Fiber Tracking Velocimetry for Two-Point Statistics of Turbulence

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...

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Autores principales:	Stefano Brizzolara, Marco Edoardo Rosti, Stefano Olivieri, Luca Brandt, Markus Holzner, Andrea Mazzino
Formato:	article
Lenguaje:	EN
Publicado:	American Physical Society 2021
Materias:	Physics QC1-999
Acceso en línea:	https://doaj.org/article/46c84baf7e0d411a981714e2556c6760
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spelling	oai:doaj.org-article:46c84baf7e0d411a981714e2556c67602021-11-18T18:45:37ZFiber Tracking Velocimetry for Two-Point Statistics of Turbulence10.1103/PhysRevX.11.0310602160-3308https://doaj.org/article/46c84baf7e0d411a981714e2556c67602021-09-01T00:00:00Zhttp://doi.org/10.1103/PhysRevX.11.031060http://doi.org/10.1103/PhysRevX.11.031060https://doaj.org/toc/2160-3308We 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.Stefano BrizzolaraMarco Edoardo RostiStefano OlivieriLuca BrandtMarkus HolznerAndrea MazzinoAmerican Physical SocietyarticlePhysicsQC1-999ENPhysical Review X, Vol 11, Iss 3, p 031060 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	Physics QC1-999
spellingShingle	Physics QC1-999 Stefano Brizzolara Marco Edoardo Rosti Stefano Olivieri Luca Brandt Markus Holzner Andrea Mazzino Fiber Tracking Velocimetry for Two-Point Statistics of Turbulence
description	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.
format	article
author	Stefano Brizzolara Marco Edoardo Rosti Stefano Olivieri Luca Brandt Markus Holzner Andrea Mazzino
author_facet	Stefano Brizzolara Marco Edoardo Rosti Stefano Olivieri Luca Brandt Markus Holzner Andrea Mazzino
author_sort	Stefano Brizzolara
title	Fiber Tracking Velocimetry for Two-Point Statistics of Turbulence
title_short	Fiber Tracking Velocimetry for Two-Point Statistics of Turbulence
title_full	Fiber Tracking Velocimetry for Two-Point Statistics of Turbulence
title_fullStr	Fiber Tracking Velocimetry for Two-Point Statistics of Turbulence
title_full_unstemmed	Fiber Tracking Velocimetry for Two-Point Statistics of Turbulence
title_sort	fiber tracking velocimetry for two-point statistics of turbulence
publisher	American Physical Society
publishDate	2021
url	https://doaj.org/article/46c84baf7e0d411a981714e2556c6760
work_keys_str_mv	AT stefanobrizzolara fibertrackingvelocimetryfortwopointstatisticsofturbulence AT marcoedoardorosti fibertrackingvelocimetryfortwopointstatisticsofturbulence AT stefanoolivieri fibertrackingvelocimetryfortwopointstatisticsofturbulence AT lucabrandt fibertrackingvelocimetryfortwopointstatisticsofturbulence AT markusholzner fibertrackingvelocimetryfortwopointstatisticsofturbulence AT andreamazzino fibertrackingvelocimetryfortwopointstatisticsofturbulence
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Fiber Tracking Velocimetry for Two-Point Statistics of Turbulence

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