Breakdown of tip clearance vortices in periodically unsteady flow

该项目将有助于更好地理解高负荷轴流压缩机中各种流动现象的复杂相互作用。虽然转子和定子本身的顺序已经导致上游尾流对后续叶片周围的流动的影响，但附加的固有二次流对压气机级的性能和流动稳定性有很大贡献。一个主要的影响来自于穿过型材和流动通道的轮毂壳体之间的差距的流动，由于当今型材的高负载，这变得越来越重要。结果是与主流相互作用的强涡流系统。在以前的研究项目中，在一个环形风洞的椅子上的航空发动机，它被发现，特别是这些旋涡本身的崩溃导致严重的变化，在叶栅内的流动，从而其性能方面的流动稳定性，阻塞和压力增加。该项目的目的是确定来自上游转子的周期性尾流对现有涡流系统形成的影响以及由此产生的流型。风洞是非常模块化的，并允许集成转子具有不同直径的杆，并以可变的转速运行。这样就可以直接比较叶栅内的定常流和非定常流。此外，可以评估进入的尾流是否以及如何导致加强和阻尼由穿过轮廓间隙的泄漏流引起的涡流破裂。转子构型的变化可以用来研究不同参数对叶栅性能的影响。调查将通过最先进的测量技术进行，包括立体PIV系统，热线风速计和压阻传感器。由于其强大的时间分辨能力，这些系统非常适合这种类型的流量，并在研究所建立良好。

This project shall contribute to a better understanding of the complex interaction of various flow phenomena in highly loaded axial compressors. While the sequence of rotors and stators itself already leads to an influence of the upstream wakes onto the flow around a subsequent blade, additional inherent secondary flows contribute significantly to the performance and flow stability of the compressor stages. A major impact stems from the flow across the gap between the profiles and the hub respectively casing of the flow channel, which is becoming more and more important due to the high loading of todays profiles. The results are strong systems of vortices, interacting with the main flow. In preceding research projects in an annular wind tunnel at the chair of aero engines, it was found, that especially the breakdown of these vortices in itself leads to severe changes of the flow within the cascade und thus its performance in terms of flow stability, blockage and pressure increase. The objective of the proposed project is the determination of the impact of periodical wakes coming from an upstream rotor onto the formation of the existing vortex systems and the resulting flow pattern. The wind tunnel is extremely modular and allows for the integration of a rotor featuring bars with different diameters and running at variable rotational speeds. Thus a direct comparison between the steady and the unsteady flow within the cascade becomes possible. Further on, it can be assessed, if and how the incoming wakes lead to fortification respectively damping of the breakdown of the vortices caused by the leakage flow across the profiles gaps. The variability of the rotor configuration can be used to study the effect of different parameters on the performance of the cascade. The investigations will be performed by means of state-of-the-art measurement technology, including stereo-PIV-systems, hot wire anemometry and piezoresistive sensors. Due to their strong time-resolving capabilities, these systems are highly suitable for this type of flows and are well established at the institute.