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arXiv · 2110.15807

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

Felix Schindler·Sven Eckert·Till Zürner·Jörg Schumacher·Tobias Vogt
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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 $\leq 5 \times 10^9$ and Prandtl numbers of $0.025~\leq~Pr~\leq ~0.033$. 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 $Nu\propto Ra^{\beta}$ 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.

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Felix Schindler, Sven Eckert, Till Zürner, Jörg Schumacher, Tobias Vogt. 2021-10-29. Collapse of Coherent Large Scale Flow in Strongly Turbulent Liquid Metal Convection. https://doi.org/10.1103/physrevlett.128.164501

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