Nugget

1
Instabilities in Granular Taylor-Couette Flow
Benjamin J. Glasser, Department of Chemical
Biochemical Engineering, Rutgers University,
Piscataway, NJ 08854
Understanding of many aspects of particulate
processing operations is important for the
petroleum industry. At the same time, granular
processes are often afflicted by poor performance
due to erratic flow, density waves, jamming,
undesired segregation, and structural failure. In
fluids, analysis of paradigmatic or model
experiments, like Benard, Couette,
Taylor-Couette, and Kelvin-Helmholtz, has served
to uncover aspects of shear transmission that
have led to a better understanding of flows of
engineering importance. For granular flows, we
believe improved understanding will hinge on
analysis of analogous paradigmatic or model
experiments. The focus of this work is
Taylor-Couette flows which are one of the
simplest model geometries encompassing both shear
and boundary interactions essential ingredients
of practical flows. Taylor-Couette granular flow
is examined using a combination of experiments,
particle dynamic simulations (see figure below)
and continuum mechanics/kinetic theory. Our focus
is on instabilities leading to mesoscopic
variations in density and flow properties and
spatio-temporal structures. By determining the
nature and magnitude of these instabilities we
anticipate more reliable methods of scale-up and
assurance of process performance. Going beyond
steady states to investigate time-dependent flows
will also allow us to test and further develop
constitutive equations that describe granular
flows.
Instability formation in a Taylor-Couette shear
flow. a) Homogeneous flow obtained for a solids
fraction of ? 0.15, and a high coefficient of
restitution. b) Instability for a low coefficient
of restitution. c) Instability for a high rolling
friction coefficient. d) Instability for a solids
fraction, ? 0.05. Particles are colored
according to their translational velocity.