Investigation of stresses in a Couette shear cell using Discrete Element Modeling

Abstract

Granular flows are frequently seen in industry today but their complex nature makes it difficult to formulate general macroscopic governing relations. Effort has therefore been given to investigate these flows on detailed microscopic level and from that draw conclusions of the corresponding macroscopic behavior. In this project, a Discrete Element Modeling (DEM) method is used to simulate dry granular flow in a Couette geometry. The system is dense with particle volume fractions of up to α = 0:81. To accurately describe contact forces on the particles a soft-sphere model is used. Macroscopical system stresses are formulated based on the forces on each particle. Shear stresses are evaluated as a function of characteristic properties of the system, including volume fraction, the shear rate and particle friction. Clear trends on magnitude of the stresses are found for all considered properties. A higher volume fraction, shear rate or friction are shown to result in higher stress levels in the system. Further, tendencies on shear stress related to average normal stress are shown for volume fraction. Where a higher volume fraction results in a relatively lower shear stress. To investigate the presence of mono sized or of particles of different size in the system, a bimodal distribution of particle sizes is compared to a single size setup. For the distributed particle size calculations the stress magnitude coincide with the single size simulation, whereas the shear to normal stress ratios decrease faster in radial direction from the inner ring.