Complex Flow Dynamics in Dense Granular Flows: Part I — Experimentation; Part II — Simulations

PART I: By applying a methodology useful for analysis of complex fluids based on a synergistic combination of experiments, computer simulations and theoretical investigation, a model was built to investigate the fluid dynamics of granular flows in an intermediate regime where both collisional and frictional interactions may affect the flow behavior. In Part I, the viscoelastic behavior of nearly identical sized glass balls during a collision, have been studied experimentally using a modified Newton’s Cradle device. Analyzing the results of the measurements, by employing a numerical model based on finite element methods, the viscous damping coefficient was determined for the glass balls. Power law dependence was found for the restitution coefficient on the impact velocity. In order to obtain detailed information about the interparticle interactions in dense granular flows, a simplified model for collisions between particles of a granular material was proposed to be of use in molecular dynamic simulations, discussed in Part II. PART II: By applying a methodology useful for analysis of complex fluids based on a synergistic combination of experiments, computer simulations, and theoretical investigation, a model was built to investigate the fluid dynamics of granular flows in an intermediate regime, where both collisional and frictional interactions may affect the flow behavior. In Part I, experiments were described using a modified Newton’s Cradle device to obtain values for the viscous damping coefficient, which are scarce in the literature. In this paper, molecular dynamic simulations were performed using the simplified model for collisions between particles, developed in Part I, to obtain detailed information about the interparticle interactions. This information was used to develop a continuum model for granular flows, accounting for both collisional and frictional interactions between particles. To validate the continuum model, simulations were performed for the specific case of granular flow in a rapidly spinning bucket. The model was able to reproduce experimentally observed flow phenomena in buckets spinning at high frequencies (higher than 50 Hz), such as the transition from a cusp to a depression in the center of the bucket with increasing rotation rate. This agreement suggests that the model may be a useful tool for the prediction of dense granular flows in industrial applications, but highlights the need for further experimental investigation of granular flows in order to refine the model.