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Induced drift by a self-propelled swimmer at intermediate Reynolds numbers

Nawroth, Janna C. and Dabiri, John O. (2014) Induced drift by a self-propelled swimmer at intermediate Reynolds numbers. Physics of Fluids, 26 (9). Art. No. 091108. ISSN 1070-6631. http://resolver.caltech.edu/CaltechAUTHORS:20141106-084157113

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Abstract

Swimming organisms have been proposed to contribute to the mixing of stratified water in the ocean, thereby facilitating the vertical transport of nutrients and dissolved gases. In general, mixing results from increasing the interface available for molecular diffusion between neighboring fluid volumes. At high Reynolds numbers (Re), swimmers generate such interfaces through their turbulent wake structures. At lower Re, however, turbulent mixing becomes ineffective as viscous effects dissipate small-scale fluid motions as heat, and diffusion is not significantly enhanced. In this regime, it appears that the dominant mechanism for mixing by a swimmer is induced drift, i.e., the propagation and stretching of a fluid volume by a moving body's pressure field, which increases the diffusion-enabling interface between the drift volume and surrounding fluid. The ratio of drift volume to body volume is called the “added-mass” coefficient and depends on the shape of the body. Importantly, previous computational analysis suggested that the total drift volume increases at low and intermediate Re, 3 implying that in contrast to turbulent mixing, mixing through induced drift becomes more efficient in viscous conditions. As pointed out by others, the limitation of previous numerical simulations, however, is that the simulated objects were towed through viscous fluid, which is dynamically distinct from a self-propelled swimmer. Using qualitative flow visualization, we here demonstrate the presence of induced drift in self-propelled swimmers operating at intermediate Re (1–100). In these experiments, the spatiotemporal pattern of a fluid volume initially surrounding a juvenile Moon jellyfish ( Aurelia aurita) is visualized using Fluorescein dye (see Fig. 1 ). For details on the experimental methods see supplemental material in Ref. 13 .


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http://dx.doi.org/10.1063/1.4893537 DOIArticle
http://scitation.aip.org/content/aip/journal/pof2/26/9/10.1063/1.4893537PublisherArticle
Additional Information:© 2014 AIP Publishing LLC. Received 27 July 2014; published online 19 September 2014. We gratefully acknowledge financial support from the U.S.-Israel Binational Science Foundation.
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U.S.-Israel Binational Science FoundationUNSPECIFIED
Record Number:CaltechAUTHORS:20141106-084157113
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20141106-084157113
Official Citation:Induced drift by a self-propelled swimmer at intermediate Reynolds numbers Nawroth, Janna C. and Dabiri, John O., Physics of Fluids (1994-present), 26, 091108 (2014), DOI:http://dx.doi.org/10.1063/1.4893537
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:51347
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:06 Nov 2014 16:57
Last Modified:06 Nov 2014 16:57

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