Multiple solutions for granular flow over a smooth two-dimensional bump
Journal: Journal of Fluid Mechanics
Publication Date: 25 March, 2017
Department of: Mathematics
How to control the flow of granular materials
Over forty percent of all materials used by industry are made of particles. Understanding how such granular materials flow is therefore of fundamental importance in a wide range of applications from the bulk chemical, mining and construction industries, to pharmaceuticals, food and agriculture. Now researchers at the University of Manchester have used a combination of small scale experiments, continuum theory and numerical simulations to investigate a granular chute flow – one in which a liquid-like avalanche of grains flows over a smooth bump. Intriguingly, for the same upstream conditions, there are two stable steady-state solutions, one in which the rapid avalanche flows over the bump and forms an airborne jet and another in which there is a shock wave upstream of the bump, where the thickness suddenly increases and the velocity is decreased. In the latter case, the flow stays attached to the chute base and air entrainment is minimized. This is important for controlling the speed of flows in industrial chute flows as well as reducing dust production when filling containers. For an empty chute the jet develops naturally, but the shock can be triggered by placing a small erodible deposit of grains upstream of the bump, or briefly blocking the flow. On the geophysical scale this work has important applications to the design of snow avalanche defences, since shock waves dissipate significant amounts of energy and slow the flow.