Author:
BERGENHOLTZ J.,BRADY J. F.,VICIC M.
Abstract
The non-Newtonian rheology is calculated numerically to second order in the volume
fraction in steady simple shear flows for Brownian hard spheres in the presence of
hydrodynamic and excluded volume interactions. Previous analytical and numerical
results for the low-shear structure and rheology are confirmed, demonstrating that
the viscosity shear thins proportional to Pe2, where Pe is the dimensionless shear rate
or Péclet number, owing to the decreasing contribution of Brownian forces to the
viscosity. In the large Pe limit, remnants of Brownian diffusion balance convection
in a boundary-layer in the compressive region of the flow. In consequence, the
viscosity shear thickens when this boundary-layer coincides with the near-contact
lubrication regime of the hydrodynamic interaction. Wakes are formed at large Pe
in the extensional zone downstream from the reference particle, leading to broken
symmetry in the pair correlation function. As a result of this asymmetry and that in
the boundary-layer, finite normal stress differences are obtained as well as positive
departures in the generalized osmotic pressure from its equilibrium value. The first
normal stress difference changes from positive to negative values as Pe is increased
when the hard-sphere limit is approached. This unusual effect is caused by the
hydrodynamic lubrication forces that maintain particles in close proximity well into
the extensional quadrant of the flow. The study demonstrates that many of the
non-Newtonian effects observed in concentrated suspensions by experiments and by
Stokesian dynamics simulations are present also in dilute suspensions.
Publisher
Cambridge University Press (CUP)
Subject
Mechanical Engineering,Mechanics of Materials,Condensed Matter Physics
Cited by
205 articles.
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