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| 2003-2004 Fluids Seminar Page |
Abstract-
Particles moving through a viscous fluid interact with
each other, because
each individual particle drags fluid along with it, which then pulls on
other particles. In a low Reynolds number sediment, such hydrodynamic
interactions are extremely strong, even when the particles are well
separated.
The character of the particle motions in a dilute suspension of heavy
particles is still highly
controversial: In 1985, Caflisch and Luke presented an extremely simple
argument indicating that the velocity fluctuations in such a sediment
should diverge with the system size. Experiments have mainly contradicted
this conclusion, leading to the hope that there is a (perhaps universal)
''screening mechanism'' controlling the size of the fluctuations. In this
lecture I will review the history of this problem, and then present the
results of our recent research which indicates that the velocity
fluctuations are highly nonuniversal and system size dependent, depending
subtley on both the shape of the container holding the sediment and any
particle stratification that develops during an experiment. Experiments,
numerical simulations and theory are presented that quantitatively support
this point of view.
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