Reynolds number dependence of Lagrangian dispersion in direct numerical simulations of anisotropic magnetohydrodynamic turbulence

Pratt, J., Busse, A. and Müller, W.-C. (2022) Reynolds number dependence of Lagrangian dispersion in direct numerical simulations of anisotropic magnetohydrodynamic turbulence. Journal of Fluid Mechanics, 944, A36. (doi: 10.1017/jfm.2022.434)

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Abstract

Large-scale magnetic fields thread through the electrically conducting matter of the interplanetary and interstellar medium, stellar interiors and other astrophysical plasmas, producing anisotropic flows with regions of high-Reynolds-number turbulence. It is common to encounter turbulent flows structured by a magnetic field with a strength approximately equal to the root-mean-square magnetic fluctuations. In this work, direct numerical simulations of anisotropic magnetohydrodynamic (MHD) turbulence influenced by such a magnetic field are conducted for a series of cases that have identical resolution, and increasing grid sizes up to 20483. The result is a series of closely comparable simulations at Reynolds numbers ranging from 1400 up to 21 000. We investigate the influence of the Reynolds number from the Lagrangian viewpoint by tracking fluid particles and calculating single-particle and two-particle statistics. The influence of Alfvénic fluctuations and the fundamental anisotropy on the MHD turbulence in these statistics is discussed. Single-particle diffusion curves exhibit mildly superdiffusive behaviours that differ in the direction aligned with the magnetic field and the direction perpendicular to it. Competing alignment processes affect the dispersion of particle pairs, in particular at the beginning of the inertial subrange of time scales. Scalings for relative dispersion, which become clearer in the inertial subrange for a larger Reynolds number, can be observed that are steeper than indicated by the Richardson prediction.

Item Type:Articles
Additional Information:This material is based upon work supported by the National Science Foundation under grant no. PHY-1907876. A. B. gratefully acknowledges support via a Leverhulme Trust Research Fellowship. Simulations were performed on the Konrad and Gottfried computer systems of the Norddeutsche Verbund zur Förderung des Hoch- und Höchstleistungsrechnens (HLRN) by the project bep00051 ‘Lagrangian studies of incompressible turbulence in plasmas.’ Part of this work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Busse, Professor Angela
Authors: Pratt, J., Busse, A., and Müller, W.-C.
College/School:College of Science and Engineering > School of Engineering > Autonomous Systems and Connectivity
Journal Name:Journal of Fluid Mechanics
Publisher:Cambridge University Press
ISSN:0022-1120
ISSN (Online):1469-7645
Published Online:01 July 2022
Copyright Holders:Copyright © 2022 The Authors
First Published:First published in Journal of Fluid Mechanics 944:A36
Publisher Policy:Reproduced under a Creative Commons License

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