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Published on: February 6, 2014
Shear-driven segregation of dense granular mixtures in a split-bottom cell
1St. Anthony Falls Laboratory, Department of Civil Engineering, University of Minnesota, Minneapolis, Minnesota 55414, USA.
Summary
Shear-driven segregation in granular materials is less dramatic than previously thought. Gravity and convection rolls, not shear gradients alone, primarily cause observed segregation patterns.
Area of Science:
- Granular physics
- Complex systems
- Pattern formation
Background:
- Shear-driven segregation in dense granular mixtures is a key phenomenon in pattern formation.
- Previous studies suggested significant segregation effects solely due to shear gradients.
Purpose of the Study:
- To experimentally and computationally isolate segregation effects from shear gradients versus gravity.
- To investigate the mechanisms driving segregation in granular flows.
Main Methods:
- Utilized experimental and computational split-bottom cells to analyze segregation.
- Measured convection rolls and segregation flux in circular and parallel cell geometries.
Main Results:
- Shear gradient effects were less dramatic than anticipated.
- Observed segregation patterns were often orthogonal to the shear gradient's active flux.
- A toroidal convection roll, combined with gravity, explained horizontal segregation patterns in circular cells.
- Computational models showed subtle segregation flux from shear gradients in parallel cells.
Conclusions:
- Gravity and flow-induced convection rolls play a more significant role in segregation than shear gradients alone.
- Current kinetic theory predicting segregation direction based on binary collisions is insufficient.
- The direction of shear-driven segregation is dependent on flow characteristics, such as collisional or frictional dominance.
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