Investigation of turbulent boundary layers with pressure gradient at high Reynolds numbers with high resolution multi camera techniques

在本研究项目中，将研究正流向压力梯度和开始分离对大尺度湍流结构的影响。此外，还将对边界层外部大尺度湍流超结构与小的近壁相干湍流结构之间的相互作用进行实验研究。还将分析大尺度结构和不同压力梯度对局地逆流事件的影响。如果局部逆流事件与大型全球流动分离的出现之间存在联系，这是本项目将研究的另一个研究问题。因为为了回答这个问题，必须解决的尺度范围很大，所以需要一种测量技术概念，允许同时分辨靠近壁面的小尺度和延伸到几个边界层厚度上的大尺度上层建筑。由于完成这项任务需要大量的设备和知识，这项分析需要德国联邦大学和德国民主力量Göttingen的合作。科学问题的答案将加强对不同湍流尺度之间相互作用的物理理解。此外，先进的时间分辨3D-PTV技术将被用来在大流体体积中获得湍流边界层和大尺度结构及其周围流动的三维图像。尽管过去在低雷诺数下进行了许多研究，但与流动相关的技术条件将是人们感兴趣的。由于这只能在具有长测试段的风洞中进行，因此实验将在位于德国明晨大学的大气风洞的22米长的测试段中进行。

In this research project, the influence of a positive streamwise pressure gradient and a beginning separation on large scale turbulent structures will be investigated. Further, the interaction between the large scale turbulent superstructures in a boundary layer's outer part and the small near-wall coherent turbulent structures will be investigated experimentally. The impact of large scale structures and different pressure gradients on local reverse flow events will be analysed as well. If there is a connection between local reverse flow events and the appearance of large, global flow separations is another research question that will be investigated within this project. Because of the large range of scales which must be resolved in order to answer this questions, a measurement technique concept is required which allows for the simultaneous resolution of the small scales near the wall and the large scale superstructures that elongate over several boundary layer thicknesses. Since a considerable amount of equipment and knowledge is required to accomplish this task, the analysis demands a cooperation between the Universität der Bundeswehr München and the DLR Göttingen. The answer to the scientific question will enhance the physical understanding of the interaction between the different turbulent scales. In addition, advanced time resolved 3D-PTV techniques will be utilized in large fluid volumina to get a 3D picture of a turbulent boundary layer and large scale structures including their surrounding flow.While many investigations have been performed at low Reynolds numbers in the past, the technical relevant flow conditions will be of interest. Since this is only possible in wind tunnels with long test sections, the experiments will be performed in the 22 meter long test section of the atmospheric wind tunnel at the Universität der Bundeswehr München.