Heaps of sand in flows within a split-bottom Couette cell

Area of Science:

• Physics of granular materials
• Fluid dynamics of non-spherical particles

Background:

• Angular grains, unlike spherical ones, exhibit complex collective flow fields forming heaps on free surfaces.
• Previous studies in split-bottom cells noted specific flow behaviors, but a wider range, especially within the inertial regime, remained unexplored.

Purpose of the Study:

• To investigate the flow dynamics of angular grains in a split-bottom Couette cell across a broader range of inertial flows.
• To characterize the resulting heap morphology and flow regimes.
• To extend the understanding of universal shear banding and free-surface deformations.

Main Methods:

• Utilizing a split-bottom Couette cell to study angular grain flow.
• Employing digital image analysis to accurately measure surface height and velocity profiles.
• Exploring flows within the inertial regime and varying confinement levels.

Main Results:

• Observed known flow regimes (universal, wall-collapsed) persisting in moderately high inertial flows.
• Demonstrated that heap morphology is amplified by flow inertia and partially collapses upon halting.
• Identified distinct flow behaviors at high angular velocities: radial spreading under low confinement and localized particle ejections under high confinement.

Conclusions:

• The study extends the range for observing universal shear banding in granular flows.
• Results highlight the significant impact of flow inertia on heap morphology and free-surface deformation.
• Findings suggest the necessity of incorporating deformable free-surface boundary conditions in simulations of angular grain shear flows for accurate prediction of natural mass flows.