Zonal Acoustic Velocimetry in 30-cm, 60-cm, and 3-m Laboratory Models of the Outer Core
Abstract
A knowledge of zonal flows and shear is key in understanding magnetic field dynamics in the Earth and laboratory experiments with Earth-like geometries. Traditional techniques for measuring fluid flow using visualization and particle tracking are not well-suited to liquid metal flows. This has led us to develop a flow measurement technique based on acoustic mode velocimetry adapted from helioseismology. As a first step prior to measurements in the liquid sodium experiments, we implement this technique in our 60-cm diameter spherical Couette experiment in air. To account for a more realistic experimental geometry, including deviations from spherical symmetry, we compute predicted frequencies of acoustic normal modes using the finite element method. The higher accuracy of the predicted frequencies allows the identification of over a dozen acoustic modes, and mode identification is further aided by the use of multiple microphones and by analyzing spectra together with those obtained at a variety of nearby Rossby numbers. Differences between the predicted and observed mode frequencies are caused by differences in flow patterns present in the experiment. We compare acoustic mode frequency splittings with theoretical predictions for stationary fluid and solid body flow condition with excellent agreement. We also use this technique to estimate the zonal shear in those experiments across a range of Rossby numbers. Finally, we report on initial attempts to use this in liquid sodium in the 3-meter diameter experiment and parallel experiments performed in water in the 30-cm diameter experiment.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMGP23B1336R
- Keywords:
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- 1510 Dynamo: theories and simulations;
- GEOMAGNETISM AND PALEOMAGNETISMDE: 5430 Interiors;
- PLANETARY SCIENCES: SOLID SURFACE PLANETSDE: 8120 Dynamics of lithosphere and mantle: general;
- TECTONOPHYSICSDE: 8121 Dynamics: convection currents;
- and mantle plumes;
- TECTONOPHYSICS