Flow regimes of Rayleigh-Bénard convection in a vertical magnetic field

Abstract

The effects of a vertical static magnetic field on the flow structure and global transport properties of momentum and heat in liquid metal Rayleigh-Bénard convection are investigated. Experiments are conducted in a cylindrical convection cell of unity aspect ratio, filled with the alloy GaInSn at a low Prandtl number of $Pr=0.029$. Changes of the large-scale velocity structure with increasing magnetic field strength are probed systematically using multiple ultrasound Doppler velocimetry sensors and thermocouples for a parameter range that is spanned by Rayleigh numbers of $10^6\le Ra\le 6\times 10^7$ and Hartmann numbers of $Ha\le 1000$. Our simultaneous multi-probe temperature and velocity measurements demonstrate how the large-scale circulation is affected by an increasing magnetic field strength (or Hartmann number). Lorentz forces induced in the liquid metal first suppress the oscillations of the large-scale circulation at low $Ha$, then transform the one-roll structure into a cellular large-scale pattern consisting of multiple up- and downwellings for intermediate $Ha$, before finally expelling any fluid motion out of the bulk at the highest accessible $Ha$ leaving only a near-wall convective flow that persists even below Chandrasekhar's linear instability threshold. Our study thus proves experimentally the existence of wall modes in confined magnetoconvection. The magnitude of the transferred heat remains nearly unaffected by the steady decrease of the fluid momentum over a large range of Hartmann numbers. We extend the experimental global transport analysis to momentum transfer and include the dependence of the Reynolds number on the Hartmann number.

References in corpus (4)

• Rotations and cessations of the large-scale circulation in turbulent Rayleigh-Benard convection
• Origin of the Temperature Oscillation in Turbulent Thermal Convection
• Global and local statistics in turbulent convection at low Prandtl numbers
• Heat and momentum transfer for magnetoconvection in a vertical external magnetic field

Cited by in corpus (8)

• Free-fall velocities and heat transport enhancement in liquid metal magneto-convection
• Thermal boundary condition studies in large aspect ratio Rayleigh-Bénard convection
• 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
• Synchronizing the helicity of Rayleigh-Bénard convection by a tide-like electromagnetic forcing
• Thermoelectric Precession in Turbulent Magnetoconvection