The interaction of the tip clearance vortex system of tandem blades in a high-speed linear cascade

本项目的目的是促进对串列叶片叶顶间隙涡系统的理解。在涡轮机械中，旋转元件和静止元件之间必然存在的间隙会造成重大损失。传统压气机叶片具有单叶尖间隙涡，这对流动损失和稳定性有很大影响。与此相反，串联叶片形成至少两个涡的系统，这是由于在每个单独的串联叶片上形成叶尖间隙涡造成的。本课题对串联叶片叶尖间隙区域的流场进行了详细的分析。实验研究将在高速线性压气机叶栅中进行。第一个重点是分析两个串列叶尖间隙涡与靠近侧壁流场的相互作用。旋涡分解（VBD）的现象-已知的叶尖间隙涡在传统叶片-应研究其发生在串列叶片。以前的研究已经揭示了一个操作点，最有可能的是，只有前叶尖间隙涡经历VBD。应进行安装壁面压力测量，以确认这一点，并允许更详细的了解。接下来，将分析是否可以确定一个较高发生率的工作点，在该工作点上两个叶尖间隙涡都显示VBD，以及它如何影响流场及其相关损失。在下一步，配置将被分析，其中只有串联前或后叶片显示一个尖端间隙。这样，在没有另一个涡的存在和影响的情况下，可以评估一个涡的行为。结果将显示流动现象（如VBD的个别点）是否在相互影响下向不同的发生率转移。此外，还对损失来源和损失发展进行了研究。结果将揭示某些损失是由前叶尖间隙涡、后叶尖间隙涡还是两者的相互作用造成的。实验是通过安装壁面压力测量和应用一种新型的表面栅栏探针进行的，该探针用于确定壁面剪应力。

The aim of this project is to contribute to the understanding of the tip clearance vortex system of tandem blades. The necessarily existing clearances between rotating and stationary elements in turbomachinery cause significant losses. Conventional compressor blades feature a single tip clearance vortex, which has a majorinfluence on flow losses and stability. In contrast to that, tandem blades develop a system of at least two vortices, which result due to tip clearance vortices forming on each, individual tandem blade. In this project a detailed analysis of the flow field in the tip clearance region of tandem blades is planned. Experimental investigations will be conducted in a high-speed linear compressor cascade. The first point of focus lies on theanalysis of the interaction of the two tandem tip clearance vortices with the flow field close to the side wall.The phenomenon of vortex break down (VBD) - known from tip clearance vortices on conventional blades - shall be investigated in its occurance on tandem blades. Previous investigations have revealed an operating point in which most probably, only the front tip clearance vortex experiences VBD. Instationary wall pressure measurments shall be done to confirm this and to allow for a more detailed understanding. Following, it willbe analyzed whether an operating point at higher incidences can be identified at which both tip clearance vortices are showing VBD and how this impinges on the flow field and its associated losses. In the next step, configurations will be analyzed in which only the tandem front or rear blade exhibits a tip clearance. Thus, a vortex’ behavior without the presence and influence of the other vortex can be assessed. The results willshow if flow phenomena (such as the individual point of VBD) are shifted towards different incidences by the mutual influence. Furthermore, the loss sources and loss development are investigated. The results shall reveal whether certain losses result from the front tip clearance vortex, the rear one or the interaction of the two of them. The experiments are conducted using instationary wall pressure measurements and by the application of a novel surface fence probe, which is used to determine the wall shear stresses.