Influence of channel aspect ratio on the onset of purely-elastic flow instabilities in three-dimensional planar cross-slots

Cruz, FA, Poole, RJ ORCID: 0000-0001-6686-4301, Afonso, AM, Pinho, FT, Oliveira, PJ and Alves, MA (2016) Influence of channel aspect ratio on the onset of purely-elastic flow instabilities in three-dimensional planar cross-slots. JOURNAL OF NON-NEWTONIAN FLUID MECHANICS, 227. pp. 65-79.

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Official URL: http://dx.doi.org/10.1016/j.jnnfm.2015.11.008

Abstract

In this work, we perform creeping-flow simulations of upper-convected Maxwell and simplified Phan-Thien-Tanner fluids to study the purely-elastic steady bifurcation and transition to time-dependent flow in three-dimensional planar cross-slots. By analysing the flow in geometries with aspect ratios ranging from the near Hele-Shaw flow like limit, up to the very deep, two-dimensional limit, we are able to characterize the mechanism of the cross-slot bifurcation with significant detail. We conclude that the bifurcation mechanism is similar to a buckling instability, by which fluid is redirected via paths of least resistance, resulting in the emergence of peripheral stagnation points, above and below the central stagnation point. The intake of matter at the centre via the inlet axis is thus reduced, being compensated by fluid flowing through low resistance corridors along the central vertical axis, above and below the central point. Furthermore, we propose and locally compute a modified Pakdel-McKinley criterion, thereby producing a scalar stability field and suggesting emergent peripheral stagnation points also indirectly contribute to the onset of time-dependent flow.

Item Type:	Article
Uncontrolled Keywords:	Finite-volume method, Cross-slot flow, Elastic instability, Stagnation-point flow, Steady flow bifurcation, Modified Pakdel-McKinley criterion
Depositing User:	Symplectic Admin
Date Deposited:	12 Apr 2016 11:17
Last Modified:	15 Dec 2022 16:25
DOI:	10.1016/j.jnnfm.2015.11.008
Related URLs:	Author Publisher
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3000437