Structural features in granular flows

Journal Article · Sun Jun 10 00:00:00 EDT 1990 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JB095iB06p08681· OSTI ID:5073592

Drake, T G ^[1]

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1. Univ. of California, Los Angeles (United States)

High-speed motion pictures document a series of essentially two-dimensional, free-surface flows of 6-mm diameter plastic spheres generated in an inclined glass-walled chute 3.7 m long and 6.7 mm wide. Flows at sufficiently low inclination or high particle flux can generally be divided into frictional and collisional regions. The frictional region typically consists of a quasi-static zone extending up from the fixed bed and an overlying block-gliding zone, in which coherent blocks of grains move parallel to the bed. The collisional region overlies the contact region in sufficiently deep flows; otherwise it extends to the bed. It typically consists of three zones: a lower grain-layer-gliding zone, in which grains appear to slide over one another; a middle chaotic zone, in which grain motions are highly random, as in a dense gas; and an overlying saltational zone, in which grains trace long, curved paths. In none of the flows does a frictional region overlie a collisional region. Zone thicknesses and block dimensions are previously unrecognized length scales in granular flows. The no-slip velocity boundary condition applies only when a frictional region adjoins a geometrically rough fixed bed, otherwise significant slip occurs (up to 50% of the mean flow velocity). Because many collision-dominated geophysical flows start from friction-dominated ones and end by reverting to the frictional regime as the energy supply diminishes, kinetic theories of granular flow, which unanimously employ the binary-collision assumption, can at best describe only a portion of the phenomena. Microstructural descriptions of the relatively slow, compact, and frictional regions evident in most geophysical flows are required to complement existing kinetic theories.

• OSTI ID: 5073592
• Journal Information: Journal of Geophysical Research; (United States), Vol. 95:B6; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
GRANULAR MATERIALS
SOLIDS FLOW
BOUNDARY CONDITIONS
ENVIRONMENTAL TRANSPORT
FLOW VISUALIZATION
FLUIDIZED BEDS
FRICTION FACTOR
GEOPHYSICS
LANDSLIDES
MICROSTRUCTURE
MOTION
PACKED BED
PLASTICS
RINGS
RIVERS
SATURN PLANET
SEDIMENTS
SLURRY PIPELINES
SPHERES
STRATIFICATION
THICKNESS
TWO-DIMENSIONAL CALCULATIONS
ULTRAHIGH-SPEED PHOTOGRAPHY
CRYSTAL STRUCTURE
DIMENSIONS
FLUID FLOW
FREIGHT PIPELINES
MASS TRANSFER
MATERIALS
PETROCHEMICALS
PETROLEUM PRODUCTS
PHOTOGRAPHY
PIPELINES
PLANETS
STREAMS
SURFACE WATERS
SYNTHETIC MATERIALS
580000* - Geosciences