Collapse of Coherent Large Scale Flow in Strongly Turbulent Liquid Metal Convection

Abstract

The large-scale flow structure and the turbulent transfer of heat and momentum are directly measured in highly turbulent liquid metal convection experiments for Rayleigh numbers varied between $4\times 10^5$ and $\le 5\times 10^9$ and Prandtl numbers of $0.025\le Pr\le 0.033$. Our measurements are performed in two cylindrical samples of aspect ratios $\Gamma =$ diameter/height $=0.5$ and 1 filled with the eutectic alloy GaInSn. The reconstruction of the three-dimensional flow pattern by 17 ultrasound Doppler velocimetry sensors detecting the velocity profiles along their beamlines in different planes reveals a clear breakdown of coherence of the large-scale circulation for $\Gamma =0.5$. As a consequence, the scaling laws for heat and momentum transfer inherit a dependence on the aspect ratio. We show that this breakdown of coherence is accompanied with a reduction of the Reynolds number $Re$. The scaling exponent $\beta$ of the power law $Nu\propto R{a}^{\beta }$ crosses \FIN{eventually} over from $\beta =0.221$ to 0.124 when the liquid metal flow at $\Gamma =0.5$ reaches $Ra\gtrsim 2\times 10^8$ and the coherent large-scale flow is completely collapsed.

4 pages, 5 figures, 1 supplementary with 1 figure and 4 tables, 1 movie

References in corpus (3)

• Aspect ratio dependence of heat transfer and large-scale flow in turbulent convection
• Boundary layer structure in turbulent Rayleigh-Benard convection
• Free-fall velocities and heat transport enhancement in liquid metal magneto-convection

Cited by in corpus (9)

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• Synchronizing the helicity of Rayleigh-Bénard convection by a tide-like electromagnetic forcing
• Effects of conjugate heat transfer on large-scale flow structures in convection
• Turbulent convection in rotating slender cells
• Collective variables between large-scale states in turbulent convection