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透平机械的稳定运行范围内，都会出现旋转不稳定性。它们对叶片的振动和噪音产生负责，因此必须避免。阻力主要出现在叶尖间隙比大或叶片发生率高的情况下。RI的旋转流动结构在时间和空间上都是起伏的。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)是产生阻力的原因。如果流体层彼此相对移动，并且由于小扰动而变得不稳定，则会出现这些SSI。该项目的目的是提高对轴流压缩机中阻力的基本机理和特性的物理理解。在大型轴流压气机的无叶流道、非旋转直线压气机叶栅和转子叶片排中，将通过实验和CFD模拟从根本上探讨SSI作为阻力触发器的假设。流动不稳定性将以不同的参数变化(如尖端间隙宽度和入射)以有针对性的方式触发。在此基础上，利用Co型和ă喷嘴，将产生一个不稳定的剪切层，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建立基本机理和阻力特性的模型概念，以及从简化的实验装置到旋转机械的可转换性。将确定出现哪些参数组合SSI，以及它们是否对RI负责。这将是制定通用规则的第一步，目的是预测和避免RI，从而有助于提高透平机械运行的可靠性。

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.