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Coherent structures and the saturation of a nonlinear dynamo
KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.ORCID iD: 0000-0002-7304-021X
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2013 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 729, 309-329 p.Article in journal (Refereed) Published
Abstract [en]

Eulerian and Lagrangian tools are used to detect coherent structures in the velocity and magnetic fields of a mean-field dynamo, produced by direct numerical simulations of the three-dimensional compressible magnetohydrodynamic equations with an isotropic helical forcing and moderate Reynolds number. Two distinct stages of the dynamo are studied: the kinematic stage, where a seed magnetic field undergoes exponential growth; and the saturated regime. It is shown that the Lagrangian analysis detects structures with greater detail, in addition to providing information on the chaotic mixing properties of the flow and the magnetic fields. The traditional way of detecting Lagrangian coherent structures using finite-time Lyapunov exponents is compared with a recently developed method called function M. The latter is shown to produce clearer pictures which readily permit the identification of hyperbolic regions in the magnetic field, where chaotic transport/dispersion of magnetic field lines is highly enhanced.

Place, publisher, year, edition, pages
2013. Vol. 729, 309-329 p.
Keyword [en]
chaotic advection, dynamo theory, MHD turbulence
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Other Physics Topics
URN: urn:nbn:se:kth:diva-133656DOI: 10.1017/jfm.2013.290ISI: 000322379400013ScopusID: 2-s2.0-84886260451OAI: diva2:663270

QC 20131111

Available from: 2013-11-11 Created: 2013-11-08 Last updated: 2013-11-11Bibliographically approved

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Brandenburg, Axel
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Nordic Institute for Theoretical Physics NORDITA
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