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Études expérimentales en magnétohydrodynamique : effet dynamo, turbulence et induction.

Abstract : This PhD work concentrates on three issues of magnetohydrodynamics : the dynamo effect, magnetic in- duction from flow motions and flow modifications from large applied magnetic fields. Experiments are run using von Karman flows, either in Lyon with gallium as the working fluid or Cadarache using liquid sodium, in the framework of the VKS dynamo collaborations. One issue concerns the effect of boundary conditions on induction, as evidenced by the VKS experiment for which dynamo generation has only been observed when at least on rotating driving impeller is made of soft iron. In the gallium flow, measurements made with driving impellers made with materials of variable electrical conductivity and magnetic permeability show that strong induction effects are generated in the vicinity of the iron impeller(s). Another issue concerns the link between the chaotic behavior of the magnetic field and the dynamic of the hydrodynamics flow. We build a semi-homogeneous dynamo with a turbulent ω-effect and an artificial α-effect. In this experiment, dynamo reversals are observed, with the characteristics of on-off intermittency, governed by the large scale fluctuation of the flow. This dynamics can be modeled by a system with additive and multiplicative noise. As the dynamo saturates to its equilibrium value, Lorentz forces modify the the flow. In order to study this mechanism, we have build two kinds of velocity probes which can operate in liquid metals. Using global power measurements, we also show how a large magnetic field modify the structure and the dynamics of the von Karman swirling flows.
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https://tel.archives-ouvertes.fr/tel-00533555
Contributor : Gautier Verhille <>
Submitted on : Sunday, November 7, 2010 - 4:55:21 PM
Last modification on : Saturday, November 21, 2020 - 3:09:24 AM
Long-term archiving on: : Friday, October 26, 2012 - 3:10:14 PM

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  • HAL Id : tel-00533555, version 1

Citation

Gautier Verhille. Études expérimentales en magnétohydrodynamique : effet dynamo, turbulence et induction.. Physique [physics]. Ecole normale supérieure de lyon - ENS LYON, 2010. Français. ⟨tel-00533555⟩

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