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Spatiotemporal Instabilities in Discontinuous Shear Thickening Fluids / PETER ANGERMAN

Swansea University Author: PETER ANGERMAN

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DOI (Published version): 10.23889/SUThesis.71080

Abstract

The aim of this work is to study instabilities and the formation of corollary patterns in order to gain a deeper understanding of the underlying physical phenomena and the conditions that lead to the chaotic behaviour of discontinuous shear thickening (DST) fluids. This work consists of two major sec...

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Published: Swansea 2025
Institution: Swansea University
Degree level: Doctoral
Degree name: Ph.D
Supervisor: Sandnes, B.
URI: https://cronfa.swan.ac.uk/Record/cronfa71080
Abstract: The aim of this work is to study instabilities and the formation of corollary patterns in order to gain a deeper understanding of the underlying physical phenomena and the conditions that lead to the chaotic behaviour of discontinuous shear thickening (DST) fluids. This work consists of two major sections, computational and experimental. In the computational sections, we focus on the problem of rheochaos and aim to develop a minimal microstructural model required to reproduce aperiodic oscillatory behaviour in simple shear. We begin by presenting the first microstructural implementation of DST in Smoothed Particle Hydrodynamics (SPH). We demonstrate that locality in microstructure evolution combined with the characteristic rheology of DST materials yields an inherent spatial instability. We introduce a non-local com-ponent in microstructure evolution to obtain formation of frictional structures with a well-defined length scale. Analysis of competition between local and non-local components allowed us to identify spatial configuration as a key feature required to obtain aperiodic solutions. By tuning the parameter space to closely resemble realistic DST materials, we are able to reproduce rheochaotic oscillations closely resembling those reported in the literature, driven by transient cycles of emergence and dissipation in localised frictional structures. Application to realistic flow geometries reveals excellent performance, with our model being able to capture the problem of flow curve construction, the effects of confinement and inertia, and instabilities in Poiseuille flow. Our experimental work focuses on free surface flows. We report a new ’ridge’ flow instability in the inclined plane arrangement and identify the significant negative values of N2 as the driving mechanism. By employing a combination of trough and inclined plane measurements, we demonstrate that the inclined plane is a plausible tool for measurement of N2 in regimes where conventional methods are not readily applicable.
Keywords: Computational Fluid Dynamics, Non-Newtonian Fluids, Rheology
College: Faculty of Science and Engineering
Funders: EPSRC Doctoral Training Grant (DTG)

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