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

在轴流压气机和其他涡轮机械的稳定运行范围内，都会出现旋转不稳定性。他们负责叶片振动和噪音的产生，因此必须避免。主要表现为叶尖间隙比大或叶片发生率高。RI的旋转流结构在时间和空间上都是波动的。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。如果流体层彼此相对移动并且由于小的扰动而变得不稳定，则会出现这些SSI。该项目的目的是提高对轴向压缩机中RI的基本机制和特性的物理理解。通过在无叶通道、非旋转线性压气机叶栅以及大型轴流压气机动叶排的实验和CFD模拟，从根本上研究SSI作为RI触发的假设。不同的参数（如叶尖间隙宽度和入射角）会有针对性地触发流动不稳定性。在此基础上，利用协同喷嘴产生不稳定剪切层，并研究其对旋转流动结构的影响。详细的实验和数值研究的重点是对潜在机制和RI属性的模型概念的发展，以及从简化实验设置到旋转机器的见解的可转移性。将确定哪些参数组合出现SSI，以及它们是否负责RI。这将是制定通用规则的第一步，旨在预测和避免RI，从而有助于提高涡轮机器的运行可靠性。

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.