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| Titel |
Spectral element simulation of precession driven flows in the outer cores of spheroidal planets |
| VerfasserIn |
Jan Vormann, Ulrich Hansen |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250105294
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| Publikation (Nr.) |
 EGU/EGU2015-4791.pdf |
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| Zusammenfassung |
| A common feature of the planets in the solar system is the precession of the rotation axes,
driven by the gravitational influence of another body (e.g. the Earth’s moon). In a precessing
body, the rotation axis itself is rotating around another axis, describing a cone during one
precession period. Similar to the coriolis and centrifugal force appearing from the
transformation to a rotating system, the addition of precession adds another term to
the Navier-Stokes equation, the so called Poincaré force. The main geophysical
motivation in studying precession driven flows comes from their ability to act as
magnetohydrodynamic dynamos in planets and moons. Precession may either act as the
only driving force or operate together with other forces such as thermochemical
convection.
One of the challenges in direct numerical simulations of such flows lies in the spheroidal
shape of the fluid volume, which should not be neglected since it contributes an additional
forcing trough pressure torques. Codes developed for the simulation of flows in spheres
mostly use efficient global spectral algorithms that converge fast, but lack geometric
flexibility, while local methods are usable in more complex shapes, but often lack high
accuracy.
We therefore adapted the spectral element code Nek5000, developed at Argonne National
Laboratory, to the problem. The spectral element method is capable of solving for the flow in
arbitrary geometries while still offering spectral convergence. We present first results for the
simulation of a purely hydrodynamic, precession-driven flow in a spheroid with
no-slip boundaries and an inner core. The driving by the Poincaré force is in a
range where theoretical work predicts multiple solutions for a laminar flow. Our
simulations indicate a transition to turbulent flows for Ekman numbers of 10-6 and lower. |
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