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Shear Banding in 4:1 Planar Contraction.

Soroush Hooshyar1, Natalie Germann2

  • 1Fluid Dynamics of Complex Biosystems, School of Life Sciences Weihenstephan, Technical University of Munich, 85354 Freising, Germany. soroush.hooshyar@tum.de.

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Summary

This study introduces a two-fluid model to simulate shear banding in polymer solutions, revealing how stress-induced migration causes localized flow regions and competes with recirculation in contraction flows.

Keywords:
contraction flownonequilibrium thermodynamicspolymer solutionsshear bandingtwo-fluid model

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Area of Science:

  • Polymer physics
  • Non-equilibrium thermodynamics
  • Computational fluid dynamics

Background:

  • Shear banding in entangled polymer solutions is a complex phenomenon impacting material properties.
  • Understanding the interplay between viscoelastic stress and polymer concentration is crucial.
  • Existing models often struggle to capture the localized nature of shear bands.

Purpose of the Study:

  • To develop and validate a two-fluid model for simulating shear banding in semidilute entangled polymer solutions.
  • To investigate the mechanism of stress-induced migration as the trigger for shear banding.
  • To analyze the competition between shear banding and flow recirculation in a planar contraction flow.

Main Methods:

  • Utilized a novel two-fluid model based on the generalized bracket approach of non-equilibrium thermodynamics.
  • Employed the OpenFOAM software package with the RheoTool v.2.0 viscoelastic solver.
  • Implemented the CUBISTA scheme for convection terms and the SIMPLEC algorithm for solving governing equations.

Main Results:

  • Successfully simulated shear banding, first observed downstream of the contraction.
  • Observed a transition from parabolic to plug-like velocity profiles post-contraction.
  • Demonstrated that shear banding competes with flow recirculation, consistent with experimental data.
  • Polymer concentration profiles showed a peak in shear banding regions, shifting towards the channel center with increased velocity.

Conclusions:

  • The developed two-fluid model accurately captures shear banding phenomena in polymer solutions.
  • Stress-induced migration is confirmed as a key mechanism driving shear banding.
  • The model's capability to simulate localized shear bands has significant implications for industrial applications.