Rotating Instabilities in Axial Compressors – Investigation of the Formation Mechanism in Stationary and Rotating Blade Rows

旋转不稳定性（RI）不仅出现在轴流压缩机的稳定运行范围内，而且也出现在其它类型的压缩机中。它们是叶片振动和噪声产生的原因，因此必须避免。RI主要出现在叶尖间隙比大或叶片冲角大的情况下。RI的旋转流结构在时间和空间上是波动的。关于RI的潜在机制有几种解释方法。一种假设认为端壁附近的剪切层不稳定性（SSI）是RI的原因。如果流体层相对于彼此移动并且由于小的扰动而变得不稳定，则这些SSI可以出现。 该项目的目的是提高对轴流压气机中RI的基本机理和性质的物理理解。本文将通过实验和CFD模拟的方法对SSI作为RI触发因素的假设进行初步的研究，包括在无叶通道、非旋转压气机叶栅和大型轴流压气机动叶排中的研究。流动不稳定性将通过不同的参数变化（例如叶尖间隙宽度和冲角）以有针对性的方式触发。此外，使用Coander-nozzles，一个不稳定的剪切层将产生和旋转流结构的影响将investigated.Focus的详细的实验和数值研究的基础机制和RI的属性，以及从简化的实验装置的见解向旋转机的可转移性的模型概念的发展。将确定哪些参数组合SSI出现以及它们是否对RI负责。这将是制定一般规则的第一步，目的是预测和避免RI，从而有助于提高发动机运行的可靠性。

Rotating Instabilities (RI) can appear in the stable operating range of axial compressors as well as in other turbomachines. They are responsible for blade vibration and noise generation and have therefore to be avoided. RI mainly emerge for large tip clearance ratios or high incidence of the blading. The rotating flow structures of RI are fluctuating in time and space. There are several explanatory approaches concerning the underlying mechanism of RI. One hypothesis states that shear layer instabilities (SSI) near the endwall are the reason for RI. These SSI can appear if fluid layers move relative to each other and become unstable because of small disturbances. Aim of this project is to improve the physical understanding of the underlying mechanism and the properties of RI in axial compressors. The hypothesis of SSI as trigger of RI will be fundamentally investigated by means of experiments and CFD simulations in the vaneless channel, in the non-rotating linear compressor cascade and finally in the rotor blade row of a large scale axial compressor. The flow instabilities will be triggered in a targeted manner with different parameter variations, e.g. tip gap width and incidence. Further on, using Coandă-nozzles, an unstable shear layer will be generated and its influence on rotating flow structures will be investigated.Focus of the detailed experimental and numerical investigations are on the development of model conceptions of the underlying mechanism and the properties of RI as well as the transferability of the insights from simplified experimental setups towards the rotating machine. It will be determined for which parameter combinations SSI appear and if they are responsible for RI. This will be a first step for the development of general rules with the aim to predict and avoid RI and thus contribute to an improved reliability of operation of turbomachines.