FSL Experiment GeoFlow for Geophysical Motivated Convective Phenomena

Paper number

IAC-08.A2.3.4

Author

Prof. Christoph Egbers , BTU Cottbus, Germany

Coauthor

Mrs. Birgit Futterer, Brandenburg University of Technology Cottbus, Germany

Year

2008

Abstract

Objective of GeoFlow experiment is to study thermally-driven rotating fluids, in order to investigate the stability, pattern formation, and transition to turbulence of viscous incompressible fluids contained between concentric, co-axially rotating spheres. These physical mechanisms are important for a large number of astrophysical and geophysical problems showing flows in spherical geometry driven by rotation and convection: for example, to explain the mantle convection of the Earth, or the flow in a planet's interior (like the Earth). Focusing on main acting forces for example in the inner Earth, that is temperature gradients and rotation, and neglecting magnetic effects in order to stress thermal and rotating aspects of the theoretical formulation and experimental set-up, that corresponds to research on stability and pattern formation of thermal convection in a rotating spherical gap.
If phenomena are studied experimentally in an Earth lab, gravity acts axial to a spherical model, and not central, like in the Earth's core. Such a central force field can be setup using the dielectrophoretic effect by applying a high voltage alternating field on the inner sphere which is than acting as a spherical capacitor. Resulting artificial central acceleration amounts to approximately 10-3 m/s2, showing that acceleration due to gravity with g~10m/s2 will always be dominant in an Earth laboratory. Necessary microgravity conditions for research, due to thermal experiments especially required long-term ones, are available at the International Space Station (ISS). Optical measurement methods as Wollaston shearing interferometry is used to determine the temperature fields and flow patterns.
Here we present numerical preliminary studies which focus on dynamics of non-rotational and rotational regimes. For non-rotational case an approach combining numerical simulations with a spectral time-stepping code and path-following techniques allows the computation of both stable and unstable solution branches of stationary states. The transition from the stationary to the time-dependent regime is described. Direct numerical simulation of rotational regimes show bifurcation from basic via periodic and quasi-periodic state into chaos. In the low rotation regime drift of time-dependent solutions is prograde while in the higher rotation regime drift is retrograde with rotation of the sphere.
We expect to compare those numerical predictions of different thermal flow states with first
experimental data from ISS experiment.

Abstract document

IAC-08.A2.3.4.pdf

Manuscript document

IAC-08.A2.3.4.pdf (🔒 authorized access only).

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