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| Titel |
Measuring the cascade rate in anisotropic turbulence through 3rd order structure functions. |
| VerfasserIn |
Andrea Verdini, Simone Landi, Petr Hellinger |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250088121
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| Publikation (Nr.) |
 EGU/EGU2014-2197.pdf |
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| Zusammenfassung |
| We employ the Von-Karman-Howart-Yaglom-Politano-Poquet (KHYPP)law,
to compute the cascade rate by means of 3rd order structure functions
in homogeneous, forced, DNS at high resolution.
We consider first the isotropic case (no guide field) and verify that the
cascade rate is consistent with the dissipation rate. Then we consider an
anisotropic case (with guide field) for which the isotropic KHYPP law does not
apply. We compute the parallel and perpendicular cascade rates and find that
the latter basically accounts for the total dissipation rate, as expected for
anisotropic turbulence. Also, the cascade rate derived from the isotropic law
is found to be a good approximation for the total cascade rate.
Recent works have shown that the hypothesis of stationary turbulence must be
probably relaxed in the solar wind. We present preliminary results on the
measure of the cascade rate in the expanding solar wind, obtained with DNS of
MHD turbulence in the expanding box model. Such model incorporates the basic
physic of expansion thus inducing anisotropies driven by both the magnetic
field and expansion, along with an energy decrease due to the conservation of
linear invariants (angular momentum and magnetic flux). The correction due to
non-stationary conditions is found to be important and to become negligible
only at small scales, thus suggesting that solar wind measurements over-
estimate the actual cascade rate. |
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