Global flow patterns in turbulent Rayleigh-Bénard convection with variable aspect ratio

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Turbulent Rayleigh-Bénard (RB) convection is widely used as a canonical model to describe flow phenomena and convective heat transport in the Earth's atmosphere or in the oceans. In addition to these geophysical flows, the RB model is also used to study indoor flows or the maintenance of thermal stratification in liquid heat reservoirs. For a long time, science has focused almost exclusively on predicting the global and time-averaged heat flux through the fluid layer heated from below and cooled from above. However, current problems, such as the dispersion of solid particles or aerosols in the atmosphere or the natural mixing of air in indoor environments, require knowledge of the large-scale flow pattern in such convectively driven flows. In this research project, we want to experimentally study the global circulation in fully turbulent RB convection, with a special focus on the influence of the aspect ratio Γ (Γ - ratio between the horizontal and vertical extent of the test section) on the developing flow pattern. Analogous to the majority of convectively driven flows in nature and engineering, we will focus on "large" aspect ratios between Γ=2 and Γ=10. We will use the so-called "Barrel of Ilmenau", a large-scale RB experiment at the Department of Aerodynamics of the TU Ilmenau (diameter: 7.1 m, height: 0.2...6.3 m) as a test section. Rayleigh numbers up to Ra=〖10〗^12 can be achieved in this facility. The flow field in the air-filled test section will be measured using the Lagrangian Particle Tracking method and the flow pattern at different aspect ratios will be analyzed. The particular advantage of the proposed experimental work lies in a significantly longer observation time compared to equivalent direct numerical simulations. This also leads to a significant improvement of the statistical prediction accuracy. In addition to answering questions about the nature of flow patterns and their typical lifetime, this project will also investigate how virus- or pollutant-laden aerosols propagate in turbulent convection and how this depends on the flow pattern.