Collisional regime during the discharge of a 2D silo

TL;DR

This study uses molecular dynamics simulations to explore the collisional particle dynamics near the outlet of a 2D silo, revealing a smooth transition between clogging and flow regimes without a critical outlet size.

Contribution

It provides the first detailed analysis of collisional dynamics near the outlet, challenging the idea of a critical outlet size for clogging.

Findings

Transition from clogging to flow is smooth in collisional variables

No critical outlet size separates clogging and flow regimes

Clogging can occur at any outlet size

Abstract

The present work reports a novel investigation into the collisional dynamics of particles in the vicinity of the outlet of a 2D silo using molecular dynamics simulations. Most studies on this granular system focus in the bulk of the medium. In this region contacts are permanent or long-lived, so continuous approximations are able to yield results for velocity distributions or mass flow. Close to the exit, however, the density of the medium decreases and contacts are instantaneous. Thus, the collisional nature of the dynamics becomes significant, warranting a dedicated investigation as carried out in this work. More interesting, the vicinity of the outlet is the region where the arches that block the flow for small apertures are formed. It is found that the transition from the clogging regime (at small apertures) to the continuous flow regime is smooth in collisional variables. Furthermore, the dynamics of particles as reflected by the distributions of the velocities is as well unaffected. This result implies that there is no critical outlet size that separates both regimes, as had been proposed in the literature. Instead, the results achieved support the alternative picture in which a clog is possible for any outlet size.