Collapse of Coherent Large Scale Flow in Strongly Turbulent Liquid Metal Convection
Collapse of Coherent Large Scale Flow in Strongly Turbulent Liquid Metal Convection
Schindler, F.; Eckert, S.; Zürner, T.; Schumacher, J.; Vogt, T.
The largescale 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 threedimensional flow pattern by 17 ultrasound Doppler velocimetry sensors detecting the velocity profiles along their beamlines in different planes reveals a clear breakdown \FIN{of coherence} of the largescale 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 $Ra\gtrsim 2\times 10^8$ \FIN{and the coherent largescale flow is completely collapsed}.
Keywords: RayleighBenard Convection; liquid metal; low Pr; cylinder; Ultrasound Doppler Velocimetry; large scale flow structure
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Data publication: Collapse of Coherent Large Scale Flow in Strongly Turbulent …
ROBIS: 34142 HZDRprimary research data are used by this (Id 34082) publication

Physical Review Letters 128(2022)16, 164501
DOI: 10.1103/PhysRevLett.128.164501
Cited 15 times in Scopus
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Publ.Id: 34082