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| Titel |
A note on Taylor's hypothesis under large-scale flow variation |
| VerfasserIn |
M. Wilczek, H. Xu, Y. Narita |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1023-5809
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| Digitales Dokument |
URL |
| Erschienen |
In: Nonlinear Processes in Geophysics ; 21, no. 3 ; Nr. 21, no. 3 (2014-06-02), S.645-649 |
| Datensatznummer |
250120919
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| Publikation (Nr.) |
 copernicus.org/npg-21-645-2014.pdf |
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| Zusammenfassung |
| Experimental investigations of turbulent
velocity fields often invoke Taylor's hypothesis (also known as frozen
turbulence approximation) to evaluate the spatial structure based on
time-resolved single-point measurements. A crucial condition for the validity
of this approximation is that the turbulent fluctuations are small compared
to the mean velocity, in other words, that the turbulence intensity must be
low. While turbulence intensity is a well-controlled parameter in laboratory
flows, this is not the case in many geo- and astrophysical settings. Here we
explore the validity of Taylor's hypothesis based on a simple model for the
wavenumber-frequency spectrum that has recently been introduced as a
generalization of Kraichnan's random sweeping hypothesis. In this model, the
fluctuating velocity is decomposed into a large-scale random sweeping
velocity and small-scale fluctuations, which allows for a precise
quantification of the influence of large-scale flow variations. For
turbulence with a power-law energy spectrum, we find that the wavenumber
spectrum estimated by Taylor's hypothesis exhibits the same power-law as the
true spectrum, yet the spectral energy is overestimated due to the
large-scale flow variation. The magnitude of this effect, and specifically
its impact on the experimental determination of the Kolmogorov constant, are
estimated for typical turbulence intensities of laboratory and geophysical
flows. |
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