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The effect of velocity shear on dynamo action due to rotating convection

Published online by Cambridge University Press:  01 February 2013

D. W. Hughes  and
M. R. E. Proctor
D. W. Hughes*
Affiliation:
Department of Applied Mathematics, University of Leeds, Leeds LS2 9JT, UK
M. R. E. Proctor
Affiliation:
Centre for Mathematical Sciences, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, UK
*
†Email address for correspondence: d.w.hughes@leeds.ac.uk
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Abstract

Recent numerical simulations of dynamo action resulting from rotating convection have revealed some serious problems in applying the standard picture of mean field electrodynamics at high values of the magnetic Reynolds number, and have thereby underlined the difficulties in large-scale magnetic field generation in this regime. Here we consider kinematic dynamo processes in a rotating convective layer of Boussinesq fluid with the additional influence of a large-scale horizontal velocity shear. Incorporating the shear flow enhances the dynamo growth rate and also leads to the generation of significant magnetic fields on large scales. By the technique of spectral filtering, we analyse the modes in the velocity that are principally responsible for dynamo action, and show that the magnetic field resulting from the full flow relies crucially on a range of scales in the velocity field. Filtering the flow to provide a true separation of scales between the shear and the convective flow also leads to dynamo action; however, the magnetic field in this case has a very different structure from that generated by the full velocity field. We also show that the nature of the dynamo action is broadly similar irrespective of whether the flow in the absence of shear can support dynamo action.

JFM classification

MHD and Electrohydrodynamics: Dynamo theory MHD and Electrohydrodynamics: MHD turbulence

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Type
Papers
Information
Journal of Fluid Mechanics , Volume 717 , 25 February 2013 , pp. 395 - 416
Copyright
©2013 Cambridge University Press

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Hughes and M. R. E. Proctor supplementary movie

Temporal evolution of $B_x$ at the upper boundary for $U_0 =1000$

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