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On the time scales and structure of Lagrangian intermittency in homogeneous isotropic turbulence
Staz Zool Anton Dohrn, Lab Ecol & Evolut Plankton, I-80121 Naples, Italy..
Chalmers Univ Technol, Dept Mech & Maritime Sci, Fluid Dynam, SE-41296 Gothenburg, Sweden..
KTH, School of Engineering Sciences (SCI), Mechanics.ORCID iD: 0000-0002-4346-4732
Staz Zool Anton Dohrn, Lab Ecol & Evolut Plankton, I-80121 Naples, Italy..
2019 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 867, p. 438-481, article id 025301(R)Article in journal (Refereed) Published
Abstract [en]

We present a study of Lagrangian intermittency and its characteristic time scales. Using the concepts of flying and diving residence times above and below a given threshold in the magnitude of turbulence quantities, we infer the time spectra of the Lagrangian temporal fluctuations of dissipation, acceleration and enstrophy by means of a direct numerical simulation in homogeneous and isotropic turbulence. We then relate these time scales, first, to the presence of extreme events in turbulence and, second, to the local flow characteristics. Analyses confirm the existence in turbulent quantities of holes mirroring bursts, both of which are at the core of what constitutes Lagrangian intermittency. It is shown that holes are associated with quiescent laminar regions of the flow. Moreover, Lagrangian holes occur over few Kolmogorov time scales while Lagrangian bursts happen over longer periods scaling with the global decorrelation time scale, hence showing that loss of the history of the turbulence quantities along particle trajectories in turbulence is not continuous. Such a characteristic partially explains why current Lagrangian stochastic models fail at reproducing our results. More generally, the Lagrangian dataset of residence times shown here represents another manner for qualifying the accuracy of models. We also deliver a theoretical approximation of mean residence times, which highlights the importance of the correlation between turbulence quantities and their time derivatives in setting temporal statistics. Finally, whether in a hole or a burst, the straining structure along particle trajectories always evolves self-similarly (in a statistical sense) from shearless two-dimensional to shear bi-axial configurations. We speculate that this latter configuration represents the optimum manner to dissipate locally the available energy.

Place, publisher, year, edition, pages
Cambridge University Press, 2019. Vol. 867, p. 438-481, article id 025301(R)
Keywords [en]
topological fluid dynamics, turbulence simulation
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-249843DOI: 10.1017/jfm.2019.127ISI: 000462506900001Scopus ID: 2-s2.0-85063598590OAI: oai:DiVA.org:kth-249843DiVA, id: diva2:1307302
Note

QC 20190426

Available from: 2019-04-26 Created: 2019-04-26 Last updated: 2019-04-26Bibliographically approved

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