Journal Article

FZJ-2021-04878

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Theoretical framework for two-microswimmer hydrodynamic interactions

Ziegler, S.FZJ* ; Scheel, T.FZJ* ; Hubert, M.FZJ* ; Harting, J.FZJ* ; Smith, A.-S. (Corresponding author)FZJ*

2021
IOP [London]

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Please use a persistent id in citations: http://hdl.handle.net/2128/29294  doi:10.1088/1367-2630/ac1141

Abstract: Hydrodynamic interactions are crucial for determining the cooperative behavior ofmicroswimmers at low Reynolds numbers. Here we provide a comprehensive analysis of thescaling laws and the strength of the interactions in the case of a pair of three-sphere swimmers.Both stroke-based and force-based elastic microswimmers are analyzed using an analyticperturbative approach, focusing on passive and active interactions. The former are governed by thecycle-averaged flow field of a single swimmer, which is dipolar at long range. However, atintermediate distances, with a cross-over at the order of 102 swimmer lengths, the quadrupolarfield dominates which, notably, yields an increase of the swimming velocity compared toindividual swimmers, even when the swimmers are one behind another. Furthermore, we find thatactive rotations resulting from the interplay of the time-resolved swimming stroke and the ambientflow fields and, even more prominently, active translations are model-dependent. A mappingbetween the stroke-based and force-based swimmers is only possible for the low driving frequencyregime where the characteristic time scale is smaller than the viscous one. Finally, we find that thelong-term behavior of the swimmers, while sensitive to the initial relative positioning, does notdepend on the pusher or puller nature of the swimmer. These results clearly indicate that thebehavior of swarms will depend on the swimmer model, which was hitherto not well appreciated.

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Contributing Institute(s):

1. Helmholtz-Institut Erlangen-Nürnberg Erneuerbare Energien (IEK-11)

Research Program(s):

1. 1215 - Simulations, Theory, Optics, and Analytics (STOA) (POF4-121) (POF4-121)
2. DFG project 366087427 - Magnetokapillare Mikroroboter zum Einfangen und zum Transport von Objekten an Flüssiggrenzflächen (366087427)

Appears in the scientific report 2021

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