(448ae) Multi-Scale Approach to Developing Non-Spherical Particle Models for Realistic Granular Flow Simulations

Buettner, K. E., University of Florida
Guo, Y., Zhejiang University
Curtis, J. S., UC Davis
The simulation of granular flows can be performed with either a Lagrangian or Eulerian approach. The Lagrangian approach, i.e. discrete element method (DEM) simulations, has the ability to simulate realistic particle shapes, but only a limited number of particles can be simulated due to the high computational cost. The Eulerian approach, i.e. two-fluid simulations, can simulate large-scale granular flows, but the models in this approach typically assume that the particles are spherical. The spherical-particle assumption hampers the accuracy of two-fluid simulations, due to the fact that particle shape has a significant impact on flow behavior. As a result, better Eulerian models should be developed to account for the shape effect. This work focuses on the development of a workflow for the numerical modeling of non-spherical particle flow at a large scale. In this workflow, the DEM simulations are used to determine the terms in the granular kinetic theory for the description of non-spherical particle flow. The developed non-spherical particle models are then plugged into the two-fluid model for the large-scale simulations.  

Granular kinetic theory terms that are important for two-fluid simulations include: solid stress, collisional dissipation rate, and granular conductivity. The former two terms are dominant for dense granular flows. DEM simulations with the glued-sphere particle model and true cylinder model have been utilized to develop the solid stress and collisional dissipation rate models for elongated, rod-like particles. The developed models are implemented into a two-fluid model code for the simulations of rod-like particle flows. A validation study is presented that utilizes an experiment with monodisperse beds of cylindrical particles. The experiment involves the impingement of an air jet onto a particle bed, which produces a crater.  Varying flow rates and particle sizes with aspect ratios from 2 to 8 have been used. The depth of the crater over time is measured for each case. The air jet-induced particle bed cratering is simulated using the two-fluid code and the comparison of the experimental and simulated data is presented.