Numerical Simulation of Bingham Plastics in a Squeeze-Flow Plastometer
Evan Mitsoulis, Andreas Matsoukas
NTUA
Greece

Keywords: Bingham Plastics, Squeeze Flow, Squeeze Force

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Numerical simulations of a Bingham plastic have been undertaken for squeezing flow under creeping flow conditions. Two different geometries are used, an axisymmetric one, defined by two coaxial disks between which the Bingham plastic flows, and a planar one, defined by two parallel plates of infinite width. In the planar geometry, a two-dimensional flow is assumed as the third dimension is neglected. Different aspect ratios have been studied ranging from 0.01 to 1. The Bingham constitutive equation is used with an appropriate modification proposed by Papanastasiou, which applies everywhere in the flow field in both yielded and practically unyielded regions. The emphasis is on determining the extent and shape of yielded / unyielded regions for a wide range of Bingham numbers in axisymmetric and planar geometries. The unyielded regions are very small and confined only near the center of the disks/plates. Axisymmetric geometries give smaller unyielded regions than planar ones for the same Bingham number. Big aspect ratios give larger unyielded regions than small ones for the same Bingham number. The present results extend previous simulations for squeeze flow of Bingham plastics between circular disks and provide calculations of the squeeze force along disks or plates for different aspect ratios. They also provide the limiting disk (plate) separation, beyond which a viscoplastic material cannot be squeezed.