Segregation induced instabilities of granular fronts

Area of Science:

• Physics of granular materials
• Fluid dynamics
• Geophysics

Background:

• Granular flows on slopes are common in nature and industry.
• Particle segregation significantly influences flow behavior and front dynamics.
• Understanding instabilities is crucial for predicting and mitigating granular avalanches.

Purpose of the Study:

• To investigate the fingering instability in granular flows with mixed particle sizes.
• To elucidate the mechanisms of particle size segregation driving the instability.
• To develop a predictive model for flow instabilities.

Main Methods:

• Experimental investigation of granular flows on slopes with varying particle sizes.
• Analysis of particle migration and velocity profiles.
• Development and application of a simple analytical model.

Main Results:

• Size segregation of coarse, irregular particles induces fingering instability at the flow front.
• Small particles percolate down, while large particles migrate to the surface and front.
• Instability in dry flows depends on angularity and increased friction of large perimeter particles.
• Viscous liquid presence inhibits segregation and instability.
• Fluidization of dry flows can lead to similar instabilities.

Conclusions:

• Particle size segregation is a key driver of fingering instability in granular flows.
• Flow front friction exceeding internal friction predicts instability.
• The presence of liquid or fluidization alters segregation and instability dynamics.