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.

大多数包含对流热传递的地球物理和工程过程的特征在于流体层的横向和垂直范围之间的大比率。然而，关于热对流的实验和数值研究仍然集中在这个比率相当小（等于或小于1）的配置上。特别地，这是由于这样的事实，即实现相当高的瑞利数的实验必须非常高，并且通常这种大的高度不能由相应的宽度补偿。因此，它实际上是不可能充分评估的唯象理论，通常是基于一个一维模型没有横向约束。申请人希望通过在同时满足高纵横比（8或更大）和高瑞利数（高达10{12}）的实验中测量热通量和散热速率来克服这一点。与前一个项目不同，他们将专注于这两个量的动态的新工作。它是由Scheel和Schumacher [J. Schumacher和J.D.谢尔湍流对流单体中烟羽碰撞引起的极端耗散事件。E 94，043104（2016）]，特别地，热耗散速率在局部以及在时间上非常强烈地波动。这将首次在实验中得到验证。因为测量可能覆盖比可比DNS长得多的“观测期”，所以测量数据的统计不确定性将显著更小。在第二部分中，申请人将追求以下问题：对于整个相应的水平面，在单个点（在湍流瑞利-贝纳德对流中）的局部和时间平均测量数据的代表性如何。对于小于或等于1的宽高比，过去一直在研究这个问题，并以“不具有代表性”来回答。对于大的纵横比，其中侧壁仅影响流体层的很小的外部部分，申请人将通过在多个水平面中的各个位置处测量热耗散率来回答这个问题。因此，这些测量也将提供局部湍流热通量的分布。