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Article Dans Une Revue Physical Review Fluids Année : 2019

Inverse cascade of hybrid helicity in BΩ-MHD turbulence

Résumé

We investigate the impact of a solid-body rotation Ω0 on the large-scale dynamics of an incompressible magnetohydrodynamic turbulent flow in presence of a background magnetic field B0 and at low Rossby number. Three-dimensional direct numerical simulations are performed in a periodic box, at unit magnetic Prandtl number and with a forcing at intermediate wave number kf=20. When Ω0 is aligned with B0 (i.e., θ≡ˆ(Ω0,B0)=0), inverse transfer is found for the magnetic spectrum at k0 and becomes weak when θ≥35∘. These properties are understood as the consequence of an inverse cascade of hybrid helicity which is an inviscid/ideal invariant of this system when θ=0. Hybrid helicity emerges, therefore, as a key element for understanding rotating dynamos. Implication of these findings on the origin of the alignment of the magnetic dipole with the rotation axis in planets and stars is discussed.

Dates et versions

hal-02272441 , version 1 (27-08-2019)

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Mélissa Menu, Sébastien Galtier, Ludovic Petitdemange. Inverse cascade of hybrid helicity in BΩ-MHD turbulence. Physical Review Fluids, 2019, 4, pp.073701. ⟨10.1103/PhysRevFluids.4.073701⟩. ⟨hal-02272441⟩
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