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| Titel |
Geophysical flow simulation experiment ‘GeoFlow II' - steps towards a mantle convection experiment in spherical shells |
| VerfasserIn |
Birgit Futterer, Norman Dahley, Nicoleta Scurtu, Christoph Egbers, Ana-Catalina Plesa, Doris Breuer |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250032946
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| Zusammenfassung |
| Thermal convection is a central objective in geo- and astrophysical research. To model
convection by an experiment in the GeoFlow project we consider the fluid motion in a gap
between two concentric spheres, with inner spherical shell heated and outer spherical shell
cooled. Central symmetry buoyancy field is set-up by means of a high voltage potential and
use of a dielectric liquid as working fluid in the spherical cavity. This technique, i.e. realize a
self-gravitating force field experimentally, requires microgravity conditions in order to
reduce unidirectional influence of gravity, that would dominate fluid flow in the
laboratory. For GeoFlow this specific conditions are available in the European module
COLUMBUS of the International Space Station ISS. During mission GeoFlow I, which was
running on orbit from July 2008 until January 2009, shells were filled with a fluid
having approximately constant viscosity, i.e. silicone oil. Motivated by convective
motion of the Earth’s outer core, patterns of convection and their spatial-temporal
behaviour have been prospected. For the planned second mission GeoFlow II (on orbit
2010) we propose to use nonanol as working fluid, having a temperature dependent
viscosity. Herewith experimental modelling of mantle convection is the central
goal.
Governing equations in Boussinesq form for the incompressible Newtonian fluid of
nonanol are dominated by inertia. In contrast to traditional computer simulation work for
mantle dynamics the Prandtl number for our planned experiment is reasonable high (Pr -¤
200), and not infinite. Therefore in a first step this Prandtl number influence have been
benchmarked with the spherical code GAIA assuming an isoviscous fluid and set-up with an
infinite Prandtl number. As a conclusion from these numerical tests, the Prandtl number can
be dropped. Next steps are to simulate variations of thermal forcing (variation of Rayleigh
number) with the specific viscosity contrast of nonanol. Here experimental realization offers
the possibility to vary the viscosity contrast by variation of the working regime, too. |
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