Why, how and when MHD turbulence at low Rm becomes three-dimensional

Alban Potherat, Rico Klein

    Research output: Contribution to journalArticle

    25 Citations (Scopus)
    25 Downloads (Pure)

    Abstract

    Magnetohydrodynamic (MHD) turbulence at low magnetic Reynolds number is experimentally investigated by studying a liquid metal flow in a cubic domain. We focus on the mechanisms that determine whether the flow is quasi-two-dimensional, three-dimensional or in any intermediate state. To this end, forcing is applied by injecting a DC current I through one wall of the cube only, to drive vortices spinning along the magnetic field. Depending on the intensity of the externally applied magnetic field, these vortices extend part or all of the way through the cube. Driving the flow in this way allows us to precisely control not only the forcing intensity but also its dimensionality. A comparison with the theoretical analysis of this configuration singles out the influences of the walls and of the forcing on the flow dimensionality. Flow dimensionality is characterised in several ways. First, we show that when inertia drives three-dimensionality, the velocity near the wall where current is injected scales as Ub∼I2/3. Second, we show that when the distance lz over which momentum diffuses under the action of the Lorentz force (Sommeria & Moreau, J. Fluid Mech., vol. 118, 1982, pp. 507–518) reaches the channel width h, the velocity near the opposite wall Ut follows a similar law with a correction factor (1−h/lz) that measures three-dimensionality. When lz
    Original languageEnglish
    Pages (from-to)168-205
    JournalJournal of Fluid Mechanics
    Volume761
    Issue numberdecember 2014
    Early online date18 Nov 2014
    DOIs
    Publication statusPublished - 25 Dec 2014

      Fingerprint

    Keywords

    • MHD and electrohydrodynamics
    • MHD turbulence

    Cite this