Robustness of heat-transfer in confined inclined convection at high-Prandtl-number

Abstract

We investigate the dependency of the magnitude of heat transfer in a convection cell as a function of its inclination by means of experiments and simulations. The study is performed with a working fluid of large Prandtl number, $Pr\simeq 480$, and at Rayleigh numbers $Ra\simeq 10^8$ and $Ra\simeq 5\times 10^8$ in a quasi-two-dimensional rectangular cell with unit aspect ratio. By changing the inclination angle ($\beta$) of the convection cell, the character of the flow can be changed from moderately turbulent, for $\beta =0^o$, to laminar and steady at $\beta =90^o$. The global heat transfer is found to be insensitive to the drastic reduction of turbulent intensity, with maximal relative variations of the order of $20\%$ at $Ra\simeq 10^8$ and $10\%$ at $Ra\simeq 5\times 10^8$, while the Reynolds number, based on the global root-mean- square velocity, is strongly affected with a decay of more than $85\%$ occurring in the laminar regime. We show that the intensity of the heat flux in the turbulent regime can be only weakly enhanced by establishing a large scale circulation flow by means of small inclinations. On the other hand, in the laminar regime the heat is transported solely by a slow large scale circulation flow which exhibits large correlations between the velocity and temperature fields. For inclination angles close to the transition regime in-between the turbulent-like and laminar state, a quasi-periodic heat-flow bursting phenomenon is observed.

11 pages, 9 figures (figure 2 here in low resolution)

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