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Title: Modelling the nonlinear dynamics of polymer solutions in complex flows
Author: Omowunmi, Sunday Chima
ISNI:       0000 0004 2703 653X
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2011
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The flow of polymer solutions in the high Elasticity number, El, regime in complex geometries may lead to strong viscoelastic behaviour and eventually become unstable as the Weissenberg number, Wi, is increased beyond a critical level. So far, the success of numerical simulations in predicting the highly non-linear behaviour of polymer solutions in complex flows has been limited. In this thesis, selected constitutive models are evaluated under the high El flow regime in the cross-slot and contraction benchmark flows using a numerical technique based on the finite volume method. The numerical technique is implemented within the OpenFOAM framework and thoroughly validated in the benchmark flow. A modification to the FENE dumbbell model based on the non-affine deformation of polymer solutions is proposed, which enabled the prediction of some non-linear material functions and also enhanced numerical stability, allowing a higher Wi to be attained. Asymmetric flow instability in the cross-slot flow has been studied. Time-dependent stability diagrams were constructed based on Wi and the strain, ε, both of which govern the stretching of a polymer chain. In the contraction flow, elastic instability is simulated for the first time in this geometry. Substantial time-dependent asymmetric flow patterns were predicted as seen in experiments. The effect of the contraction ratio is investigated through a stability diagram. Three-dimensional finite element simulations were also carried out to study the effect of the aspect ratio in the contraction flow of a Phan-Thien-Tanner fluid. The simulations suggest that a lip vortex mechanism is a signature for the onset of strong viscoelastic behaviour.
Supervisor: Yuan, Xue-Feng Sponsor: Overseas Research Scholarship Award ; University of Manchester
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: nonlinear dynamics, FENE-CD-JS, viscoelastic flow, polymer solution, modelling, contraction flow, cross-slot flow, hydrodynamic drag, conformation dependent drag, non-affine deformation, elastic instability, asymmetric vortex, computational rheology