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Unsteady granular flows in a rotating tumbler
Nicholas A Pohlman1, Julio M Ottino, Richard M Lueptow
1Department of Mechanical Engineering, Northern Illinois University, DeKalb, Illinois 60015, USA. npohlman@niu.edu
Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|November 13, 2009
Summary
Unsteady granular flow in rotating tumblers exhibits dynamic properties like phase lag and resonance. This analysis can help characterize the flowability and rheology of granular materials.
Area of Science:
- Physics
- Engineering
- Materials Science
Background:
- Steady granular flow in rotating tumblers is well-understood.
- Unsteady, time-varying granular flow dynamics remain less explored.
Purpose of the Study:
- Investigate the linear response of granular flow under unsteady conditions.
- Analyze periodic and step changes in tumbler rotational speed.
- Explore the impact of tumbler radius, particle size, and forcing frequency.
Main Methods:
- Utilized quasi-two-dimensional rotating tumblers.
- Applied sinusoidal variations and step changes to rotational speed.
- Examined variations in tumbler radius, particle size, and forcing frequency.
Main Results:
- Flow fastest at the free surface with linear velocity profiles.
- Flowing layer depth varied by 2-5 particle diameters.
- Phase lag increased with forcing frequency; resonance behavior observed in amplitude responses.
- Overshoot (up to 35%) and rapid rise times (0.2-0.7 s) noted for step changes.
Conclusions:
- Unsteady forcing introduces dynamic properties to granular flow.
- Phase lag correlates with particle contact numbers.
- Analysis of unsteady granular flow can characterize material flowability and rheology.
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