Internal Waves Control Bulk Flow in Silos

TL;DR

This study experimentally investigates internal wave phenomena in granular silo discharges, revealing a deceleration wave whose frequency decreases with cohesion and is unaffected by outlet size.

Contribution

It introduces the observation of a deceleration wave in granular silos and characterizes its frequency dependence on cohesion and outlet size.

Findings

Deceleration wave propagates from outlet to top during discharge.

Wave emission frequency decreases with medium cohesion.

Frequency is independent of outlet size.

Abstract

We experimentally measure paticle acceleration within the bulk during the discharge of a granular silo. We highlight the existence of a deceleration wave emerging at the outlet level near the dead zone and propagates toward the top of the medium. The wave emission frequency is extracted from spatiotemporal diagrams of the Eulerian instantaneous acceleration profiles. Surprisingly, we find that this frequency decreases with the cohesion of the medium and is independent of the outlet size.