Transient Rheology of Immersed Granular Materials

TL;DR

This paper develops a unified rheological framework for immersed granular flows, combining experiments and simulations to introduce a new dimensionless number that captures transient behavior across different regimes.

Contribution

It introduces a novel dimensionless number $\\mathcal{G}$ that unifies inertial and viscous rheology in transient immersed granular flows, supported by experimental and simulation data.

Findings

The dimensionless number $\mathcal{G}$ smoothly transitions between inertial and viscous regimes.

Kinetic stresses are essential for a universal rheological relation.

The framework improves understanding of granular-fluid mixtures in natural and engineering contexts.

Abstract

In this letter, we investigate the transient rheological behavior of immersed granular flows using both experiments of submerged granular column collapses and corresponding numerical simulations. The simulations are performed with the lattice-Boltzmann method (LBM) coupled with the discrete element method (DEM) and provide a significant amount of data of the stress and deformation conditions at different positions and times during the granular collapse. We derive a new dimensionless number $\mathcal{G}$ that can unify the rheology of transient granular flows in different regimes for all the simulation data points. $\mathcal{G}$ smoothly transforms from an inertial number into a viscous number, unifying both extremes of the rheology law. We also show the need to introduce the kinetic stresses to achieve a universal relation. The findings establish a transient constitutive framework for visco-inertial granular flows and are important for a better understanding of granular-fluid mixtures in both natural and engineering situations.