A study of the rheology and micro-structure of dumbbells in shear geometries

We study the flow of frictional, inelastic dumbbells made of two fused spheres of different aspect ratios down a rough inclined plane and in a simple shear cell, using discrete element simulations. At a fixed inclination angle, the mean velocity decreases, and the volume fraction increases significantly with increasing aspect ratio in the chute flow. At a fixed solid fraction, the shear stress and pressure decrease significantly with increasing aspect ratio in the shear cell flow. The micro-structure of the flowis characterized. The translational diffusion coefficient in the normal direction to the flowis found to scale as D-yy = b(gamma)over dotd(2), independent of aspect ratio, where b is a constant, (gamma)over dot is the shear rate, and d is the diameter of the constituent spheres of the dumbbells. The effective friction coefficient (mu, the ratio of shear stress to pressure) increases by 30%-35% on increasing the aspect ratio lambda, from 1.0 to 1.7, for a fixed inertial number I. The volume fraction (phi) also increases significantly with increasing aspect ratio, especially at high inertial numbers. The effective friction coefficient and volume fraction are found to follow simple scalings of the form mu = mu(I, lambda) and phi = phi (I, lambda) for all the data from both systems, and the results are in reasonable agreement with kinetic theory predictions at low I. The computational results are in reasonable agreement with the experimental data for flow in a rotating cylinder. Published by AIP Publishing.