Influence of grain bidispersity on dense granular flow in a two dimensional hopper

TL;DR

This study uses discrete element simulations to explore how bidispersity affects dense granular flow in a 2D hopper, revealing optimal flow conditions and structural influences on flow patterns.

Contribution

It demonstrates how adding a small fraction of large grains enhances flow rate and links flow properties to local structural arrangements and force arch formation.

Findings

Maximum flow rate occurs with a small fraction of large grains added.

Flow properties are closely related to local force arch and packing structure.

Transition from mass flow to funnel flow is influenced by packing order and occurs earlier with structural changes.

Abstract

Discrete element method is conducted to investigate the bidisperse dense granular flow having big and small grains in a two dimensional hopper. A half-circular dynamical force arch is observed above the outlet and Beverloo's law is verified to describe the relationship between flow rate and outlet size. The bidisperse flow can reach the maximum flow rate when a small fraction of big grains is added into the monodisperse flow with only small grains. The distributions of contact force, packing fraction and grain velocity indicate that the flow properties in the hopper are closely related to the local flow characteristics of the key area which almost overlaps with the force arch. The interior packing structures, i.e., ordered arrangement for monodisperse flow and disordered arrangement for bidisperse flow, play a dominant role in the flow pattern transition from mass flow to funnel flow. The earlier occurrence of the transition can effectively increase the grain velocity and therefore improve the flow rate.