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Impact of impellers on the axisymmetric magnetic mode in the VKS2 dynamo experiment

par Laguerre, Raphaël ;Nore, Caroline;Ribeiro, Adolfo;Guermond, Jean Luc;Léorat, Jacques;Plunian, Franck
Référence Physical review letters, 101, 10, 104501
Publication Publié, 2008-09

Article révisé par les pairs

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Résumé :

In the von Kármán Sodium 2 (VKS2) successful dynamo experiment of September2006, the observed magnetic field showed a strong axisymmetric component, implying that nonaxisymmetric components of the flow field were acting. By modeling the induction effect of the spiraling flow between the blades of the impellers in a kinematic dynamo code, we find that the axisymmetric magnetic mode is excited. The control parameters are the magnetic Reynolds number of the mean flow, the coefficient measuring the induction effect α, and the type of boundary conditions. We show that using realistic values of α, the observed critical magnetic Reynolds number, Rmc 32, can be reached easily with ferromagnetic boundary conditions. We conjecture that the dynamo action achieved in this experiment may not be related to the turbulence in the bulk of the flow, but rather to the α effect induced by the impellers. © 2008 The American Physical Society.