Journal article 753 views
High-Weissenberg predictions for micellar fluids in contraction–expansion flows
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Hamid Tamaddon Jahromi
Journal of Non-Newtonian Fluid Mechanics, Volume: 222, Pages: 190 - 208
Swansea University Authors:
Michael Webster , Hamid Tamaddon Jahromi
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DOI (Published version): 10.1016/j.jnnfm.2014.11.008
Abstract
This study is concerned with the numerical modelling of thixotropic and non-thixotropic materials in contraction-expansion flows at high Weissenberg number (We). Thixotropy is represented via a new micellar time-dependent constitutive model for worm-like micellar systems and contrasted against netwo...
| Published in: | Journal of Non-Newtonian Fluid Mechanics |
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| ISSN: | 03770257 |
| Published: |
2015
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| Online Access: |
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| URI: | https://cronfa.swan.ac.uk/Record/cronfa24184 |
| Abstract: |
This study is concerned with the numerical modelling of thixotropic and non-thixotropic materials in contraction-expansion flows at high Weissenberg number (We). Thixotropy is represented via a new micellar time-dependent constitutive model for worm-like micellar systems and contrasted against network-based time-independent PTT forms. The work focuses on steady-state solutions in axisymmetric rounded-corner 4:1:4 contraction-expansion flows for the benchmark solvent-fraction of β=1/9 and moderate hardening characteristics (=0.25). In practice, this work has relevance to industrial and healthcare applications, such as enhanced oil-reservoir recovery and microfluidics. Simulations have been performed via a hybrid finite element/finite volume algorithm, based around an incremental pressure-correction time-stepping structure. To obtain high-We solutions, both micellar and PTT constitutive equation f-functionals have been amended by (i) adopting their absolute values appealing to physical arguments (ABS-correction); (ii) through a change of stress variable, Π=τp+(ηp0/λ1)I, that aims to prevent the loss of evolution in the underlying initial value problem; and finally, (iii) through an improved realisation of velocity gradient boundary conditions imposed at the centreline (VGR-correction). On the centreline, the eigenvalues of Π are identified with its Π–stress-components, and discontinuities in Π–components are located and associated with the f-functional-poles in simple uniaxial extension. Quality of solution is described through rz, N1 and N2 (signature of vortex dynamics) stress fields, and -eigenvalues. With {micellar, EPTT} fluids, the critical Weissenberg number is shifted from critical states of Wecrit={4.9, 220} without correction, to Wecrit={O(102), O(103)} with ABS-VGR-correction. Furthermore, such constitutive equation correction has been found to have general applicability. |
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| Keywords: |
high-elasticity solutions, positive definiteness, wormlike micelles, Bautista-Manero models, numerical simulation, hybrid finite element/volume method, enhanced oil-recovery |
| College: |
Faculty of Science and Engineering |
| Start Page: |
190 |
| End Page: |
208 |