Wall modes in magnetoconvection at high Hartmann numbers

Abstract

Three-dimensional turbulent magnetoconvection at a Rayleigh number of $Ra=10^7$ in liquid gallium at a Prandtl number $Pr=0.025$ is studied in a closed square cell for very strong external vertical magnetic fields $B_0$ in direct numerical simulations which apply the quasistatic approximation. As $B_0$ or equivalently the Hartmann number $Ha$ are increased, the convection flow that is highly turbulent in the absence of magnetic fields crosses the Chandrasekhar linear stability limit for which thermal convection is ceased in an infinitely extended layer and which can be assigned with a critical Hartmann number $H{a}_{\mathrm{c}}$. Similar to rotating Rayleigh-Bénard convection, our simulations reveal subcritical sidewall modes that maintain a small but finite convective heat transfer for $Ha>H{a}_{\mathrm{c}}$. We report a detailed analysis of the complex two-layer structure of these wall modes, their extension into the cell interior and a resulting sidewall boundary layer composition that is found to scale with the Shercliff layer thickness.

References in corpus (3)

• Global and local statistics in turbulent convection at low Prandtl numbers
• The role of Stewartson and Ekman layers in turbulent rotating Rayleigh-Bénard convection
• Heat and momentum transfer for magnetoconvection in a vertical external magnetic field

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• Free-fall velocities and heat transport enhancement in liquid metal magneto-convection
• Velocimetry in rapidly rotating convection: spatial correlations, flow structures and length scales
• Wall mode dynamics and transition to chaos in magnetoconvection with a vertical magnetic field
• Refined mean field model of heat and momentum transfer in magnetoconvection
• Scaling relations in quasi-static magnetoconvection with a strong vertical magnetic field
• Effects of strong fringing magnetic fields on turbulent thermal convection
• Rapidly Rotating Wall-Mode Convection
• Thermoelectric Precession in Turbulent Magnetoconvection