Thermal convection on rough surfaces

粗糙表面上的热对流

• 批准号: 495678007
• 负责人: Professor Dr.-Ing. Claus Wagner
• 金额: --
• 依托单位: Institut für Thermo- und Fluiddynamik
• 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/495678007?language=en
• 关键词: Thermal; convection; rough; surfaces

Thermal convection on a rough surface is a general model that is better suited to describe the physical processes in e. g. devices for heat transfer, at the cooling of electronic circuits or studying the heat exchange between an urban area and the atmosphere than other models based on smooth surfaces. Even though, a multitude of publications exists on this field, in particular, the local transport in the close vicinity of a heated or cooled wall with roughness is not well understood. This is due to the fact that only very few convection experiments exist, which permit local measurements of the transport quantities with a sufficiently high spatial and temporal resolution near the wall and that direct numerical simulations modelling the high Rayleigh numbers of the proposed experiments actually require an excessive effort. In the present research project, the local velocity and temperature fields near a heated/cooled surface with roughness will be measured in the large-scale convection experiment "Barrel of Ilmenau". Due to the large dimensions of the test section, the diameter amounts to 7.1 m, the height amounts to 8.0 m, such measurements can be done up to a Rayleigh number as high as Ra = 10^{12}. On the other hand, the spatial resolution of the measurements is still sufficiently high, to be capable to validate the wanted functional relations of the transport quantities in the near-wall fluid layer with a good certainty. In the course of the project, various surface structures including uniform elements and such ones staggered in height will be investigated. In the result of their investigations, the scientists will evaluate the relevance of various flow phenomena, like the increase of the rate of thermal plumes, the “thinning” of the thermal boundary layer on top of the roughness elements, or the transition of the thermal boundary layer towards a turbulent state, on the variation of the convective heat transport already observed in the past. Moreover, measurement data at the various surface structures will be compared and common features with respect to their effect on the local flow field and the heat transport will be found. In the ideal case, this search leads to a physical model that might be applicable similarly universally, like the model of hydraulic roughness at pipe or shear flows.

与其他基于光滑表面的模型相比，粗糙表面上的热对流是一种更适合于描述设备中的物理过程的通用模型，例如在电子线路冷却或研究城市区域与大气之间的热交换时。尽管这一领域的研究成果很多，但对粗糙壁面附近的局部输运还不是很清楚。这是因为只有很少的对流实验，这使得可以在壁面附近以足够高的空间和时间分辨率对传输量进行局部测量，并且对拟议实验的高瑞利数进行直接数值模拟实际上需要付出过多的努力。在本研究项目中，将在大型对流实验“Barrel of Ilmenau”中测量具有粗糙度的加热/冷却表面附近的局部速度场和温度场。由于试验段尺寸较大，直径达7.1m，高度达8.0m，瑞利数可高达Ra=10^{12}。另一方面，测量的空间分辨率仍然足够高，能够很好地确定近壁流体层中输运量的函数关系。在项目过程中，将研究各种表面结构，包括均匀单元和高度交错的这种结构。在他们的研究结果中，科学家们将评估各种流动现象的相关性，如热羽流速度的增加，粗糙元素顶部的热边界层变薄，或热边界层向湍流状态的转变，这些现象与过去观察到的对流热传输的变化有关。此外，还将比较不同表面结构的测量数据，找出它们对局部流场和热传输的影响的共同特征。在理想情况下，这种搜索会产生一种可能同样普遍适用的物理模型，如管流或剪切流的水力粗糙度模型。