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alpha effect in a turbulent liquid-metal plane Couette flow
KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.ORCID iD: 0000-0002-7304-021X
2014 (English)In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, Vol. 89, no 3, 033009- p.Article in journal (Refereed) Published
Abstract [en]

We calculate the mean electromotive force in plane Couette flows of a nonrotating conducting fluid under the influence of a large-scale magnetic field for driven turbulence. A vertical stratification of the turbulence intensity results in an alpha effect owing to the presence of horizontal shear. Here we discuss the possibility of an experimental determination of the components of the alpha tensor using both quasilinear theory and nonlinear numerical simulations. For magnetic Prandtl numbers of the order of unity, we find that in the high-conductivity limit the alpha effect in the direction of the flow clearly exceeds the component in spanwise direction. In this limit, alpha runs linearly with the magnetic Reynolds number Rm, while in the low-conductivity limit it runs with the product Rm . Re, where Re is the kinetic Reynolds number, so that for a given Rm the alpha effect grows with decreasing magnetic Prandtl number. For the small magnetic Prandtl numbers of liquid metals, a common value for the horizontal elements of the alpha tensor appears, which makes it unimportant whether the alpha effect is measured in the spanwise or the streamwise directions. The resulting effect should lead to an observable voltage of about 0.5 mV in both directions for magnetic fields of 1 kG and velocity fluctuations of about 1 m/s in a channel of 50-cm height (independent of its width).

Place, publisher, year, edition, pages
2014. Vol. 89, no 3, 033009- p.
Keyword [en]
Mean-Field Dynamos, Simulations
National Category
Physical Sciences
URN: urn:nbn:se:kth:diva-143974DOI: 10.1103/PhysRevE.89.033009ISI: 000332672700006ScopusID: 2-s2.0-84898946549OAI: diva2:710465
EU, European Research Council, 227952Swedish Research Council, 621-2011-5076 2012-5797

QC 20140407

Available from: 2014-04-07 Created: 2014-04-04 Last updated: 2014-04-07Bibliographically approved

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Brandenburg, Axel
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