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Article Dans Une Revue Physical Review Letters Année : 2005

Numerical study of dynamo action at low magnetic Prandtl numbers

Résumé

We present a three--pronged numerical approach to the dynamo problem at low magnetic Prandtl numbers $P_M$. The difficulty of resolving a large range of scales is circumvented by combining Direct Numerical Simulations, a Lagrangian-averaged model, and Large-Eddy Simulations (LES). The flow is generated by the Taylor-Green forcing; it combines a well defined structure at large scales and turbulent fluctuations at small scales. Our main findings are: (i) dynamos are observed from $P_M=1$ down to $P_M=10^{-2}$; (ii) the critical magnetic Reynolds number increases sharply with $P_M^{-1}$ as turbulence sets in and then saturates; (iii) in the linear growth phase, the most unstable magnetic modes move to small scales as $P_M$ is decreased and a Kazantsev $k^{3/2}$ spectrum develops; then the dynamo grows at large scales and modifies the turbulent velocity fluctuations.
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Dates et versions

hal-00133225 , version 1 (19-08-2023)

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Yannick Ponty, P. D. Mininni, D. C. Montgomery, Jean-François Pinton, Hélène Politano, et al.. Numerical study of dynamo action at low magnetic Prandtl numbers. Physical Review Letters, 2005, 94, pp.164502. ⟨10.1103/PhysRevLett.94.164502⟩. ⟨hal-00133225⟩
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