Abstract
We report the observation of superstructures, i.e., very large-scale and long living coherent structures in highly turbulent Rayleigh-Bénard convection up to Rayleigh . We perform direct numerical simulations in horizontally periodic domains with aspect ratios up to . In the considered number regime the thermal superstructures have a horizontal extend of six to seven times the height of the domain and their size is independent of . Many laboratory experiments and numerical simulations have focused on small aspect ratio cells in order to achieve the highest possible . However, here we show that for very high integral quantities such as the Nusselt number and volume averaged Reynolds number only converge to the large aspect ratio limit around , while horizontally averaged statistics such as standard deviation and kurtosis converge around , the integral scale converges around , and the peak position of the temperature variance and turbulent kinetic energy spectra only converge around .
- Received 8 August 2017
DOI:https://doi.org/10.1103/PhysRevFluids.3.041501
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