Growing length scale in gravity-driven dense granular flow

TL;DR

This study uses simulations to analyze how velocity and stress fluctuations in dense granular flow become increasingly correlated as the system approaches jamming, revealing a growing length scale and time scale.

Contribution

It introduces a detailed simulation approach to quantify the growth of correlation length and time scales near jamming in gravity-driven granular flow.

Findings

Correlation length and time scale increase as jamming approaches

Velocity and stress fluctuations become more correlated

A growing length scale is observed near the jamming transition

Abstract

We report simulations of a two-dimensional, dense, bidisperse system of inelastic hard disks falling down a vertical tube under the influence of gravity. We examine the approach to jamming as the average flow of particles down the tube is slowed by making the outlet narrower. Defining coarse-grained velocity and stress fields, we study two-point temporal and spatial correlation functions of these fields in a region of the tube where the time-averaged velocity is spatially uniform. We find that fluctuations in both velocity and stress become increasingly correlated as the system approaches jamming. We extract a growing length scale and time scale from these correlations.