pressure/stress field surrounding the particle, which potentially lies at the origin of the velocity lag. These findings are relevant for modelling and theoretical predictions of particle-size segregation. At the same time, the suggested interplay between polydispersity and inertial effects in dense granular flows with stress- and strain-gradients, implies striking new parallels between fluids, suspensions and granular flows with wide application perspectives.