TutorialThere are several sources of non-synchronous forced vibration of centrifugal compressor rotors. Many of them are aerodynamic phenomena, created within the gas path of the compressor. Phenomena such as impeller stall, diffuser stall (with and without vanes), and flow instabilities caused by impeller to diffuser misalignment, are all characteristic flow disturbances that can cause forced vibration. In fact, often the only indications of these phenomena are found in the resulting rotor vibration signals. Several phenomena that can cause non-synchronous vibration are reviewed, and for each one, background information, as well as detailed descriptions of the flow field, or other source of the excitation, is provided. This includes the use of CFD analytical results to describe the flow where applicable. The review also includes, when available, dynamic pressure transducer test data that can be used to verify the presence of the phenomena, and rotor vibration data indicating the presence of such phenomena. This includes test data of actual machines, indicating characteristics such as frequency and amplitude
