| 1. |
- Ge, Zhouyang, et al.
(författare)
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Rheology of periodically sheared suspensions undergoing reversible-irreversible transition
- 2022
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Ingår i: Physical review. E. - : American Physical Society (APS). - 2470-0045 .- 2470-0053. ; 106:5
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Tidskriftsartikel (refereegranskat)abstract
- The rheology of noncolloidal suspensions under cyclic shear is studied numerically. The main findings are a strain amplitude (gamma 0) dependent response in the shear stress and second normal stress difference (N2). Specifically, we find a reduced viscosity, an enhanced intracycle shear thinning, the onset of a finite N2, and its frequency doubling, all near a critical strain amplitude gamma c that scales with the volume fraction 0 as gamma c similar to 0-2. These rheological changes also signify a reversible-irreversible transition (RIT), dividing stroboscopic particle dynamics into a reversible absorbing phase (for gamma 0 < gamma c) and a persistently diffusing phase (for gamma 0 > gamma c). We explain the results based on two flow-induced mechanisms and elucidate their connection in the context of RIT through the underlying microstructure, which tends toward hyperuniformity near gamma 0 = gamma c. Overall, we expect this correspondence between rheology and emergent dynamics to hold in a wide range of settings where structural organizations are dominated by volume exclusions.
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| 2. |
- Pietrzyk, Kyle, et al.
(författare)
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Flow around a squirmer in a shear-thinning fluid
- 2019
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Ingår i: Journal of Non-Newtonian Fluid Mechanics. - : Elsevier. - 0377-0257 .- 1873-2631. ; 268, s. 101-110
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Tidskriftsartikel (refereegranskat)abstract
- Many biological fluids display shear-thinning rheology, where the viscosity decreases with an increasing shear rate. To better understand how this non-Newtonian rheology affects the motion of biological and artificial micro swimmers, recent efforts have begun to seek answers to fundamental questions about active bodies in shear-thinning fluids. Previous analyses based on a squirmer model have revealed non-trivial variations of propulsion characteristics in a shear-thinning fluid via the reciprocal theorem. However, the reciprocal theorem approach does not provide knowledge about the flow surrounding the squirmer. In this work, we fill in this missing information by calculating the non-Newtonian correction to the flow analytically in the asymptotic limit of small Carreau number. In particular, we investigate the local effect due to viscosity reduction and the non-local effect due to induced changes in the flow; we then quantify their relative importance to locomotion in a shear-thinning fluid. Our results demonstrate cases where the non-local effect can be more significant than the local effect. These findings suggest that caution should be exercised when developing physical intuition from the local viscosity distribution alone around a swimmer in a shear-thinning fluid.
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