The Rolling Transition in a Granular Flow along a Rotating Wall

Area of Science:

• Physics of granular materials
• Computational fluid dynamics
• Particle mechanics

Background:

• Granular flow along rotating boundaries is crucial for particle spreading processes.
• Understanding the complex phases of granular flow, including compression and elongation, is essential.

Purpose of the Study:

• To investigate the flow dynamics of dry granular materials composed of spherical particles along a rotating boundary.
• To characterize the deformation rates and effective friction coefficient of the granular flow.
• To identify transitions in particle motion regimes based on friction coefficients.

Main Methods:

• Utilizing the discrete element method (DEM) for numerical simulation of granular flow.
• Analyzing the flow phases: compression, elongation, and independent particle motion.
• Defining and calculating an effective friction coefficient on a continuum scale.

Main Results:

• The granular flow exhibits complex deformation rates involving traction/compression and shear.
• A critical friction coefficient (μ*) was identified, beyond which the effective friction significantly decreases.
• A novel 'rolling transition' was observed, shifting from sliding to rolling without sliding, controlled by particle-wall friction.

Conclusions:

• The spherical particle shape appears optimal for energy-efficient granular flow.
• The rolling transition is a key dynamic phenomenon controlled by particle-wall friction.
• Effective friction coefficient is a critical parameter for understanding and controlling granular flow behavior.