Shear Flows of Granular Materials

Citation

Campbell, Charles Soutter (1982) Shear Flows of Granular Materials. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/QZSF-E358. https://resolver.caltech.edu/CaltechETD:etd-11242003-104837

Abstract

Many of the macroscopic and microscopic features of shearing granular materials were observed during the course of this investigation.

The principal results were obtained from a computer simulation of the flows in an inclined chute, and in a Couette shear cell. The simulation followed the exact trajectories of two-dimensional discs through a control volume. Properties of the flow were obtained from temporal averages of the instantaneous particle properties. Macroscopic flow characteristics such as velocity and density profiles are presented. Because the simulation follows the exact mechanics of the particles it was also possible to investigate the statistical nature of granular flows. Towards this purpose velocity distributions, collision angle distributions and pair correlation functions were measured.

The results of the simulation draw a picture of a flowing granular material as a self-excited gas. There appears to be a "temperature" associated with the random motions of the particles, that is a product of gradients in the mean velocity field. An equation of state is proposed, involving this temperature, to describe the behavior of the density within the flow. A phenomenon reminscent of conduction is observed. The particle velocities appear to obey a Maxwellian distribution based on this temperature.

Preliminary experiments were also performed to investigate the flow of glass beads down inclined chutes. It is shown that the flows may be classified as either supercritical or subcritical depending on the local value of the Froude number, and that the classification had a strong influence on the flow properties. In addition, wall friction coefficients were determined.

Thesis Files