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Polish Academy of Sciences

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Recent publications
1.  Słowicka A.M., Xue N., Liu L., Nunes J.K., Sznajder P., Stone H.A., Ekiel-Jeżewska M.L., Highly elastic fibers in a shear flow can form double helices, NEW JOURNAL OF PHYSICS, ISSN: 1367-2630, DOI: 10.1088/1367-2630/ad56c0, Vol.26, pp.073011-1-18, 2024

Abstract:
The long-time behavior of highly elastic fibers in a shear flow is investigated experimentally and numerically. Characteristic attractors of the dynamics are found. It is shown that for a small ratio of bending to hydrodynamic forces, most fibers form a spinning elongated double helix, performing an effective Jeffery orbit very close to the vorticity direction. Recognition of these oriented shapes, and how they form in time, may prove useful in the future for understanding the time history of complex microstructures in fluid flows and considering processing steps for their synthesis.

Keywords:
Stokes equations, shear flow, elastic fibers

Affiliations:
Słowicka A.M. - IPPT PAN
Xue N. - other affiliation
Liu L. - IPPT PAN
Nunes J.K. - other affiliation
Sznajder P. - IPPT PAN
Stone H.A. - other affiliation
Ekiel-Jeżewska M.L. - IPPT PAN
2.  Słowicka A.M., Xue N., Sznajder P., Nunes J.K., Stone H.A., Ekiel-Jeżewska M.L., Buckling of elastic fibers in a shear flow, NEW JOURNAL OF PHYSICS, ISSN: 1367-2630, DOI: 10.1088/1367-2630/ac43eb, Vol.24, pp.013013-1-16, 2022

Abstract:
Three-dimensional dynamics of flexible fibers in shear flow are studied numerically, with a qualitative comparison to experiments. Initially, the fibers are straight, with different orientations with respect to the flow. By changing the rotation speed of a shear rheometer, we change the ratio A of bending to shear forces. We observe fibers in the flow-vorticity plane, which gives insight into the motion out of the shear plane. The numerical simulations of moderately flexible fibers show that they rotate along effective Jeffery orbits, and therefore the fiber orientation rapidly becomes very close to the flow-vorticity plane, on average close to the flow direction, and the fiber remains in an almost straight configuration for a long time. This ``ordering'' of fibers is temporary since they alternately bend and straighten out while tumbling. We observe numerically and experimentally that if the fibers are initially in the compressional region of the shear flow, they can undergo a compressional buckling, with a pronounced deformation of shape along their whole length during a short time, which is in contrast to the typical local bending that originates over a long time from the fiber ends. We identify differences between local and compressional bending and discuss their competition, which depends on the initial orientation of the fiber and the bending stiffness ratio A. There are two main finding. First, the compressional buckling is limited to a certain small range of the initial orientations, excluding those from the flow-vorticity plane. Second, since fibers straighten out in the flow-vorticity plane while tumbling, the compressional buckling is transient - it does not appear for times longer than 1/4 of the Jeffery period. For larger times, bending of fibers is always driven by their ends.

Keywords:
Stokes flow, flexible fibers, bending, buckling, orientational order

Affiliations:
Słowicka A.M. - IPPT PAN
Xue N. - other affiliation
Sznajder P. - IPPT PAN
Nunes J.K. - other affiliation
Stone H.A. - Princeton University (US)
Ekiel-Jeżewska M.L. - IPPT PAN

Conference abstracts
1.  Słowicka A.M., Xue N., Liu L., Nunes J., Sznajder P., Stone H.A., Ekiel-Jeżewska M.L., Dynamics of highly elastic fibers in a shear flow, EUROMECH Colloquium on Nonlinear Dynamics at Zero Reynolds Number, 2024-05-21/05-23, London (GB), pp.1, 2024
2.  Słowicka A.M., Xue N., Liu L., Nunes J., Sznajder P., Stone H.A., Ekiel-Jeżewska M.L., Very flexible fibers in a shear flow, ICTAM 2024, The 26th International Congress of Theoretical and Applied Mechanics, 2024-08-25/08-30, Daegu (KR), pp.1583-1584, 2024
3.  Słowicka A.M., Xue N., Sznajder P., Nunes J.K., Stone H.A., Ekiel-Jeżewska M.L., Short-time dynamics of elastic filaments in a shear flow, EUROMECH Colloquium 622, EUROMECH Colloquium 622, Suspension flows and rheology: inertia, shape and roughness matter, 2023-06-26/06-30, Nice (FR), pp.465184, 2023

Keywords:
Stokes equations, Euler-Bernoulli beam, elastica, elastic filament, shear flow, buckling

Affiliations:
Słowicka A.M. - IPPT PAN
Xue N. - other affiliation
Sznajder P. - IPPT PAN
Nunes J.K. - other affiliation
Stone H.A. - Princeton University (US)
Ekiel-Jeżewska M.L. - IPPT PAN
4.  Słowicka A.M., Xue N., Sznajder P., Nunes J.K., Stone H.A., Ekiel-Jeżewska M.L., Short-time dynamics of elastic fibers in a shear flow, FMC2022, XXV Fluid Mechanics Conference, 2022-09-07/09-09, Rzeszów (PL), pp.172-173, 2022

Keywords:
fluid dynamics, Stokes flows, particulate flows, hydrodynamic interactions, bending

Affiliations:
Słowicka A.M. - IPPT PAN
Xue N. - other affiliation
Sznajder P. - IPPT PAN
Nunes J.K. - other affiliation
Stone H.A. - Princeton University (US)
Ekiel-Jeżewska M.L. - IPPT PAN
5.  Ekiel-Jeżewska M.L., Słowicka A.M., Xue N., Sznajder P., Nunes J., Stone H.A., Buckling and temporal order of flexible fibers in shear flows, Bulletin of the American Physical Society, ISSN: 0003-0503, Vol.66, pp.M27.9, 2021

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