Publications
Profile blunting and flow blockage in a yield stress fluid: A molecular dynamics study
F. Varnik, D. Raabe.
Physical Review E, The American Physical Society, 77, 011504, 1-9, (2008)
Abstract
The flow of a simple glass forming system (a 80:20 binary Lennard-Jones mixture) through a
planar channel is studied via molecular dynamics simulations. The flow is driven by an external
body force similar to gravity. Previous studies show that the model exhibits both a static [Varnik
et al. J. Chem. Phys. 120, 2788 (2004)] and a dynamic [F. Varnik and O. Henrich Phys. Rev.
B 73, 174209 (2006)] yield stress in the glassy phase. These observations are corroborated by the
present work, where we investigate how the presence of a yield stress may affect the system behavior
in a Poiseuille-type flow geometry. In particular, we observe a blunted velocity profile across the
channel: A relatively wide region in the channel center flows with a constant velocity (zero shear
rate) followed by a non linear change of the shear rate as the walls are approached. The observed
velocity gradients are compared to those obtained from the knowledge of the shear stress across the
channel and the flow-curves (stress versus shear rate), the latter being determined in our previous
simulations of homogeneous shear flow. Furthermore, using the value of the (dynamic) yield stress
known from previous simulations, we estimate the threshold body force for a complete arrest of the
flow. Indeed, a blockage is observed as the imposed force falls below this threshold value. Small but
finite shear rates are observed at stresses above the dynamic but below the static yield stress. We
discuss the possible role of the stick-slip like motion for this observation.
Keyword(s): Glass transition, Molecular dynamics method, Poiseuille flow, Yield stress
DOI: 10.1103/PhysRevE.77.011504
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