We investigate the effect of intergranular cohesive forces on the properties of self-diffusion in dense granular flows. The study is based on a series of simulated plane shear flows at different inertial and cohesion numbers, in which transverse diffusivities are measured. Results evidence an increase in diffusivity by up to two orders of magnitude when introducing cohesion. This strong effect is analysed using the Green–Kubo framework, expressing the diffusivity in terms of instantaneous grain velocity fluctuations and their time correlation. This analysis shows that cohesion, by forming enduring clusters in the flow, enhances the velocity fluctuations and their time persistence, which both contribute to enhancing grain mixing and self-diffusion.

Cohesive granular materials such as wet sand, snow, and powders can flow like a viscous liquid. However, the elementary mechanisms of momentum transport in such athermal particulate fluids are elusive....

PACS 47.56.+r -Flows through porous media PACS 47.60.Dx -Flows in ducts and channels PACS 89.75.Hc -Networks and genealogical trees Abstract -We investigate the hydraulic permeability of complex channel networks by expressing analytically the system tortuosity in terms of topology. The tortuosity is shown to be strongly dependent on the covariance between the flow velocity in the channels and their length, and we demonstrate that in isotropic networks no covariance means impermeability. The derived analytical expression for the tortuosity is assessed against numerical simulations of various proximity-based and topology-based isotropic complex networks, and is then used to explain why the permeability of the latter networks is typically lower than the former. The new formula and findings have vast applications in biology, geology, hydrology and in engineering transport systems.

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Granular materials are comprised of solid, athermal grains. Whilst immune to thermal motion, these grains move and diffuse when they undergo shear deformation. Here we introduce this process of shear-induced...