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Predicting large experimental excess pressure drops for Boger fluids in contraction–expansion flow

I.E. Garduño, J.E. López-Aguilar, Michael Webster Orcid Logo, Hamid Tamaddon-Jahromi

Journal of Non-Newtonian Fluid Mechanics, Volume: 230, Pages: 43 - 67

Swansea University Authors: Michael Webster Orcid Logo, Hamid Tamaddon-Jahromi

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DOI (Published version): 10.1016/j.jnnfm.2016.01.019

Abstract

More recent finite element/volume studies on pressure-drops in contraction flows have introduced a variety of constitutive models to compare and contrast the competing influences of extensional viscosity, normal stress and shear-thinning. In this study, the ability of an extensional White–Metzner co...

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Published in: Journal of Non-Newtonian Fluid Mechanics
ISSN: 0377-0257
Published: 2016
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URI: https://cronfa.swan.ac.uk/Record/cronfa26430
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Abstract: More recent finite element/volume studies on pressure-drops in contraction flows have introduced a variety of constitutive models to compare and contrast the competing influences of extensional viscosity, normal stress and shear-thinning. In this study, the ability of an extensional White–Metzner construction with FENE-CR model is explored to reflect enhanced excess pressure drops (epd) in axisymmetric 4:1:4 contraction-expansion flows. Solvent-fraction is taken as =0.9, to mimic viscoelastic constant shear-viscosity Boger fluids. The experimental pressure-drop data of Rothstein & McKinley [1] has been quantitatively captured (in the initial pronounced rise with elasticity, and limiting plateau-patterns), via two modes of numerical prediction: (i) flow-rate Q-increase, and (ii) relaxation-time 1-increase. Here, the former Q-increase mode, in line with experimental procedures, has proved the more effective, generating significantly larger enhanced-epd. This is accompanied with dramatically enhanced trends with De-incrementation in vortex-activity, and significantly larger extrema in N1, shear-stress and related extensional and shear velocity-gradient components. In contrast, the 1-increase counterpart trends remain somewhat invariant to elasticity rise. Moreover, under Q-increase and with elasticity rise, a pattern of flow transition has been identified through three flow-phases in epd-data; (i) steady solutions for low-to-moderate elasticity levels, (ii) oscillatory solutions in the moderate elasticity regime (coinciding with Rothstein & McKinley [1] data), and (iii) finally solution divergence. New to this hybrid algorithmic formulation are - techniques in time discretisation, discrete treatment of pressure terms, compatible stress/velocity-gradient representation; handling ABS-correction in the constitutive equation, which provides consistent material-property prediction; and introducing purely-extensional velocity-gradient component specification at the shear-free centre flow-line through the velocity gradient (VGR) correction.
Keywords: Viscoelastic fluid; pressure-drop prediction; extensional White–Metzner_FENE-CR model; axisymmetric contraction-expansion
College: Faculty of Science and Engineering
Start Page: 43
End Page: 67

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