Particle dynamics modeling of boundary effects in granular couette flow
Department of Mechanical and Industrial Engineering
Doctor of Philosophy
Rosato, Anthony D.
Dave, Rajesh N.
Fischer, Ian Sanford
Dynamics of a Particle
Bulk Solid Flow
Bulk Solid Handling
Boundary Value Problem
This study provides insights in understanding boundary effects on the flow of dry granular materials composed of identical, smooth, inelastic spheres between parallel, bumpy walls in the absence of gravity. The results of this study are useful in providing a basis upon which developing theories can be modified as well as substantiating previous and current experiments. This in turn has a major importance in many industries which are concerned with handling of particulates, such as coal, mineral processing, powder metallurgy, and agriculture.
The particle dynamics or discrete element method is used to model this flow, thereby providing a means of obtaining macroscopic information from the detailed particle-level multi-body dynamics. A shearing flow is induced by allowing the upper and lower walls to move with the same constant velocity in opposite directions. The wall geometry is characterized by several parameters - the spacing between the wall half-spheres and their geometric arrangement, diameter ratio of the wall to flow spheres, shear gap height and particle inelasticity measured by a constant normal restitution coefficient. Boundary roughness is either increased or decreased by appropriately adjusting the spacing between wall half-spheres or by changing the diameter ratio.
For "small" systems, a large stress drop occurs for dence [sic] flows when the wall particles are tightly packed. In this case, a layered shearing flow is present. However, as the shear gap height is increased while maintaining the same wall conditions, the stress drop does not occur.
Computed wall stress components and slip velocities are very sensitive to boundary parameters. The ratio of shear to normal wall stresses is found to be independent of shear gap heights for fixed wall conditions. As wall roughness increases or flow particles become more elastic, slip velocity decreases thereby reducing the effectiveness of the walls in supplying momentum to the flow. A pronounced reduction in slip velocity is observed with increasing wall roughness for relatively elastic particles.
njit-etd1992-011 (301 pages ~ 9,769 KB pdf)
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Created August 22, 2001