Patterns in Flowing Sand: Understanding the Physics of Granular Flow

TL;DR

This paper investigates the formation of longitudinal stripe patterns in dense granular flows on inclined planes, revealing how flow density influences instability and pattern formation through experimental and numerical methods.

Contribution

It introduces new experimental and numerical insights into the instability mechanisms causing stripe formation in granular flows, highlighting the role of flow density.

Findings

Stripe formation depends on flow density.

High-density flows form plug-like regions with boiling material.

Patterns resemble Leidenfrost effect phenomena.

Abstract

Dense granular flows are often unstable and form inhomogeneous structures. Although significant advances have been recently made in understanding simple flows, instabilities of such flows are often not understood. We present experimental and numerical results that show the formation of longitudinal stripes that arise from instability of the uniform flowing state of granular media on a rough inclined plane. The form of the stripes depends critically on the mean density of the flow with a robust form of stripes at high density that consists of fast sliding plug-like regions (stripes) on top of highly agitated boiling material - a configuration reminiscent of the Leidenfrost effect when a droplet of liquid lifted by its vapor is hovering above a hot surface.