Mono-layer Granular Poiseuille Flow
-------- rolling spheres on a smooth incline
"Two-dimensional granular Poiseuille Flow on an
incline: multiple dynamical regimes", J-C
Tsai, W. Losert, G.A. Voth, and J.P. Gollub, Phys.
Rev. E 65, 011306 (2002).
We investigate experimentally
the flow of a monolayer of spherical beads through a channel on a smooth
incline that is bounded by rough sidewalls. Using high speed video
imaging and particle tracking, we measure the positions and velocities
of all particles in the field of view. We find that the flows are accelerating
and dilute if the channel exit is open. On the other hand, if the exit
is constricted, flows can reach a state in which the local time-averaged
velocity is invariant along the stream. In the latter case, we find a
continuous transition from an oscillatorytwo-phase flow (2PF) regime with
wide density variations to a uniform dense flow (UDF) regime, depending
on the channel width and the mean flow speed. These two regimes exhibit
distinct density variation, time regularity, and transverse profiles.
The rough sidewalls are found to be necessary for the 2PF regime. In the
dense regions of both flows, particles exhibit temporary arches, long-range
correlated velocities, inhomogenuous propagation of disturbances, and
hexagonal lattice structures. On the other hand, the dilute regions of
the two-phase flow are nearly collisionless. Existing models cannot fully
describe the dynamics of both the dense and the dilute regions, or explain
the spontaneous switching between them.