Journal
JOURNAL OF FLUID MECHANICS
Volume 735, Issue -, Pages 647-683Publisher
CAMBRIDGE UNIV PRESS
DOI: 10.1017/jfm.2013.507
Keywords
Benard convection; geophysical and geological flows; nonlinear dynamical systems
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Funding
- ESA [AO-99-049]
- German Aerospace Center DLR [50 WM 0122, 50 WM 0822]
- 'GeoFlow' Topical Team [18950/05/NL/VJ]
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We introduce, in spherical geometry, experiments on electro-hydrodynamic driven Rayleigh-Benard convection that have been performed for both temperature-independent ('GeoFlow I') and temperature-dependent fluid viscosity properties ('GeoFlow II') with a measured viscosity contrast up to 1.5. To set up a self-gravitating force field, we use a high-voltage potential between the inner and outer boundaries and a dielectric insulating liquid; the experiments were performed under microgravity conditions on the International Space Station. We further run numerical simulations in three-dimensional spherical geometry to reproduce the results obtained in the 'GeoFlow' experiments. We use Wollaston prism shearing interferometry for flow visualization - an optical method producing fringe pattern images. The flow patterns differ between our two experiments. In GeoFlow I', we see a sheet-like thermal flow. In this case convection patterns have been successfully reproduced by three-dimensional numerical simulations using two different and independently developed codes. In contrast, in 'GeoFlow II', we obtain plume-like structures. Interestingly, numerical simulations do not yield this type of solution for the low viscosity contrast realized in the experiment. However, using a viscosity contrast of two orders of magnitude or higher, we can reproduce the patterns obtained in the ` GeoFlow II' experiment, from which we conclude that nonlinear effects shift the effective viscosity ratio.
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