TY - JOUR
T1 - Creeping granular motion under variable gravity levels
AU - Arndt, Tim
AU - Brucks, Antje
AU - Ottino, Julio M.
AU - Lueptow, Richard M.
PY - 2006
Y1 - 2006
N2 - In a rotating tumbler that is more than one-half filled with a granular material, a core of material forms that should ideally rotate with the tumbler. However, the core rotates slightly faster than the tumbler (precession) and decreases in size (erosion). The precession and erosion of the core provide a measure of the creeping granular motion that occurs beneath a continuously flowing flat surface layer. Since the effect of gravity on the subsurface flow has not been explored, experiments were performed in a 63% to 83% full granular tumbler mounted in a large centrifuge that can provide very high g -levels. Two colors of 0.5 mm glass beads were filled side by side to mark a vertical line in the 45 mm radius quasi-two-dimensional tumbler. The rotation of the core with respect to the tumbler (precession) and the decrease in the size of the core (erosion) were monitored over 250 tumbler revolutions at accelerations between 1g and 12g. The flowing layer thickness is essentially independent of the g -level for identical Froude numbers, and the shear rate in the flowing layer increases with increasing g -level. The degree of core precession increases with the g -level, while the core erosion is essentially independent of the g -level. Based on a theory for core precession and erosion, the increased precession is likely a consequence of the higher shear rate. Core erosion, on the other hand, is related to the creep region decay constant, which is connected with slow diffusion in the bed and unaffected by gravity.
AB - In a rotating tumbler that is more than one-half filled with a granular material, a core of material forms that should ideally rotate with the tumbler. However, the core rotates slightly faster than the tumbler (precession) and decreases in size (erosion). The precession and erosion of the core provide a measure of the creeping granular motion that occurs beneath a continuously flowing flat surface layer. Since the effect of gravity on the subsurface flow has not been explored, experiments were performed in a 63% to 83% full granular tumbler mounted in a large centrifuge that can provide very high g -levels. Two colors of 0.5 mm glass beads were filled side by side to mark a vertical line in the 45 mm radius quasi-two-dimensional tumbler. The rotation of the core with respect to the tumbler (precession) and the decrease in the size of the core (erosion) were monitored over 250 tumbler revolutions at accelerations between 1g and 12g. The flowing layer thickness is essentially independent of the g -level for identical Froude numbers, and the shear rate in the flowing layer increases with increasing g -level. The degree of core precession increases with the g -level, while the core erosion is essentially independent of the g -level. Based on a theory for core precession and erosion, the increased precession is likely a consequence of the higher shear rate. Core erosion, on the other hand, is related to the creep region decay constant, which is connected with slow diffusion in the bed and unaffected by gravity.
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U2 - 10.1103/PhysRevE.74.031307
DO - 10.1103/PhysRevE.74.031307
M3 - Article
C2 - 17025623
AN - SCOPUS:33748957315
SN - 1539-3755
VL - 74
JO - Physical Review E - Statistical, Nonlinear, and Soft Matter Physics
JF - Physical Review E - Statistical, Nonlinear, and Soft Matter Physics
IS - 3
M1 - 031307
ER -