# Approche expérimentale de la turbulence par mesuresde viscosité apparente dans les fluides en rotation.Application au couplage visco-magnétique de l'interface noyau-manteau.

Abstract : We present an experimental method to estimate the eddy viscosity in rotating bounding fluids. By measures of the azimuthal component of the velocity during spin-up/spin-down experiments, we retrieve the viscosity (using the linear theory of Greenspan). Differences between laminar and turbulent regimes give an estimate of the momentum transport between fluid and boundaries operated by eddies.
Works have been done on four experiments in order to evaluate the impact of the geometry and the contribution of turbulent mechanisms. Both interact in the change of eddy viscosity. In experiments of thermal convection in spherical shell, the increase of eddy viscosity is explained by a scaling law in $\frac{Ra}{Ra_c}E^{1/3}$. For the remainder experiments, the change in viscosity is not uniform in the volume and no global quantities can modelize this effect. This change may be explained by the turbulent mechanism (experiment of differential rotation) or by instabilities that develop during convective spin-up (experiment of convection in cylindrical geometry).
Theoretical work has also been done. Differential rotation between core and mantle induce torques and we derive the visco-magnetic torque at the CMB for spin over motions. We estimate the influence of eddy viscosity, electrical conductivity of the mantle, geometry and intensity of the magnetic field on the visco-magnetic torque.
The value of the coupling constant given by nutation models shows that apparent viscosity $10^{-2}$ m^{2}.s^{-1}$($10^{4}\$ bigger that the liquid iron molecular viscosity) is needed to explain nutation's data.
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Submitted on : Friday, April 7, 2006 - 4:28:30 PM
Last modification on : Tuesday, October 19, 2021 - 6:58:05 PM
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### Identifiers

• HAL Id : tel-00012097, version 1

### Citation

Bérangère Deleplace. Approche expérimentale de la turbulence par mesures
de viscosité apparente dans les fluides en rotation.
Application au couplage visco-magnétique de l'interface noyau-manteau.. Géophysique [physics.geo-ph]. Université Joseph-Fourier - Grenoble I, 2005. Français. ⟨tel-00012097⟩

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