14th European Conference on Turbomachinery Fluid dynamics & Thermodynamics
Non-synchronous vibrations arising near the stall boundary of compressors are a recurring and potentially safety-critical problem in modern axial compressors. Recent numerical and experimental investigations have shown that the vibrations are caused by the lock-in of circumferentially convected aerodynamic disturbances and structural vibrations, and that it is possible to predict unstable vibration modes using coupled linear models. This paper aims to further investigate non-synchronous vibrations by casting the model in the frequency domain and analysing stability for a range of parameters. It is shown, how and why, under certain conditions linear models are able to capture a phenomenon, which has traditionally been associated with aerodynamic non-linearities. The formulation clearly highlights the differences between convective non-synchronous vibrations and classical flutter and identifies the modifications necessary to make quantitative predictions.