(320f) Continuum Simulations of Dense Granular Flow Near the Maximum Packing Limit

The rheology and hydrodynamics of powder flow are critical in many industrial processes such as agricultural and pharmaceutical production, and petrochemical refining. Continuum simulations solve the averaged equations for conservation of mass and momentum by treating the granular medium as a continuum and can predict granular hydrodynamics. A comparison of continuum simulations of silo discharge (Vidyapati et al. 2013) with experimental data and discrete element model simulations indicates that they are limited in their accuracy of predicted discharge rates by the constitutive model for granular stress. Specifically, accurate representation of the intermediate regime of granular flow, which lies between the rapid granular regime and the quasi-static regime, is needed for predictive accuracy. One of the challenges in incorporating newly proposed constitutive models for the granular stress in continuum simulations, which account for intermediate regime behavior (Chialvo et al. 2012, Sun et al. 2011, Vidyapati et al. 2016) is ensuring their realizable behavior near the maximum packing limit. Realizability in this context means guaranteeing that the solid volume fraction is always non-negative and does not exceed its theoretical maximum value without ad hoc modifications. The behavior of continuum solvers near the packing limit depends on the constitutive model for the granular pressure as a function of solid volume fraction. As the solid volume fraction approaches the maximum packing limit, there is a threshold above which the granular material behaves like an incompressible fluid. The equations also change type from variable density to incompressible at this incompressible threshold. We report solutions to a one-dimensional (1-D) granular flow illustrating this transition and develop a computational scheme to implement this in 3-D continuum simulations.