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

湍流Rayleigh-Bénard（RB）对流是描述地球大气和海洋中的流动和对流热输运现象的一种典型模式。除了这些地球物理流动，RB模型也用于研究室内流动或液体热储层中热分层的维持。很长一段时间以来，科学几乎完全集中在预测通过从下面加热和从上面冷却的流体层的全球和时间平均热通量上。然而，目前的问题，如固体颗粒或气溶胶在大气中的分散或室内环境中的空气的自然混合，需要在这种对流驱动的流动的大尺度流动模式的知识。在本研究项目中，我们希望通过实验研究完全湍流RB对流中的全球环流，特别关注纵横比Γ（试验段水平和垂直范围之间的比率）对发展流型的影响。类似于自然界和工程中大多数对流驱动的流动，我们将重点关注Γ=2和Γ=10之间的“大”展弦比。我们将使用所谓的“伊尔梅瑙桶”，这是TU伊尔梅瑙空气动力学系的一个大规模RB实验（直径：7.1米，高度：0.2米）。6.3 m）作为试验段。 在该设备中可以实现高达Ra= 100的瑞利数。采用拉格朗日粒子跟踪法对充气试验段的流场进行了测量，并对不同展弦比下的流态进行了分析。拟议的实验工作的特别优势在于一个显着更长的观察时间相比，等效的直接数值模拟。这也导致统计预测精度的显著提高。除了回答有关流型的性质及其典型寿命的问题外，该项目还将研究病毒或污染物负载的气溶胶如何在湍流对流中传播，以及这如何取决于流型。

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.