Author:
BUTLER JASON E.,SHAQFEH ERIC S. G.
Abstract
We have simulated the dynamics of suspensions of fibres sedimenting in the limit of
zero Reynolds number. In these simulations, the dominant inter-particle force arises
from hydrodynamic interactions between the rigid, non-Brownian fibres. The simulation algorithm uses slender-body theory to model the linear and rotational velocities
of each fibre. To include far-field interactions between the fibres, the line distribution
of force on each fibre is approximated by making a Legendre polynomial expansion of
the disturbance velocity on the fibre, where only the first two terms of the expansion
are retained in the calculation. Thus, the resulting linear force distribution can be
specified completely by a centre-of-mass force, a couple, and a stresslet. Short-range
interactions between particles are included using a lubrication approximation, and an
infinite suspension is simulated by using periodic boundary conditions. Our numerical results confirm that the sedimentation of these non-spherical, orientable particles
differs qualitatively from the sedimentation of spherical particles. The simulations
demonstrate that an initially homogeneous, settling suspension develops clusters,
or streamers, which are particle rich surrounded by clarified fluid. The instability
which causes the heterogeneous structure arises solely from hydrodynamic interactions which couple the particle orientation and the sedimentation rate in particle
clusters. Depending upon the concentration and aspect ratio, the formation of clusters of particles can enhance the sedimentation rate of the suspension to a value in
excess of the maximum settling speed of an isolated particle. The suspension of fibres
tends to orient with gravity during the sedimentation process. The average velocities
and orientations, as well as their distributions, compare favourably with previous
experimental measurements.
Publisher
Cambridge University Press (CUP)
Subject
Mechanical Engineering,Mechanics of Materials,Condensed Matter Physics
Cited by
98 articles.
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