Experimental study of granular flows in a rough annular shear cell

Area of Science:

• Physics
• Rheology
• Granular Mechanics

Background:

• Granular flows are prevalent in nature and industry but challenging to model due to nonlinear, multiphase behavior.
• Previous experiments provided insights, but the effect of surface roughness on local flow dynamics remained less understood.
• Understanding granular flow-surface interactions has implications for industrial processes and phenomena like wheel-terrain interaction.

Purpose of the Study:

• To investigate the influence of surface roughness on the local flow behavior of granular materials.
• To experimentally quantify the relationship between wall roughness, rotation rate, and granular flow characteristics.
• To analyze the phenomenon of slip at the interface between granular material and a moving rough surface.

Main Methods:

• Development of a two-dimensional annular shear cell to conduct controlled shear experiments.
• Imposition and experimental quantification of roughness on the driving surface of the shear cell.
• Utilization of digital particle tracking velocimetry (PTV) to extract solid fraction, velocity, and granular temperature data.

Main Results:

• Observed two distinct flow regions: a dilute, gas-like kinetic region near the wall and a dense, liquid-like frictional regime further away.
• Demonstrated that normalized slip near the moving wall decreases as wall roughness increases and wall rotation rate decreases.
• Quantified granular temperature and solid fraction variations in relation to roughness and rotation.

Conclusions:

• Wall roughness significantly modifies the slip behavior at the granular-wall interface.
• Decreased slip with increased roughness suggests reduced momentum transfer or traction, relevant for granular lubrication and wheel-terrain applications.
• The developed experimental setup and PTV scheme provide a robust method for studying granular flow-surface interactions.