TY - JOUR

T1 - Shear-Rate-Independent Diffusion in Granular Flows

AU - Fan, Yi

AU - Umbanhowar, Paul B.

AU - Ottino, Julio M.

AU - Lueptow, Richard M.

N1 - Publisher Copyright:
© 2015 American Physical Society. © 2015 American Physical Society.

PY - 2015/8/18

Y1 - 2015/8/18

N2 - We computationally study the behavior of the diffusion coefficient D in granular flows of monodisperse and bidisperse particles spanning regions of relatively high and low shear rate in open and closed laterally confined heaps. Measurements of D at various flow rates, streamwise positions, and depths collapse onto a single curve when plotted as a function of γd¯2, where d¯ is the local mean particle diameter and γ is the local shear rate. When γ is large, D is proportional to γd¯2, as in previous studies. However, for γd¯2 below a critical value, D is independent of γd¯2. The acceleration due to gravity g and particle stiffness (or, equivalently, the binary collision time tc) together determine the transition in D between regimes. This suggests that while shear rate and particle size determine diffusion at relatively high shear rates in surface-driven flows, diffusion at low shear rates is an elastic phenomenon with time and length scales dependent on gravity (d¯/g) and particle stiffness (tcd¯g), respectively.

AB - We computationally study the behavior of the diffusion coefficient D in granular flows of monodisperse and bidisperse particles spanning regions of relatively high and low shear rate in open and closed laterally confined heaps. Measurements of D at various flow rates, streamwise positions, and depths collapse onto a single curve when plotted as a function of γd¯2, where d¯ is the local mean particle diameter and γ is the local shear rate. When γ is large, D is proportional to γd¯2, as in previous studies. However, for γd¯2 below a critical value, D is independent of γd¯2. The acceleration due to gravity g and particle stiffness (or, equivalently, the binary collision time tc) together determine the transition in D between regimes. This suggests that while shear rate and particle size determine diffusion at relatively high shear rates in surface-driven flows, diffusion at low shear rates is an elastic phenomenon with time and length scales dependent on gravity (d¯/g) and particle stiffness (tcd¯g), respectively.

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U2 - 10.1103/PhysRevLett.115.088001

DO - 10.1103/PhysRevLett.115.088001

M3 - Article

C2 - 26340210

AN - SCOPUS:84940704275

SN - 0031-9007

VL - 115

JO - Physical Review Letters

JF - Physical Review Letters

IS - 8

M1 - 088001

ER -