Effects of non-uniform rheology on the motion of bubbles in a yield-stress fluid

Zare, M.; Daneshi, Masoud; Frigaard, I.A.

doi:10.1017/jfm.2021.326

Cited by 13 publications

(9 citation statements)

References 34 publications

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“…Ohta et al. 2005; Zhang, Yang & Mao 2010; Zare, Daneshi & Frigaard 2021). Following the earlier studies, to demonstrate the effect of the oscillation amplitude on the shear-thinning viscosity, figure 4 visualizes the distribution of the time-averaged viscosity around the bubble at .…”

Section: Simulation Resultsmentioning

confidence: 99%

Drag force on an oscillatory spherical bubble in shear‐thinning fluid

2023

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Power-law shear-thinning fluid motions induced by a translating spherical bubble with sinusoidal oscillation at a high frequency are numerically studied. We focus on reducing the time-averaged drag force $D$ on the bubble owing to the oscillation-enhanced shear-thinning effect. Under the assumption of negligible convection, the unsteady Stokes equation is directly solved in a finite-difference manner over a wide parameter space of the dimensionless oscillation amplitude $A$ (corresponding to the oscillatory-to-translational velocity ratio) and the power-law index $n$ of the viscosity. The results show that, for small amplitude ( $A\ll 1$ ), the drag reduction ratio $1-D/D_0$ (here, $D_0$ is $D$ with no oscillation) is proportional to $A^2$ . In contrast, for large amplitude ( $A \gg 1$ ), the drag ratio $D/D_0$ is proportional to $A^{n-1}$ , revealing a power-law behaviour. In the case of $A \gg 1$ for a strong shear-thinning fluid with small $n$ , the square of the vorticity over the entire domain is much smaller than that of the shear rate, and thus the bulk flow may be regarded as irrotational. To provide a fundamental perspective on the drag reduction mechanism, a theoretical model is proposed based on potential theory, and demonstrated to well capture the power-law relation between $D/D_0$ and $A$ .

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Section: Simulation Resultsmentioning

confidence: 99%

Drag force on an oscillatory spherical bubble in shear‐thinning fluid

2023

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“…Memory effects (believed viscoelastic), can strongly affect the path taken by successive bubbles, by changing the local rheology and/or residual stress distributions (Dubash & Frigaard 2007; Lopez et al. 2018; Zare, Daneshi & Frigaard 2021).…”

Section: Methodsmentioning

confidence: 99%

Growth and stability of bubbles in a yield stress fluid

Daneshi

Frigaard

2023

J. Fluid Mech.

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Experiments are reported that explore the onset of motion of bubbles in a model yield stress fluid, Carbopol gel. Starting from a trapped spherical bubble in a gel, the yielding limit for the bubble motion is obtained by gradually expanding the bubble via a stepwise decrease in pressure. Our results show that at the yielding limit bubbles are longer and thinner when they are in a higher concentrated gel. This is suggestive of a link between the shape and size of the bubbles at the onset of motion and the rheology of the material, in particular elastic behaviour below the yielding point. Particular attention has been paid to investigating the dynamic response of gel during the bubble growth. Subjecting the bubble to a periodic change in the pressure confirms the irreversibility of the gel deformation and its hysteresis, which are hallmarks of nonlinear viscoelastic behaviour of the gel before yielding. In this context, the periodic expansion and contraction of the bubbles leave residual deformation (stresses) in the gel which facilitates the liberation of bubbles.

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“…Specifically, Karapetsas et al. (2019) predicted that bubbles rise rapidly when excited at resonance, Zare, Daneshi & Frigaard (2021) have examined the propensity of bubbles to follow each other in pathways, and Pourzahedi et al. (2022) have examined the effect of shape on the onset of bubble motion.…”

Section: Introductionmentioning

confidence: 99%

The motion of a layer of yield-stress material on an oscillating plate

2023

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The motion of a finite layer of Bingham material on a solid plate that executes in-plane oscillations was reported previously by Balmforth et al. (J. Non-Newtonian Fluid Mech., vol. 158, issue 1–3, 2009, pp. 46–53). There, it was suggested that multiple yielded regions may arise within the material; this contrasts to start-up flow of the same material for which only one yielded region is generated. Here, we explore quantitatively the fluid physics of this oscillatory flow problem through analytical approximations and further numerical computation. Four new key topological properties concerning the generation and termination of the yielded regions are reported. It is shown that the existence of multiple yielded regions is equivalent to the layer never becoming entirely rigid during the periodic motion. For small inertia, the flow is approximately time-reversible with only a single yielded region generated at the plate. For large inertia, shear stress in the material decays rapidly as a function of distance from the plate. A thin zone of yielded material detaches periodically from the plate, and subsequently terminates within the layer. At high oscillation frequency, there can be any number $N$ of distinct rigid regions, satisfying $N= \lfloor 1- {\rm \pi}^{-1} \log B \rfloor$ where $B$ is the Bingham number. It is also shown that for $B>0.5370$ , there are at most one yielded region and one rigid region throughout the motion. These theoretical results can be used as a basis for oscillatory rheometry, allowing for measurement of the yield stress using existing apparatus.

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Effects of non-uniform rheology on the motion of bubbles in a yield-stress fluid

Abstract: Abstract

Cited by 13 publications

References 34 publications

Drag force on an oscillatory spherical bubble in shear‐thinning fluid

Drag force on an oscillatory spherical bubble in shear‐thinning fluid

Growth and stability of bubbles in a yield stress fluid

The motion of a layer of yield-stress material on an oscillating plate

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