| Autor: |
Bouillaut, Vincent, Lepot, Simon, Aumaître, Sébastien, Gallet, Basile |
| Předmět: |
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| Zdroj: |
Journal of Fluid Mechanics; 2/25/2019, Vol. 861, pN.PAG-N.PAG, 12p |
| Abstrakt: |
We report on the transition between two regimes of heat transport in a radiatively driven convection experiment, where a fluid gets heated up within a tunable heating length $\ell$ in the vicinity of the bottom of the tank. The first regime is similar to that observed in standard Rayleigh–Bénard experiments, the Nusselt number $Nu$ being related to the Rayleigh number $Ra$ through the power law $Nu\sim Ra^{1/3}$. The second regime corresponds to the 'ultimate' or mixing-length scaling regime of thermal convection, where $Nu$ varies as the square root of $Ra$. Evidence for these two scaling regimes has been reported in Lepot et al. (Proc. Natl Acad. Sci. USA , vol. 115, 2018, pp. 8937–8941), and we now study in detail how the system transitions from one to the other. We propose a simple model describing radiatively driven convection in the mixing-length regime. It leads to the scaling relation $Nu\sim (\ell /H)Pr^{1/2}Ra^{1/2}$ , where $H$ is the height of the cell and $Pr$ is the Prandtl number, thereby allowing us to deduce the values of $Ra$ and $Nu$ at which the system transitions from one regime to the other. These predictions are confirmed by the experimental data gathered at various $Ra$ and $\ell$. We conclude by showing that boundary layer corrections can persistently modify the Prandtl number dependence of $Nu$ at large $Ra$ , for $Pr\gtrsim 1$. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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