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Turbulent Rayleigh–Bénard convection in an annular cell
Published online by Cambridge University Press: 29 April 2019
Abstract
We report an experimental study of turbulent Rayleigh–Bénard (RB) convection in an annular cell of water (Prandtl number $Pr=4.3$) with a radius ratio $\unicode[STIX]{x1D702}\simeq 0.5$. Global quantities, such as the Nusselt number $Nu$ and the Reynolds number $Re$, and local temperatures were measured over the Rayleigh range $4.2\times 10^{9}\leqslant Ra\leqslant 4.5\times 10^{10}$. It is found that the scaling behaviours of $Nu(Ra)$, $Re(Ra)$ and the temperature fluctuations remain the same as those in the traditional cylindrical cells; both the global and local properties of turbulent RB convection are insensitive to the change of cell geometry. A visualization study, as well as local temperature measurements, shows that in spite of the lack of the cylindrical core, there also exists a large-scale circulation (LSC) in the annular system: thermal plumes organize themselves with the ascending hot plumes on one side and the descending cold plumes on the opposite side. Near the upper and lower plates, the mean flow moves along the two circular branches. Our results further reveal that the dynamics of the LSC in this annular geometry is different from that in the traditional cylindrical cell, i.e. the orientation of the LSC oscillates in a narrow azimuthal angle range, and no cessations, reversals or net rotation were detected.
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Zhu et al. supplementary movie 1
The shadowgraph movie about the ascending plumes on one side of the annulus cell, and a schematic draw showing the large-scale circulation and the spatial distribution of thermal plumes at $Ra=4.5 imes10^{10}$. The purple frame marks the visualization window.
Zhu et al. supplementary movie 2
The shadowgraph movie about the cold plumes moving along the circular branches near the upper plate, and a schematic draw showing the large-scale circulation and the spatial distribution of thermal plumes at $Ra=4.5 imes10^{10}$. The purple frame marks the visualization window.
Zhu et al. supplementary movie 3
The shadowgraph movie about the descending plumes on the opposite side of the annulus cell, and a schematic draw showing the large-scale circulation and the spatial distribution of thermal plumes at $Ra=4.5 imes10^{10}$. The purple frame marks the visualization window.
Zhu et al. supplementary movie 4
The shadowgraph movie about the hot plumes moving along the circular branches near the lower plate, and a schematic draw showing the large-scale circulation and the spatial distribution of thermal plumes at $Ra=4.5 imes10^{10}$. The purple frame marks the visualization window.
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