Bottlenecks in granular flow: When does an obstacle increase the flowrate in an hourglass?

TL;DR

This study uses particle-based simulations to show that placing an optimized obstacle before a bottleneck can increase granular flowrate, revealing complex velocity-density interactions unlike traditional traffic models.

Contribution

It introduces a phenomenological velocity-density model for granular flow with obstacles, demonstrating flowrate enhancement through obstacle optimization.

Findings

Flowrate increases with obstacle placement and size.

Velocity-density relationship peaks at a critical density.

Hysteresis effects are observed due to particle-obstacle interactions.

Abstract

Bottlenecks occur in a wide range of applications from pedestrian and traffic flow to mineral and food processing. We examine granular flow across a bottleneck using particle-based simulations. Contrary to expectations we find that the flowrate across a bottleneck actually increases if an opti- mized obstacle is placed before it. The dependency of flowrate on obstacle diameter is derived using a phenomenological velocity-density relationship that peaks at a critical density. This relationship is in stark contrast to models of traffic flow, as the mean velocity does not depend only on density but attains hysteresis due to interaction of particles with the obstacle.