Interaction of rotating instabilities and stall in axial compressors

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The proposed project focuses on Rotating Instability (RI), which is known as a prestall instability in axial compressors. Referring to own recent experimental and numerical investigations, the physical mechanism of RI needs to be reflected on a generic model. Based on a systematical reduction of necessary boundary conditions, a Kelvin-Helmholtz-Instability is to be generated in an annulus where the disturbances propagate circumferentially. Afterwards pressure fluctuations being induced by the Kelvin-Helmholtz-Instability will be investigated using established analysis methods for the identification of RI. In order to extend the scope of parameters, the impact of periodical wakes coming from an upstream blade row onto the formation of RI will be investigated. In detail, the main objective is to analyze the influence of specific excitation frequencies on spectral, modal and time-resolved RI characteristics. In a multidisciplinary approach, a possible influence of RI through a targeted adjustment of the number of blades would also provide a great scientific benefit in the field of aeroelasticity of turbomachinery. It is known that RI can be one of the reasons for non-synchronous blade vibrations. In addition, the extremely short-timed inception process of rotating stall will be investigated under the additional influence of RI. It will be clarified whether RI is provoking the development of stall cells and which driving mechanisms are involved in this process. In this context, the interaction between RI and well-known inception mechanisms such as "spikes" or "modes" will be analyzed. The results have great potential to contribute significantly to the subject of rotating stall inception. Over the last decades the topic RI is part of lively but also controversial discussions. Even the term "Rotating Instability" was considered inappropriate by parts of the community. Thus, the proposed project supports an unambiguous classification of RI into the field of "compressor instabilities" and "stall inception".