Thermoelectric precession in turbulent magnetoconvection

• Published in: Journal of fluid mechanics Vol. 930
• Main Authors: Xu, Yufan, Horn, Susanne, Aurnou, Jonathan M.
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 10.01.2022
• Subjects: Boundary conditions; Convective flow; Direction; Experiments; Gallium; Heat transfer; JFM Papers; Laboratories; Liquid metals; Magnetic field; Magnetic fields; Magnetohydrodynamic turbulence; Magnetohydrodynamics; Metals; Mixing; Mixing processes; Planetary interiors; Precession; Temperature; Thermoelectricity; Torque; magneto convection; geodynamo
• ISSN: 0022-1120; 1469-7645; 1469-7645
• DOI: 10.1017/jfm.2021.880

We present laboratory measurements of the interaction between thermoelectric currents and turbulent magnetoconvection. In a cylindrical volume of liquid gallium heated from below and cooled from above and subject to a vertical magnetic field, it is found that the large-scale circulation (LSC) can undergo a slow axial precession. Our experiments demonstrate that this LSC precession occurs only when electrically conducting boundary conditions are employed, and that the precession direction reverses when the axial magnetic field direction is flipped. A thermoelectric magnetoconvection (TEMC) model is developed that successfully predicts the zeroth-order magnetoprecession dynamics. Our TEMC magnetoprecession model hinges on thermoelectric current loops at the top and bottom boundaries, which create Lorentz forces that generate horizontal torques on the overturning large-scale circulatory flow. The thermoelectric torques in our model act to drive a precessional motion of the LSC. This model yields precession frequency predictions that are in good agreement with the experimental observations. We postulate that thermoelectric effects in convective flows, long argued to be relevant in liquid metal heat transfer and mixing processes, may also have applications in planetary interior magnetohydrodynamics.