Thermal convection on rough surfaces

粗糙表面上的热对流是一种较为通用的模型，它更适合于描述电介质中的物理过程。G.与其他基于光滑表面的模型相比，该模型更适合用于传热、电子电路冷却或研究城市地区与大气之间的热交换的设备。尽管在这一领域存在大量的出版物，但特别是，在具有粗糙度的加热或冷却壁附近的局部输运还没有得到很好的理解。这是由于这样一个事实，即只有很少的对流实验存在，这使得本地测量的运输量具有足够高的空间和时间分辨率附近的墙壁和直接的数值模拟建模的高瑞利数的建议的实验实际上需要一个过度的努力。在本研究计划中，将在大型对流实验“伊尔梅瑙桶”中测量加热/冷却粗糙表面附近的局部速度场和温度场。由于测试部分的大尺寸，直径达到7.1 m，高度达到8.0 m，这样的测量可以在高达Ra = 10^{12}的瑞利数下进行。另一方面，测量的空间分辨率仍然足够高，能够以良好的确定性验证近壁流体层中的输送量的所需函数关系。在该项目的过程中，各种表面结构，包括统一的元素和这样的交错的高度将进行调查。在他们的调查结果中，科学家们将评估各种流动现象的相关性，如热羽流速率的增加，粗糙元素顶部热边界层的“变薄”，或热边界层向湍流状态的过渡，对过去已经观察到的对流热传输的变化。此外，在各种表面结构的测量数据将进行比较和共同的特点，就其对当地的流场和热传输的影响将found. In理想的情况下，这种搜索导致一个物理模型，可能适用于类似的普遍，如在管或剪切流的水力粗糙度模型。

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.