Investigation of the dynamics of large-scale circulation patterns in turbulent convection cells at very large aspect ratios with direct numerical simulations and experiments in compressed sulfur hexafluoride

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Many turbulent convection processes in nature and technology are present in extended layers or boxes and show hierarchies of regular ordered flow patterns although the corresponding Rayleigh and Reynolds numbers suggest a fully developed turbulence. In this project we want to study this spatio-temporal dynamics of large-scale structure formation in detail. Therefore, experiments with compressed sulfur hexafluoride will be combined with massively parallel direct numerical simulations based on a spectral element method. Both approaches will allow for convection studies in very large aspect ratio systems at Rayleigh numbers that were not accessible before. The analyses will clarify if such large-scale circulation patterns are relics persisting all the way from the onset of convection and the weakly nonlinear regime into the full turbulent regime. We want to identify the time scales on which the patterns evolve and investigate their Rayleigh number dependence. The experiment allows us to study the robustness of the circulation patterns with respect to non-Boussinesq effects. Based on the simulations, we want to develop amplitude models which can describe the patterns by means of a few dominant degrees of freedom giving rise to the possibility of a control of these patterns in technological applications.