On the time scales and structure of Lagrangian intermittency in homogeneous isotropic turbulence
Artikel i vetenskaplig tidskrift, 2019

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.

topological fluid dynamics

turbulence simulation

Författare

Romain Watteaux

Stazione Zoologica Anton Dohrn

Gaetano Sardina

Chalmers, Mekanik och maritima vetenskaper, Strömningslära

Luca Brandt

Kungliga Tekniska Högskolan (KTH)

Daniele Iudicone

Stazione Zoologica Anton Dohrn

Journal of Fluid Mechanics

0022-1120 (ISSN) 1469-7645 (eISSN)

Vol. 867 438-481

Ämneskategorier

Övrig annan teknik

Strömningsmekanik och akustik

Fusion, plasma och rymdfysik

Fundament

Grundläggande vetenskaper

DOI

10.1017/jfm.2019.127

Mer information

Skapat

2019-04-29