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Abstract: We report an experimental investigation on the influence of an externalmagnetic field on forced 3D turbulence of liquid gallium in a closed vessel. Weobserve an exponential damping of the turbulent velocity fluctuations as afunction of the interaction parameter N ratio of Lorentz force over inertialterms of the Navier-Stokes equation. The flow structures develop someanisotropy but do not become bidimensional. From a dynamical viewpoint, thedamping first occurs homogeneously over the whole spectrum of frequencies. Forlarger values of N, a very strong additional damping occurs at the highestfrequencies. However, the injected mechanical power remains independent of theapplied magnetic field. The simultaneous measurement of induced magnetic fieldand electrical potential differences shows a very weak correlation betweenmagnetic field and velocity fluctuations. The observed reduction of thefluctuations is in agreement with a previously proposed mechanism for thesaturation of turbulent dynamos and with the order of magnitude of the VonKarman Sodium dynamo magnetic field.



Autor: Basile Gallet, Michael Berhanu, Nicolas Mordant

Fuente: https://arxiv.org/



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