Abstract
Cylindrical containers with a rotating bottom disk (so-called split-bottom geometry) are well established devices to shear granular materials in a continuous way, and to generate well-defined localized shear bands in the granular bed. When material composed of shape-anisotropic grains is sheared in such a container, a secondary flow is generated that leads to the formation of a considerable heap of material near the rotation center. We demonstrate that this effect can be found not only with prolate grains, as shown in a previous study, but also for oblate particle shapes. In addition, the quantitative influence of geometric and dynamic parameters is studied systematically. It is shown that the fill height of the container has considerable influence on the time scale for heap formation, but much less effect on the heap height. Results of numerical simulations agree with the experimental findings and provide insight in the particle dynamics.
Highlights
Granular flows are present in countless processes encountered in geology, transport of materials like sand, coal or ores, and agricultural products
We discuss experiments in the geometry of Figure 1a: The formation of the heap extracted from the optical analysis of the surface profile is shown in Figure 3 for particles of different aspect ratios
Heaping is observed for all investigated anisometric grain types, there is no clear trend in the final heap height vs. particle aspect ratio
Summary
Granular flows are present in countless processes encountered in geology, transport of materials like sand, coal or ores, and agricultural products. It affects our everyday life in the kitchen or offices whenever we stir or shake grainy matter or pour it out of a container. While flow in Newtonian fluids has been well understood for centuries, and even many non-Newtonian flow phenomena are well characterized in liquids, granular flows have still preserved their mysteries to a great deal. Different aspects of granular dynamics were discussed in books and review articles Peculiarities of shape-anisotropic granular matter have been reviewed recently [6], with focus on specific packing problems, shear flow, alignment and orientational order
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