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PURELY ELASTIC FLOW ASYMMETRIES IN CROSS-SLOT GEOMETRY - ARE THEY ALWAYS PRESENT?

DOI: 10.1615/ICHMT.2012.CHT-12.290
pages 471-485

A. Filali
Department of Mechanical Engineering, Petroleum Institute, Abu Dhabi, United Arab Emirates

Lyes Khezzar
Mechanical Engineering Department, The Petroleum Institute, P.O. Box 2533, Abu Dhabi, United Arab Emirates

Fernando T. Pinho
CEFT, Department of Mechanical Engineering, Faculty of Engineering University of Porto, 4200-465, Porto, Portugal

M. A. Alves
Department of Chemical Engineering, CEFT, Faculty of Engineering, University of Porto, 4200-465, Porto, Portugal

Abstract

Numerical investigations of purely-elastic instabilities occurring in creeping flows (Re ≈ 0) are reported in planar cross-slot geometries with both Sharp and Round corners. The fluid is described by the Upper-Convected Maxwell (UCM) model, and the governing equations are solved using the finite element technique in the POLYFLOW code. The calculations performed show that the onset of flow asymmetries above a critical Deborah number is extremely sensitive to the numerical characteristics. Specifically, extensive simulations were carried out on symmetric and distorted meshes for a wide range of rheological parameters showing that for asymmetric meshes and above a critical Deborah number Decr, the flow becomes asymmetric, but remains steady. The effect of rounding the corners is also addressed. When the flow becomes asymmetric, the numerical results obtained are found to be in good quantitative agreement with previously published numerical results that include velocity profiles, stream function, variation of Weissenberg number with De and flow asymmetry parameter.

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