Transition to the ultimate regime in a radiatively driven convection experiment - CEA - Commissariat à l’énergie atomique et aux énergies alternatives Accéder directement au contenu
Article Dans Une Revue Journal of Fluid Mechanics Année : 2019

Transition to the ultimate regime in a radiatively driven convection experiment

Résumé

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 $Pr\gtrsim 1$ .

Dates et versions

cea-04344768 , version 1 (14-12-2023)

Identifiants

Citer

Vincent Bouillaut, Simon Lepot, Sébastien Aumaître, Basile Gallet. Transition to the ultimate regime in a radiatively driven convection experiment. Journal of Fluid Mechanics, 2019, 861, pp.R5. ⟨10.1017/jfm.2018.972⟩. ⟨cea-04344768⟩
10 Consultations
0 Téléchargements

Altmetric

Partager

Gmail Mastodon Facebook X LinkedIn More