14–18 Feb 2011
Wenner Gren Center
Europe/Stockholm timezone

Passive scalar and magnetic field transport in potential flows

16 Feb 2011, 14:00
30m
Wenner-Gren Center, floor 7, Hörsalen (Wenner Gren Center)

Wenner-Gren Center, floor 7, Hörsalen

Wenner Gren Center

Sveavägen 164 SE-113 46 Stockholm Sweden

Speaker

Prof. Karl-Heinz Raedler (Astrophysical Institute Potsdam)

Description

It is demonstrated that the total mean-field diffusivity for passive scalar transport in a compressible fluid showing isotropic turbulence may well be smaller than the molecular diffusivity. This is in full analogy to the old finding regarding the magnetic mean-field diffusivity in an electrically conducting turbulently moving compressible fluid (e.g. Krause and Rädler 1980). For both the passive scalar and the magnetic case several analytical results on mean-field diffusivities found within the second-order correlation approximation are presented as well as numerical results obtained by the test-field method, which apply independent of this approximation. Mean-field diffusivities smaller than the molecular diffusivities may occur in compressible turbulence for not too large Peclet or magnetic Reynolds numbers and, in addition, slow variations of the flow patterns. Analogous results has also been found in simple model of anisotropic potential-flow turbulence. The decay of mean fields under the influence of compressible turbulence is strongly influenced by the so-called memory effect (Hubbard and Brandenburg 2009), that is, the relevant diffusivity coefficients depend on the decay rates.

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