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arXiv · 2311.08327

Supergranule aggregation: a Prandtl number-independent feature of constant heat flux-driven convection flows

Philipp P. Vieweg
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Abstract

Supergranule aggregation, i.e., the gradual aggregation of convection cells to horizontally extended networks of flow structures, is a unique feature of constant heat flux-driven turbulent convection. In the present study, we address the question if this mechanism of self-organisation of the flow is present for any fluid. Therefore, we analyse three-dimensional Rayleigh-Bénard convection at a fixed Rayleigh number $\textrm{Ra} \approx 2.0 \times 10^{5}$ across $4$ orders of Prandtl numbers $\Pr \in \left[ 10^{-2}, 10^{2} \right]$ by means of direct numerical simulations in horizontally extended periodic domains with aspect ratio $Γ= 60$. Our study confirms the omnipresence of the mechanism of supergranule aggregation for the entire range of investigated fluids. Moreover, we analyse the effect of $\Pr$ on the global heat and momentum transport, and clarify the role of a potential stable stratification in the bulk of the fluid layer. The ubiquity of the investigated mechanism of flow self-organisation underlines its relevance for pattern formation in geophysical and astrophysical convection flows, the latter of which are often driven by prescribed heat fluxes.

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Philipp P. Vieweg. 2024-01-29. Supergranule aggregation: a Prandtl number-independent feature of constant heat flux-driven convection flows. https://doi.org/10.1017/jfm.2024.56

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