The effects of viscoelasticity and shear thinning on the inertial instability and mixing performance in a T-channel geometry

Hill, RJ ORCID: 0000-0003-0114-2118, Davoodi, M ORCID: 0000-0002-1707-6453, Haward, SJ ORCID: 0000-0002-1884-4100, Fonte, CP ORCID: 0000-0001-9714-0779 and Poole, RJ ORCID: 0000-0001-6686-4301 (2026) The effects of viscoelasticity and shear thinning on the inertial instability and mixing performance in a T-channel geometry Journal of Non Newtonian Fluid Mechanics, 348. p. 105564. ISSN 0377-0257, 1873-2631

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Abstract

The T-channel, in which two opposing square inlet streams join and turn through 90° into a rectangular outlet of equal cross-sectional area, exhibits a steady symmetry-breaking bifurcation above a critical Reynolds number. For Newtonian fluids it is well-established that this transition produces engulfment flow and consequent enhanced mixing. However, the transition behaviour and mixing of viscoelastic and shear thinning fluids in the T-channel is less well studied or understood. In this work, finite-volume flow simulations are used to investigate how non-Newtonian rheology influences both the onset of instability and the resulting mixing performance. For constant-viscosity viscoelastic models, the Oldroyd-B fluid destabilises the flow, leading to transition at lower Reynolds numbers than in the Newtonian case, while the Oldroyd-A fluid stabilises the flow, delaying the onset of the engulfment regime. This contrast highlights the influence of normal stress differences on critical conditions. For shear-thinning Giesekus and Carreau models, the critical Reynolds number depends strongly on how the Reynolds number is defined; using the zero-shear viscosity both predict destabilisation relative to the Newtonian baseline. Analysis of the outlet channel shows that the instability mechanism is governed by the strength of secondary Dean-type vortices generated by the 90° turn, which are amplified or suppressed depending on the balance between inertia, curvature and rheology. Finally, the quantification of the mixing index reveals that, despite shifting the onset of instability, all non-Newtonian models studied reduce mixing efficiency of the mixer relative to the Newtonian case.

Item Type:	Article
Uncontrolled Keywords:	T-channel, Microfluidics, Viscoelastic, Shear-thinning, Inertial instability, Mixing
Divisions:	Faculty of Science & Engineering Faculty of Science & Engineering > School of Engineering Faculty of Science & Engineering > School of Engineering > Mechanical and Aerospace Engineering
Depositing User:	Symplectic Admin
Date Deposited:	16 Feb 2026 16:49
Last Modified:	03 Mar 2026 14:27
DOI:	10.1016/j.jnnfm.2026.105564
Open Access URL:	https://doi.org/10.1016/j.jnnfm.2026.105564
Related Websites:	Author Publisher
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3197050
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