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Fiber Tracking Velocimetry for Two-Point Statistics of Turbulence
Institute of Environmental Engineering, ETH Zurich, CH-8039 Zürich, Switzerland; Swiss Federal Institute of Forest, Snow and Landscape Research WSL, Birmensdorf, 8903, Switzerland..ORCID iD: 0000-0002-4616-5033
Complex Fluids and Flows Unit, Okinawa Institute of Science and Technology Graduate University, 1919-1 Tancha, Onna-son, Okinawa, 904-0495, Japan..ORCID iD: 0000-0002-9004-2292
Complex Fluids and Flows Unit, Okinawa Institute of Science and Technology Graduate University, 1919-1 Tancha, Onna-son, Okinawa, 904-0495, Japan; DICCA, University of Genova and INFN, Genova Section, Via Montallegro 1, Genova, 16145, Italy..ORCID iD: 0000-0002-7795-6620
KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.ORCID iD: 0000-0002-4346-4732
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2021 (English)In: Physical Review X, E-ISSN 2160-3308, Vol. 11, no 3, article id 031060Article in journal (Refereed) Published
Abstract [en]

We propose and validate a novel experimental technique to measure two-point statistics of turbulent flows. It consists of spreading rigid fibers in the flow and tracking their position and orientation in time and is therefore named “fiber tracking velocimetry.” By choosing different fiber lengths, i.e., within the inertial or dissipative range of scales, the statistics of turbulence fluctuations at the selected length scale can be probed accurately by simply measuring the fiber velocity at its two ends and projecting it along the transverse-to-fiber direction. By means of fully resolved direct numerical simulations and experiments, we show that these fiber-based transverse velocity increments are statistically equivalent to the (unperturbed) flow transverse velocity increments. Moreover, we show that the turbulent energy-dissipation rate can be accurately measured exploiting sufficiently short fibers. The technique is tested against standard particle tracking velocimetry (PTV) of flow tracers with excellent agreement. Our technique overcomes the well-known problem of PTV to probe two-point statistics reliably because of the fast relative diffusion in turbulence that prevents the mutual distance between particles to remain constant at the length scale of interest. This problem, making it difficult to obtain converged statistics for a fixed separation distance, is even more dramatic for natural flows in open domains. A prominent example is oceanic currents, where drifters (i.e., the tracer-particle counterpart used in field measurements) disperse quickly, but at the same time their number has to be limited to save costs. Inspired by our laboratory experiments, we propose pairs of connected drifters as a viable option to solve the issue.

Place, publisher, year, edition, pages
American Physical Society (APS) , 2021. Vol. 11, no 3, article id 031060
Keywords [en]
Energy dissipation, Fibers, Ocean currents, Statistics, Turbulence, Velocimeters, Experimental techniques, Fiber length, Fiber tracking, Length scale, Particle-tracking velocimetry, Position and orientations, Rigid fibers, Transverse velocity, Two point statistics, Velocity increments, Velocity measurement
National Category
Fluid Mechanics
Identifiers
URN: urn:nbn:se:kth:diva-312076DOI: 10.1103/PhysRevX.11.031060ISI: 000704691600001Scopus ID: 2-s2.0-85116314475OAI: oai:DiVA.org:kth-312076DiVA, id: diva2:1657517
Note

QC 20220511

Available from: 2022-05-11 Created: 2022-05-11 Last updated: 2025-02-09Bibliographically approved

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Rosti, Marco E.Brandt, Luca

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Brizzolara, StefanoRosti, Marco E.Olivieri, StefanoBrandt, LucaHolzner, MarkusMazzino, Andrea
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Linné Flow Center, FLOWSeRC - Swedish e-Science Research CentreFluid Mechanics and Engineering Acoustics
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Physical Review X
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