Abstract
This paper is concerned with the physical mechanisms controlling shear-induced diffusion in dense granular flows. The starting point is that of the granular random walk occurring in diluted granular flows, which underpins Bagnold’s scaling relating the coefficient of self-diffusion to the grain size and shear rate. By means of DEM simulations of plane shear flows, we measure some deviations from this scaling in dense granular flows with and without contact adhesion. We propose to relate these deviations to the development of correlated motion of grains in these flows, which impacts the magnitude of grain velocity fluctuations and their time persistence.
Highlights
This paper is concerned with the physical mechanisms controlling shear-induced diffusion in dense granular flows
This reflects the spontaneous development of transient clusters of grains, which move as a quasi-rigid body the case of a plane shear flow: when a packing is subjected to some shear deformation, grains diffuse in the direction transverse to shear
In shear flows the grain size d and the shear rate γare two elementary scales from which one can dimensionally build a macroscopic coefficient of diffusion D [1,2,3,4,5]: during a finite period of time These clusters introduce a meso-length scale that is larger than a grain and a characteristic time scale that is that of their lifetime T
Summary
The first observation is that cohesion enhances the diffusivity, regardless of the inertial number. Within the explored range of parameters, this enhancement is significant: it can reach an order of magnitude. I), both for cohesionless and cohesive grains. There is a deviation from that scaling at low inertial numbers: the diffusivity becomes dependent of. I and the ratio increases as the inertial number decreases
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