Thermal convection at high aspect ratio: The local distribution and the dynamics of dissipative processes

高纵横比下的热对流：耗散过程的局部分布和动力学

• 批准号: 390361628
• 负责人: Privatdozent Dr.-Ing. Ronald du Puits
• 金额: --
• 依托单位: Fachgebiet Aerodynamik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2017
• 资助国家: 德国
• 起止时间: 2016-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/390361628?language=en
• 关键词: Thermal; convection; aspect; ratio; local

The majority of geophysical and engineering processes incorporating convective heat transfer is characterized by a large ratio between the lateral and the vertical extent of the fluid layer. However, experimental and numerical work on thermal convection still focuses on configurations, where this ratio is rather small (equal or smaller than one). In particular, this is due to the fact that experiments achieving comparable high Rayleigh numbers must be very high and quite often this large height cannot be compensated by a respective width. Thus, it is actually not possible to fully evaluate phenomenological theories that are usually based one a one-dimensional model without lateral confinement. The applicants wish to contribute to overcome this by measurements of the heat flux and the thermal dissipation rate in an experiment meeting both, high aspect ratio (eight or larger) as well as high Rayleigh number (up to 10{12}). Unlike in the preceding project, they will focus in the new work on the dynamics of these two quantities. It is known from direct numerical simulations (DNS) by Scheel and Schumacher [J. Schumacher and J. D. Scheel. Extreme dissipation event due to plume collision in a turbulent convection cell. Phys. Rev. E 94, 043104 (2016)] that, in particular, the thermal dissipation rate fluctuates very strongly as well locally as in time. Now, this will be validated in an experiment for the first time. Because, measurements potentially cover a much longer “observation period” than comparable DNS, the statistical uncertainty of the measurement data will be significantly smaller In a second part, the applicants will pursue the following question: How representative are local and time-averaged measurement data at a single point (in turbulent Rayleigh-Bénard convection) for the entire respective horizontal plane. For aspect ratios smaller or equal to one, this problem is always studied in the past, and it is answered with “not representative”. For large aspect ratios, where the sidewall affects only a little outer fraction of the fluid layer, the applicants will answer this question by measurements of the thermal dissipation rate at various positions in multiple horizontal planes. These measurements will, thus, provide also the distribution of the local turbulent heat flux.

大多数地球物理和工程过程情感传热的特征在于流体层的横向和垂直范围之间的比例很高。但是，热转化的实验和数值工作仍然集中在配置上，在该配置中，该比率相当小（相等或小于一个）。特别是，这是由于实验获得可比的高雷利数必须很高，而且通常无法通过相对宽度来补偿该高度。这实际上是不可能完全评估通常基于一个一维模型而没有横向限制的现象学理论。在相遇的实验中，高纵横比（八个或更大）以及较高的雷利数（最高10 {12}），应用程序希望通过测量热通量和热耗散速率来克服这一点。与前面的项目不同，他们将重点关注这两个数量的动态的新工作。它是从Scheel和Schumacher的直接数值模拟（DNS）中知道的[J. Schumacher和J. D. Scheel。由于湍流连接电池中羽状碰撞而引起的极端耗散事件。物理。 E 94，043104（2016）]，特别是在及时的局部和本地强烈波动。现在，这将在实验中首次验证。因为，测量值可能涵盖了比可比DNS更长的“观察期”，因此测量数据的统计不确定性在第二部分中将显着较小，因此申请人将提出以下问题：在单个点处表示本地和时间平均的测量数据（在Turbulent Rayleigh-bénard连接中，对于整个相对平面）。对于较小或等于一个的宽高比，过去总是研究此问题，并以“不具有代表性”的方式回答。对于较大的纵横比，侧壁仅影响流体层的外部分数，应用将通过测量多个水平平面的各个位置的热耗散速率来回答此问题。因此，这些测量值也将提供局部湍流通量的分布。