Experimental investigations on turbulent Taylor-Couette flows in very wide gaps (part 2)

极宽间隙中泰勒-库埃特湍流的实验研究（第 2 部分）

• 批准号: 422002662
• 负责人: Professor Dr.-Ing. Christoph Egbers
• 金额: --
• 依托单位: Lehrstuhl Aerodynamik und Strömungslehre
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/422002662?language=en
• 关键词: Experimental; investigations; turbulent; Taylor; Couette

The proposed work is the second phase of the project ‘Experimental investigation of turbulent Taylor-Couette (TC) in very wide gaps’. The objectives of this work are divided into two groups: one concentrating on the flow in the centrifugally unstable regime and based on the scientific open questions posed in the project's first phase, and the other researching the flow in the centrifugally stable regime, specifically the quasi-Keplerian flow (η²≤µ≤1), where this flow regime was not addressed in the project’s first phase. Here, the existing experimental apparatus (TvTCC) will be used in the first part to further analyze existing flow parameters. While a new system is proposed to be built with a larger geometry that allows measurements of the flow structures with significantly higher spatial and temporal resolution and direct torque measurements. The visualization of the very wide gap TC flow (η = 0.1) in the counter-rotating regime shows the existence of a variety of flow patterns, where some of these patterns are found to be unique to this geometry (e.g., Axial Columnar vortex, Helical Columnar vortex, etc.). The mechanics responsible for this set of patterns are still an open question and will be addressed in this work. Moreover, the angular momentum transport dependence on the rotation rate in η = 0.1 shows a maximum of transport for low counter-rotating rates, where the large-scale circulation (LSC) fulfills the whole gap and enhances the transport of the angular momentum flux. As counter-rotating rates increase, the LSC detaches from the outer cylinder wall due to the outer rotation stabilizing effect and leads to a decrease in momentum transport until it achieves a minimum. Unexpectedly, and for higher counter-rotating rates, the angular momentum transport starts to increase again, despite the apparently stabilizing effect of the outer cylinder rotation. The flow's space-time analysis indicates that the presence of inward-propagating patterns developed near the outer cylinder wall leads to this increase in angular momentum transport at high counter-rotating rates. Since these novel patterns arise in a centrifugally stable region, it is unclear what instability is responsible for them. The proposed work will focus on studying the dynamics of the outer boundary layers where these patterns appear and further studying the analogy between these patterns and the shear-induced superstructures that appear in other wall-bounded flows (pipe, channel, etc.). For TC flow in the centrifugal stable regime, numerous studies tried to find a subcritical hydrodynamic instability to bring turbulence into account. However, in the very wide-gap flow (η = 0.1), structures have been found that are assumed to contribute to the overall angular momentum transport. Further identification and quantification of these patterns are needed, in addition to the quantification of the global angular momentum transport for the flow in the centrifugally stable regime.

拟议的工作是“大间隙中湍流泰勒-库埃特（TC）的实验研究”项目的第二阶段。这项工作的目标分为两组：一组专注于离心不稳定状态下的流动，并基于项目第一阶段提出的科学开放问题，另一组研究离心稳定状态下的流动，特别是准开普勒流动（η²≤μ≤1），该流动状态在项目第一阶段并未得到解决。这里，第一部分将使用现有的实验装置（TvTCC）来进一步分析现有的流动参数。同时建议建立一个具有更大几何形状的新系统，允许以显着更高的空间和时间分辨率测量流动结构以及直接扭矩测量。反向旋转状态下的非常宽间隙 TC 流 (η = 0.1) 的可视化表明存在多种流动模式，其中一些模式被发现是该几何形状所独有的（例如，轴向柱状涡流、螺旋柱状涡流等）。负责这组模式的机制仍然是一个悬而未决的问题，将在这项工作中得到解决。此外，角动量输运对旋转速率的依赖性在 η = 0.1 时显示出低反向旋转速率下的输运最大值，其中大尺度环流 (LSC) 满足了整个间隙并增强了角动量通量的输运。随着反向旋转速率增加，LSC 由于外旋转稳定效应而与外圆柱壁分离，导致动量传输减少，直至达到最小值。出乎意料的是，对于更高的反向旋转速率，角动量传输再次开始增加，尽管外圆柱体旋转具有明显的稳定作用。流动的时空分析表明，在外圆柱壁附近形成的向内传播模式的存在导致高反向旋转速率下角动量传输的增加。由于这些新颖的模式出现在离心稳定区域，因此尚不清楚造成它们的不稳定性是什么。拟议的工作将重点研究这些模式出现的外边界层的动力学，并进一步研究这些模式与其他壁面流动（管道、通道等）中出现的剪切引起的上部结构之间的类比。对于离心稳定状态下的 TC 流动，大量研究试图找到亚临界流体动力学不稳定性以将湍流考虑在内。然而，在非常宽间隙的流动（η = 0.1）中，已经发现了被认为有助于整体角动量传输的结构。除了量化离心稳定状态下流动的整体角动量传输之外，还需要进一步识别和量化这些模式。