Combined measurement of velocity and temperature in liquid metal convection

Abstract

Combined measurements of velocity components and temperature in a turbulent Rayleigh-Bénard convection flow at a low Prandtl number of $Pr=0.029$ and Rayleigh numbers between $10^6\le Ra\le 6\times 10^7$ are conducted in a series of experiments with durations of more than a thousand free-fall time units. Multiple crossing ultrasound beam lines and an array of thermocouples at mid-height allow for a detailed analysis and characterization of the complex three-dimensional dynamics of the single large-scale circulation (LSC) roll in the cylindrical convection cell of unit aspect ratio which is filled with the liquid metal alloy GaInSn. We measure the internal temporal correlations of the complex large-scale flow and distinguish between short-term oscillations associated with a sloshing motion in the mid-plane as well as varying orientation angles of the velocity close to the top/bottom plates and the slow azimuthal drift of the mean orientation of the roll as a whole that proceeds on an up to a hundred times slower time scale. The coherent LSC drives a vigorous turbulence in the whole cell that is quantified by direct Reynolds number measurements at different locations in the cell. The velocity increment statistics in the bulk of the cell displays characteristic properties of intermittent small-scale fluid turbulence. We also show that the impact of the symmetry-breaking large-scale flow persists to small-scale velocity fluctuations thus preventing the establishment of fully isotropic turbulence in the cell centre. Reynolds number amplitudes depend sensitively on beam line position in the cell such that different definitions have to be compared. The global momentum and heat transfer scalings with Rayleigh number are found to agree with those of direct numerical simulations and other laboratory experiments.

References in corpus (7)

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• Comparison between two and three dimensional Rayleigh-Bénard convection
• Origin of the Temperature Oscillation in Turbulent Thermal Convection
• Boundary layer structure in turbulent Rayleigh-Benard convection
• Global and local statistics in turbulent convection at low Prandtl numbers
• Jump Rope Vortex in Liquid Metal Convection
• Transitional boundary layers in low-Prandtl-number convection

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• Convective mesoscale turbulence at very low Prandtl numbers
• Free-fall velocities and heat transport enhancement in liquid metal magneto-convection
• Flow states and heat transport in liquid metal convection
• Refined mean field model of heat and momentum transfer in magnetoconvection
• Oscillatory large-scale circulation in liquid-metal thermal convection and its structural unit
• Laboratory model of electrovortex flow with thermal gradients, for liquid metal batteries
• Turbulent mesoscale convection in the Boussinesq limit and beyond
• Synchronizing the helicity of Rayleigh-Bénard convection by a tide-like electromagnetic forcing
• Thermoelectric Precession in Turbulent Magnetoconvection