Numerical and Experimental Investigation of Libration-Induced Planetary Fluid Dynamics

Details Numerical and Experimental Investigation of Libration-Induced Planetary Fluid Dynamics Numerical and Experimental Investigation of Libration-Induced Planetary Fluid Dynamics

Oct 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007dps....39.5110n&link_type=abstract

American Astronomical Society, DPS meeting #39, #51.10; Bulletin of the American Astronomical Society, Vol. 39, p.516

Physics

Fluid Dynamics

Scientific paper

Significant scientific resources are presently being devoted to the study of planetary bodies that undergo librational motions. Yet no comprehensive studies to date have investigated how libration affects interior planetary fluid dynamics. Our goal is to produce detailed experimental and numerical models of libration driven flows within planetary cores and briny subsurface oceans, which may prove relevant to our understanding of a number of planetary bodies including Mercury, Europa, Io, Callisto, Ganymede and the Earth's Moon.
In this first study, we investigate numerically and experimentally the hydrodynamic response of a fluid spherical shell to the libration of the outer boundary.
We focus on cases involving either a geometrically small inner core or no inner core; moderate Ekman number values (10-3-10-5) and synchronous libration frequencies. Different flow regimes are observed as the amplitude of libration α) is increased. At low α the ocillatory motion of the outer boundary drives inertial modes and waves in the fluid that are well predicted by full sphere analytical models (Stewartson and Roberts 1963; Greenspan 1968).
For larger amplitudes of librational, Taylor-Gortler rolls (e.g., Andereck et al 1985, Sha and Nakabayashi 2000) periodically develop during part of the cycle then dissipate. This roll instability is limited to a small portion of the fluid near the outer boundary. Eventually, for large enough libration amplitude, the entire fluid cavity becomes turbulent. After discussing the mechanisms underlying the different regimes, we will extrapolate our results to planetray core conditions.
The authors wish to the thank NASA's PG&G and PME Programs for reasearch funding (NNG0697G).

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