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?

通过这项建议，我们的目标是应用几种创新的测量技术来捕获经典湍流状态和“Shake-The-Box”（STB）组合中瑞利-贝纳德对流（RBC）中的湍流上层结构（TSS）。 ）以长寿命微观肥皂泡作为示踪粒子的密集种子流的拉格朗日粒子追踪方法，数据同化工具 FlowFit 和温度敏感涂料（TSP）、具有高空间和时间分辨率的大规模测量将有助于提高对复杂现象的理解，例如湍流上层结构或大规模环流（LSC）、热羽流和湍流之间的相互作用。通过直接观察它们的动态相互作用来解决背景波动。应使用水作为工作流体来获取较低的 Ra (< 2·10^8)。二次水平截面和 4-10 范围内的可变纵横比此外，将使用纵向纵横比可变在 5 到 10 之间的立方体对流单元，它应在 Max 的“U-Boot”范围内运行。 -普朗克动力学和自组织研究所，采用加压六氟化硫作为工作流体，该过程允许获得高达 5·10^13 的瑞利数。具体而言，本提案应解决以下目标和研究问题。 目标：1. 在实验室条件下生成并观察 RBC 中的湍流上层结构 2. 建立 STB / FlowFit 和 TSP 作为研究拉格朗日和欧拉流动结构和统计的实验工具箱在 RBC3 中，扩展 STB / FlowFit 方法，通过使用温度敏感粒子研究湍流 RBC 来确定与速度场平行的 3D 温度场。中等大的长宽比（4..10）到非常高的Ra（~10^13）研究问题：1. 生成的TSS如何与瑞利数进行缩放？2．从 LSC 过渡到 TSS 时，流动结构会发生变化，即随着纵横比的增加，驱动小型和大规​​模相干流/上部结构（例如热羽流、LSC 和 TSS 或相邻 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、二次形、圆形）对湍流上层结构的尺寸和横向排列的影响有多大？ 5. 大规模流动结构（LSC / TSS）如何与观察到的模式相关联？高于对流开始？