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Numerical investigation of quasistatic magnetoconvection with an imposed horizontal magnetic field

Michael A. Calkins1,*, Talal AlRefae1, Angel Hernandez1, Ming Yan1, and Stefano Maffei2

  • 1Department of Physics, University of Colorado, Boulder, Colorado 80309, USA
  • 2Institute of Geophysics, ETH Zurich, Sonneggstrasse 5, 8092 Zürich, Switzerland

  • *michael.calkins@colorado.edu

Phys. Rev. Fluids 8, 123501 – Published 11 December, 2023

DOI: https://doi.org/10.1103/PhysRevFluids.8.123501

Abstract

Quasistatic Rayleigh-Bénard convection with an imposed horizontal magnetic field is investigated numerically for Chandrasekhar numbers up to Q=106 with stress-free boundary conditions. Both Q and the Rayleigh number (Ra) are varied to identify the various dynamical regimes that are present in this system. We find three primary regimes: (i) a two-dimensional (2D) regime in which the axes of the convection rolls are oriented parallel to the imposed magnetic field; (ii) an anisotropic three-dimensional (3D) regime; and (iii) a mean flow regime characterized by a large scale horizontal flow directed transverse to the imposed magnetic field. The transition to 3D dynamics is preceded by a series of 2D transitions in which the number of convection rolls decreases as Ra is increased. For sufficiently large Q, there is an eventual transition to two rolls just prior to the 2D-3D transition. The 2D-3D transition occurs when inertial forces become comparable to the Lorentz force, i.e., when Q/Re=O(1); 2D, magnetically constrained states persist when Q/ReO(1). Within the 2D regime, we find heat and momentum transport scalings that are consistent with the hydrodynamic asymptotic predictions of Chini and Cox [Phys. Fluids 21, 083603 (2009)]: the Nusselt number (Nu) and Reynolds number (Re) scale as NuRa1/3 and ReRa2/3, respectively. For Q=106, we find that the scaling behavior of Nu and Re breaks down at large values of Ra due to a sequence of bifurcations and the eventual manifestation of mean flows.

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