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Flow-induced agitations create a granular fluid: effective viscosity and fluctuations.
Kiri Nichol1, Martin van Hecke
1Kamerlingh Onnes Lab, Universiteit Leiden, Postbus 9504, 2300 RA Leiden, The Netherlands.
Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|September 26, 2012
Summary
Granular materials exhibit liquid-like behavior, with viscosity dependent on stirring and probe properties. Nonlocal effects link fluid-like behavior to agitation, mediated by Gaussian fluctuations.
Area of Science:
- Physics
- Materials Science
- Rheology
Background:
- Understanding granular material flow is crucial for various industrial processes.
- Characterizing the rheology of granular media under dynamic conditions remains a challenge.
Purpose of the Study:
- To investigate the mechanical response of quiescent granular regions subjected to localized stirring.
- To determine the effective viscosity and rheological properties of the fluidizing granular medium.
- To explore the nature of granular fluctuations and their role in nonlocal interactions.
Main Methods:
- Utilizing a split-bottom shear cell to fluidize granular media via localized stirring.
- Employing cylindrical probes to measure vertical motion (rising, sinking, floating) in quiescent regions.
- Analyzing drag forces on probes to define effective viscosity and probe rheological behavior.
Main Results:
- Granular material exhibits liquid-like behavior, with probe buoyancy following Archimedes' law.
- Effective viscosity is inversely proportional to stirring rate and depends on probe size and mass, indicating complex rheology.
- Granular fluctuations display diffusive and subdiffusive behavior, saturating at longer times, and are directly linked to viscosity.
Conclusions:
- Localized stirring induces nonlocal fluid-like behavior in granular media.
- The system's rheology is complex, deviating from simple Newtonian fluid behavior.
- Granular fluctuations play a key role in mediating nonlocal interactions and influencing effective viscosity.
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