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Home > Seminars and Workshops > Past seminars, PhD & HDR defense > 2018 > Séminaires 2018 > Le jeudi 5 juillet 2018 à 10h30

Le jeudi 5 juillet 2018 à 10h30

Salle de réunion Jean Lascoux, aile 0, RdC

10h30: accueil café

11h00: Séminaire: "Turbulent dynamos: from laboratory observations to numerical modeling"
par : Nicolas Plihon (Laboratoire de Physique, ENS de Lyon & CNRS)

The dynamo instability is a generic process converting kinetic energy in magnetic energy, which is at the origin of the magnetic fields of most astrophysical bodies. I will first give a review of the experimental observations of dynamos regimes observed in the von-Karman Sodium dynamo experiment (CNRS, CEA, ENS de Lyon, ENS de Paris) in which dynamo action has been achieved in turbulent flows of liquid sodium driven by the counter rotation of soft-iron impellers in a cylindrical vessel. Interestingly, the observed dynamo mode is not the one predicted from computations using the time-averaged flow and is origin rely on turbulent processes. Moreover, despite the highly turbulent features of the flow, the dynamo magnetic field displays regimes understood from low dimensional dynamics (and similar to the chaotic reversals of the Earth magnetic field or to the regular oscillations of the Sun) [1]. I will then present recent numerical results reproducing most of the experimental features [2]. Our model involve direct numerical simulations of the MHD equations with immersed boundary methods, which adequately model the influence of the rotating impellers on the dynamo instability.

[1] Monchaux et al., Phys. Fluids 21, 035108 (2009)

[2] Kreuzahler et al., Phys. Rev. Lett. 199, 2345901 (2017)

Tutelles : CNRS Ecole Polytechnique Sorbonne Université Université Paris Sud Observatoire de Paris Convention : CEA
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