One way that a granular flow differs from ordinary fluids is that its dynamics depends largely on the conditions at solid boundaries. For instance, the minimum thickness necessary to sustain a steady flow is a function of base roughness; the slip occurring at the base can modify the bulk rheological behavior, which changes the disorder flow state to a crystallized structure. Such a complicated dependency on solid boundaries in granular flows contrasts with the simple non-slip boundary condition in ordinary fluids.

Common boundary conditions at the base include flat, bumpy, and erodible bases, among wihch the bumpy base attracts most attentions in both experimental and numerical studies of granular flows.

The bumpiness of a boundary made of glued/fix particles depends not only on the size ratio between base and flow particles, but also the packing and layering of the base particles. The situation becomes more complicated if bi-dispersity exists in the bulk flows, which changes the relative roughness as segregation takes place.

In the continuum modeling of granular flows, the boundary condition is an important closure to the governing equations, which requirs the knowledge of slip/non-slip condition.

This project aims to understand the effect of base roughness in granular flows. The geometric roughness of a base made of spheres is first characterized, with a wide range of particle size and packing arrangement (Jing et al., 2016).

  1. Jing, L., Kwok, C. Y., Leung, Y. F., & Sobral, Y. D. (2016). Characterization of base roughness for granular chute flows. Physical Review E, 94(5), 052901. https://doi.org/10.1103/PhysRevE.94.052901