The large-scale footprint in small-scale Rayleigh-Bénard turbulence

Turbulent convection systems are known to give rise to prominent large-scale circulation. At the same time, the 'background' (or 'small-scale') turbulence is also highly relevant and e.g. carries the majority of the heat transport in the bulk of the flow. Here, we investigate how the small-scale turbulence is interlinked with the large-scale flow organization of Rayleigh-Bénard convection. Our results are based on a numerical simulation at Rayleigh number in a large aspect ratio cell to ensure a distinct scale separation. We extract local magnitudes and wavenumbers of small-scale turbulence and find significant correlation of large-scale variations in these quantities with the large-scale signal. Most notably, we find stronger temperature fluctuations and increased small-scale transport (by about 10Â % of the global Nusselt number) in plume impacting regions and opposite trends in the plume emitting counterparts. This concerns wall distances up to (thermal boundary layer thickness). Local wavenumbers are generally found to be higher on the plume emitting side compared to the impacting one. A second independent approach by means of conditional averages confirmed these findings and yields additional insight into the large-scale variation of small-scale properties. Our results have implications for the modelling of small-scale turbulence.