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Rheology of surface granular flows

DSpace at IIT Bombay

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Field Value
 
Title Rheology of surface granular flows
 
Creator ORPE, AV
KHAKHAR, DV
 
Subject shear flows
model
avalanches
dynamics
mixtures
grain
layer
 
Description Surface granular flow, comprising granular material flowing on the surface of a heap of the same material, occurs in several industrial and natural systems. The rheology of such a flow was investigated by means of measurements of velocity and number-density profiles in a quasi-two-dimensional rotating cylinder, half-filled with a model granular material - monosize spherical stainless-steel particles. The measurements were made at the Centre of the cylinder, where the flow is fully developed, using streakline photography and image analysis. The stress profile was computed from the number-density profile using a force balance which takes into account wall friction. Mean-velocity and root-mean-square (r.m.s.)-velocity profiles are reported for different particle sizes and cylinder rotation speeds. The profiles for the mean velocity superimpose when distance is scaled by the particle diameter d and velocity by a characteristic shear rate gamma(C) = [g sin(beta(m) - beta(s))/d cos beta(s)]1/2 and the particle diameter, where beta(m) is the maximum dynamic angle of repose and beta(s) is the static angle of repose. The maximum dynamic angle of repose is found to vary with the local flow rate. The scaling is also found to work for the r.m.s. velocity profiles. The mean velocity is found to decay exponentially with depth in the bed, with decay length lambda = 1.1d. The r.m.s. velocity shows similar behaviour but with lambda = 1.7d. The r.m.s. velocity profile shows two regimes: near the free surface the r.m.s. velocity is nearly constant and below a transition point it decays linearly with depth. The shear rate, obtained by numerical differentiation of the velocity profile, is not constant anywhere in the layer and has a maximum which occurs at the same depth as the transition in the r.m.s. velocity profile. Above the transition point the velocity distributions are Gaussian and below the transition point the velocity distributions gradually approach a Poisson distribution. The shear stress increases roughly linearly with depth. The variation in the apparent viscosity eta with r.m.s. velocity u shows a relatively sharp transition at the shear-rate maximum, and in the region below this point the apparent viscosity eta similar to u(-1.5). The measurements indicate that the flow comprises two layers: an upper low-viscosity layer with a nearly constant r.m.s. velocity and a lower layer of increasing viscosity with a decreasing r.m.s. velocity. The thickness of the upper layer depends on the local flow rate and is independent of particle diameter while the reverse is found to hold for the lower-layer thickness. The experimental data is compared with the predictions of three models for granular flow.
 
Publisher CAMBRIDGE UNIV PRESS
 
Date 2011-07-19T10:49:09Z
2011-12-26T12:51:10Z
2011-12-27T05:37:37Z
2011-07-19T10:49:09Z
2011-12-26T12:51:10Z
2011-12-27T05:37:37Z
2007
 
Type Article
 
Identifier JOURNAL OF FLUID MECHANICS, 571(), 1-32
0022-1120
http://dx.doi.org/10.1017/S002211200600320X
http://dspace.library.iitb.ac.in/xmlui/handle/10054/5272
http://hdl.handle.net/10054/5272
 
Language en