Document Type

Article

Publication Date

4-27-2005

Publication Title

Physical Review Letters

Abstract

We present a three-pronged numerical approach to the dynamo problem at low magnetic Prandtl numbers PM. The difficulty of resolving a large range of scales is circumvented by combining direct numerical simulations, a Lagrangian-averaged model and large-eddy simulations. 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 PM=1 down to PM=10−2, (ii) the critical magnetic Reynolds number increases sharply with P−1M as turbulence sets in and then it saturates, and (iii) in the linear growth phase, unstable magnetic modes move to smaller scales as PM is decreased. Then the dynamo grows at large scales and modifies the turbulent velocity fluctuations.

DOI

10.1103/PhysRevLett.94.164502

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