Experimental Analysis of Turbulent Superstructures in Thermal Convection by Time-Resolved Lagrangian Particle Tracking up to Very High Rayleigh Numbers

通过高达极高瑞利数的时间分辨拉格朗日粒子跟踪对热对流中的湍流上层结构进行实验分析

• 批准号: 429432497
• 负责人: Dr. Johannes Bosbach
• 金额: --
• 依托单位: Institut für Aeordynamik und Strömungstechnik (IAS)
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/429432497?language=en
• 关键词: Experimental; Analysis; Turbulent; Superstructures; Thermal

With this proposal, we aim at application of several innovative measurement techniques to capturing turbulent superstructures (TSS) in Rayleigh-Bénard convection (RBC) in the classical turbulent regime and the ultimate state. Combination of the “Shake-The-Box” (STB) Lagrangian Particle Tracking method for densely seeded flows with long-lived microscopic soap bubbles as tracer particles, the data assimilation tool FlowFit and Temperature-Sensitive Paints (TSP), large scale measurements with high spatial and temporal resolution shall be enabled. The generated data will help improving the understanding of complex phenomena such as interactions between turbulent superstructures or large scale circulations (LSC), thermal plumes and turbulent background fluctuations by directly observing their dynamic interplay. Two different samples shall be addressed. The lower Ra (< 2·10^8) are accessed with a convection cell using water as working fluid. It has a quadratic horizontal section and a variable aspect ratio in the range of 4-10. Further, a cuboidal convection cell with a longitudinal aspect ratio variable between 5 and 10 will be used. It shall be operated within the ‘U-Boot’ of the Max-Planck-Institute for Dynamics and Self-Organization, employing pressurized Sulphur-Hexafluoride as working fluid. This procedure allows to access Rayleigh numbers up to 5·10^13. In specific, the following Goals and research questions shall be addressed with this proposal.Goals:1. Generate and observe turbulent superstructures in RBC under laboratory conditions 2. Establish STB / FlowFit and TSP as an experimental toolbox to study Lagrangian and Eulerian flow structures and statistics in RBC3. Extend the STB / FlowFit methodology to determine 3D temperature fields in parallel to the velocity fields by using temperature-sensitive particles4. Study turbulent RBC at moderately large aspect ratios (4..10) up to very high Ra (~10^13)Research questions:1. How do the generated TSS scale with the Rayleigh-number?2. How does the morphology and dynamics of the large scale flow structures change upon transition from LSC to TSS, i.e. with increasing aspect ratio?3. What are the mechanisms driving the dynamic interplay between small and large scale coherent flow / superstructures, such as thermal plumes, LSC and TSS or adjacent LSC? 4. How far does the actual geometry of the lateral confinement (rectangular, quadratic, circular) impact on the dimension and lateral arrangement of turbulent superstructures?5. How are the large scale flow structures (LSC / TSS) linked to the patterns observed just above the onset of convection?

有了这个建议，我们的目标是应用几种创新的测量技术来捕捉在瑞利-贝纳德对流（RBC）在经典的湍流状态和最终状态的湍流超结构（TSS）。将“摇箱”（STB）拉格朗日粒子跟踪方法与长效微观肥皂泡（作为示踪粒子）、数据同化工具FlowFit和温度敏感涂料（TSP）相结合，用于密集播种流，应启用具有高空间和时间分辨率的大规模测量。生成的数据将有助于提高对复杂现象的理解，例如湍流上层结构或大尺度环流（LSC），热羽流和湍流背景波动之间的相互作用，直接观察它们的动态相互作用。应处理两个不同的样本。较低的Ra（< 2·10^8）通过使用水作为工作流体的对流单元访问。它有一个方形的水平截面和一个可变的长宽比在4-10的范围内。此外，将使用纵向纵横比在5和10之间变化的立方形对流单元。它应在马克斯-普朗克动力学和自组织研究所的“U形罩”内运行，采用加压六氟化硫作为工作流体。这个过程允许访问瑞利数高达5·10^13。具体而言，本建议书将涉及以下目标和研究问题。目标：1.在实验室条件下生成并观察红细胞中的湍流超结构2.建立STB / FlowFit和TSP作为实验工具箱，以研究RBC 3中的拉格朗日和欧拉流结构和统计。扩展STB / FlowFit方法，通过使用温度敏感粒子4来确定与速度场平行的3D温度场。研究中等大纵横比下的湍流RBC（4.. 10)高达非常高的Ra（~10^13）研究问题：1.生成的TSS如何随瑞利数缩放？2.当从LSC过渡到TSS时，即随着纵横比的增加，大尺度流动结构的形态和动力学是如何变化的？3.驱动小尺度和大尺度相干流/超结构（如热羽流、LSC和TSS或邻近LSC）之间动态相互作用的机制是什么？4.横向约束的实际几何形状（矩形、方形、圆形）对紊流上层结构的尺寸和横向排列有多大的影响？5.大尺度流动结构（LSC / TSS）是如何与对流开始时观察到的模式联系起来的？