Granular flow

Granular flow is the collective motion of many discrete solid particles under gravity, applied forces, or imposed motion. Its behavior can resemble that of a solid, liquid, or gas depending on conditions.

Granular temperature: A measure of random particle motion in a granular material, defined from velocity fluctuations. It describes agitation that helps distinguish dense flow from gas-like particle motion.
Hopper: A container with a downward outlet used to store and discharge bulk solids. Its outlet flow and arch formation are central engineering problems for granular materials.
Granular material: A collection of discrete solid particles large enough that thermal motion is negligible. Granular flow is the moving state of this broader class of materials.
Newtonian fluid: A fluid whose shear stress is proportional to its rate of deformation, with constant viscosity. Granular flow can change resistance with packing and stress, unlike this standard fluid model.
Jamming: A transition in which a disordered material becomes mechanically rigid as its particles become constrained. Granular flow can stop abruptly when contacts form a load-bearing network.
Silo: A tall structure for storing bulk materials such as grain, cement, or coal. Grain discharge and wall loads depend on how particles flow and jam.
Friction: Resistance to relative motion between contacting surfaces. Grain friction controls resistance to sliding and the stability of piles.
Non-Newtonian fluid: A fluid whose viscosity or stress response depends on deformation rate or history. Some dense granular flows resemble these fluids but retain discrete solid contacts.
Shear band: A narrow region in a material where most deformation is concentrated. Granular shear often localizes into thin bands instead of spreading uniformly.
Granular segregation: The separation of particles in a mixture by size, density, or other properties during motion. Flow can sort mixed grains and undermine uniformity in industrial products.

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