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| Titel |
Sheet-like and plume-like thermal flow in a spherical convection experiment with high viscosity contrast. |
| VerfasserIn |
Birgit Futterer, Florian Zaussinger, Ana-Catalina Plesa, Andreas Krebs, Christoph Egbers, Doris Breuer |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250076118
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| Zusammenfassung |
| We introduce our spherical experiments on electro-hydrodynamical driven Rayleigh-Bénard
convection that have been performed either with temperature-independent properties of the
fluid, called ‘GeoFlow I’, or with temperature-dependent properties, called ‘GeoFlow II’. To
set up a self-gravitating force field with radial directed buoyancy, we use a high voltage
potential between the inner and outer boundaries and a dielectric insulating liquid and
perform the experiment in the microgravity conditions of the ISS [1, 2]. We further run
numerical simulations in a 3D spherical geometry to reproduce the results obtained in the
GeoFlow experiments.
In the experiment the used optical method for flow visualization as delivered by the
Optical Diagnostics Module ODM of the Fluid Science Laboratory, is the so called
Wollaston-Prism shearing interferometry WSI, which produces fringe pattern images. For the
numerical simulations we compute from the temperature field a fringe pattern of convection
to compare it then to the experiment data. In this work, we present the flow imaging
techniques and their numerical analogues, which were used to compare experimental results
with numerical solutions.
An important finding is the difference in the flow pattern between our two experiments.
We see a sheet-like thermal flow, if the physical properties of the fluid are not varying with
temperature - a result from ‘GeoFlow I’. In this case the convection patterns have been
successfully reproduced by 3D numerical simulations using both the RESPECT [3] and
GAIA [4] codes. If we use a liquid with varying (electro-hydrodynamic) volume
expansion and temperature-dependent viscosity (GeoFlow II), for which the viscosity
contrast measured in the experiment is 2, the structures change significantly and are
plume-like. This result is not expected, since the viscosity contrast seems to be too
small for this type of solution according to numerical simulations. However, using a
viscosity contrast of two orders of magnitude or higher, we can reproduce the patterns
obtained in the GeoFlow II experiment, implying that non-linear effects shift the
effective viscosity ratio. Hence, the GeoFlow II experiment gives the possibility to
study flows under high viscosity contrasts and is a promising candidate as reference
experiment.
REFERENCES [1] B. Futterer, C. Egbers, N. Dahley, S. Koch, L. Jehring (2010). Acta
Astronautica 66. [2] B. Futterer, N. Dahley, S. Koch, N. Scurtu, C. Egbers (2012). Acta
Astronautica 71. [3] R. Hollerbach, R., (2000). International Journal for Numerical Methods
in Fluids 32. [4] C. Huettig, K. Stemmer, (2008). PEPI. |
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