Self-diffusion in inhomogeneous granular shearing flows

In this Letter, we discuss how flow inhomogeneity affects the self-diffusion behavior in granular flows. Whereas self-diffusion scalings have been well characterized in the past for homogeneous shearing, the effect of shear localization and nonlocality of the flow has not been studied. We, therefore, present measurements of selfdiffusion coefficients in discrete numerical simulations of steady, inhomogeneous, and collisional shearing flows of nearly identical, frictional, and inelastic spheres. We focus on a wide range of dense solid volume fractions, that correspond to geophysical and industrial shearing flows that are dominated by collisional interactions. We compare the measured values first with a scaling based on shear rate and, then, on a scaling based on the granular temperature. We find that the latter does much better than the former in collapsing the data. The results lay the foundations of diffusion models for inhomogeneous shearing flows, which should be useful in treating problems of mixing and segregation.

Automated summary

In this letter, the effects of flow inhomogeneity on self-diffusion behavior in granular flows are discussed. Measurements of self-diffusion coefficients in steady, inhomogeneous, and collisional shearing flows are presented. The results show that a scaling based on the granular temperature is more effective in describing the self-diffusion behavior. These findings lay the groundwork for diffusion models in inhomogeneous shearing flows, which are important for understanding mixing and segregation.