Response to perturbations for granular flow in a hopper

TL;DR

This study experimentally examines how dense granular flow in a conical hopper responds to symmetry-breaking perturbations, revealing secondary azimuthal circulation and velocity fluctuations, and tests the validity of continuum-based constitutive models.

Contribution

It provides experimental evidence for azimuthal circulation in perturbed granular hopper flow and evaluates constitutive relations against observed flow phenomena.

Findings

Secondary azimuthal circulation occurs with tilt perturbations.

Wall friction influences circulation suppression.

Velocity fluctuations increase with large tilt angles.

Abstract

We experimentally investigate the response to perturbations of circular symmetry for dense granular flow inside a three-dimensional right-conical hopper. These experiments consist of particle tracking velocimetry for the flow at the outer boundary of the hopper. We are able to test commonly used constitutive relations and observe granular flow phenomena that we can model numerically. Unperturbed conical hopper flow has been described as a radial velocity field with no azimuthal component. Guided by numerical models based upon continuum descriptions, we find experimental evidence for secondary, azimuthal circulation in response to perturbation of the symmetry with respect to gravity by tilting. For small perturbations we can discriminate between constitutive relations, based upon the agreement between the numerical predictions they produce and our experimental results. We find that the secondary circulation can be suppressed as wall friction is varied, also in agreement with numerical predictions. For large tilt angles we observe the abrupt onset of circulation for parameters where circulation was previously suppressed. Finally, we observe that for large tilt angles the fluctuations in velocity grow, independent of the onset of circulation.