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| Titel |
Rotational acoustics in spherical Couette experiments |
| VerfasserIn |
S. A. Triana, H.-C. Nataf, D. Zimmerman, M. Adams, D. P. Lathrop, D. Schmitt, P. Cardin, A. Richard, P. La Rizza, J.-P. Masson, S. Cabanes, P. Roux |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250064897
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| Zusammenfassung |
| Helioseismologists retrieve differential rotation profiles within the Sun by inverting the
splitting of acoustic modes. We have explored the idea of using a similar technique in fluid
dynamics Lab experiments. Spherical Couette experiments are particularly appealing because
acoustic modes in a fluid spherical shell are readily computed. Two experimental set-ups
have been used for the tests: DTS in Grenoble, and a 30-cm diameter experiment in
Maryland. In DTS, liquid sodium is sheared between two concentric spheres in a dipolar
magnetic field. The 30-cm experiment has the same geometry but is filled with
air.
The acoustic waves are generated by tapping the container, or with a loudspeaker, or from
internal noise. They are recorded by pressure-sensors mounted flush on the outer sphere. In
all cases, sharp spectral peaks are observed, with frequencies that match the expected values.
In DTS, some 50 acoustic modes are observed in the 3kHz-50kHz-frequency range.
Replacing sodium with argon permits to identify and remove modes that have a different
origin.
We have investigated the effect of differential rotation on the acoustic modes, by
spinning the inner sphere up to 30Hz. Even for this large forcing, the highest frequency
modes (>40kHz) show up above the turbulent spectrum. Some of these modes are
very clearly split when differential rotation is present. We will present these novel
observations, and discuss the potential of the rotational acoustic method in fluid mechanics
experiments.
This new technique will soon be implemented on the Maryland BigSister dynamo
experiment, filled with 15000 litres of liquid sodium. |
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