Title: Modeling of granular flows in split-bottom Couette cells

Author (Talk): David Henann, MIT

Abstract:

For the past decade, split bottom Couette cells have been used to experimentally study shear bands in steady, slow, dense granular flows. Most notably, the widths of these shear bands are observed to depend upon the geometry of the Couette cell and the size of the grains. Local, rate independent continuum theories are incapable of describing shear bands with finite widths, and the challenge of modeling granular flows in split bottom geometries has remained open. Our work addresses this challenge. A recent nonlocal constitutive relation, based on extending nonlocal fluidity modeling of emulsions, has been shown to capture finite-size effects in simple, two-dimensional, steady granular flows. We assimilate this nonlocal rheology into a three-dimensional elastic-viscoplastic constitutive theory. The theory has been implemented in a finite element code, capable of addressing arbitrary three-dimensional boundary value problems. We present results from simulations of granular flows in split-bottom Couette cells using this modeling capability that quantitatively capture the experimentally-observed shear banding phenomena. Importantly, we are able to capture the error function nature of the surface angular velocity profiles as well as the cell height and grain diameter dependence of the shear band widths.