Continuum modeling of size-segregation and flow in dense, bidisperse
granular media: Accounting for segregation driven by both pressure gradients
and shear-strain-rate gradients
Dense mixtures of particles of varying size tend to segregate based on size
during flow. Granular size-segregation plays an important role in many
industrial and geophysical processes, but the development of coupled, continuum
models capable of predicting the evolution of segregation dynamics and flow
fields in dense granular media across different geometries has remained a
longstanding challenge. One reason is because size-segregation stems from two
driving forces: (1) pressure gradients and (2) shear-strain-rate gradients.
Another reason is due to the challenge of integrating segregation models with
rheological constitutive equations for dense granular flow. In this paper, we
build upon our prior work, which combined a model for
shear-strain-rate-gradient-driven segregation with a nonlocal continuum model
for dense granular flow rheology, and append a model for
pressure-gradient-driven segregation. We perform discrete element method (DEM)
simulations of dense flow of bidisperse granular systems in two flow
geometries, in which both segregation driving forces are present: namely,
inclined plane flow and planar shear flow with gravity. Steady-state DEM data
from inclined plane flow is used to determine the dimensionless material
parameters in the pressure-gradient-driven segregation model for both spheres
and disks. Then, predictions of the coupled, continuum model accounting for
both driving forces are tested against DEM simulation results across different
cases of both inclined plane flow and planar shear flow with gravity, while
varying parameters such as the size of the flow geometry, the driving
conditions of flow, and the initial conditions. Overall, we find that it is
crucial to account for both driving forces to capture segregation dynamics in
dense, bidisperse granular media across both flow geometries with a single set
of parameters.Comment: 25 pages with 9 figure