On the role of the Prandtl number in convection driven by heat sources and sinks

Abstract

We report on a numerical study of turbulent convection driven by a combination of internal heat sources and sinks. Motivated by a recent experimental realisation (Lepot et al. 2018), we focus on the situation where the cooling is uniform, while the internal heating is localised near the bottom boundary, over approximately one tenth of the domain height. We obtain scaling laws $Nu\sim R{a}^{\gamma }P{r}^{\chi }$ for the heat transfer as measured by the Nusselt number $Nu$ expressed as a function of the Rayleigh number $Ra$ and the Prandtl number $Pr$. After confirming the experimental value $\gamma \approx 1/2$ for the dependence on $Ra$, we identify several regimes of dependence on $Pr$. For a stress-free bottom surface and within a range as broad as $Pr\in [0.003,10]$, we observe the exponent $\chi \approx 1/2$, in agreement with Spiegel's mixing length theory. For a no-slip bottom surface we observe a transition from $\chi \approx 1/2$ for $Pr\le 0.04$ to $\chi \approx 1/6$ for $Pr\ge 0.04$, in agreement with scaling predictions by Bouillaut et al. The latter scaling regime stems from heat accumulation in the stagnant layer adjacent to a no-slip bottom boundary, which we characterise by comparing the local contributions of diffusive and convective thermal fluxes.

11 pages, 3 figures

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Cited by in corpus (7)

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• Velocity-informed upper bounds on the convective heat transport induced by internal heat sources and sinks
• A direct derivation of the Gent-McWilliams/Redi diffusion tensor from quasi-geostrophic dynamics
• Dynamics and Scaling of Internally Cooled Convection
• Centrifugal instability of Taylor-Couette flow in stratified and diffusive fluids
• Ultimate regimes in horizontal and internally heated convection