Interpretation of Stall Precursor Signatures

Abstract Unsteady aerodynamic phenomena appearing close to the stall boundary in axial fans and compressors have been subject of extensive investigations. A particular phenomenon known as “rotating instabilities” typically occurs tip region at highly loaded conditions is often linked blade vibrations. During rig engine testing, it usually identified by characteristic shape its pressure spectra. In 1990s, this has explained result a circumferentially propagating disturbance, which unsteady frame reference rotating with disturbance. analysis, conclusions regarding propagation speed frequency made based on analysis spectral peaks, method still used classify phenomena. However, high subsonic transonic machines, where aeroacoustic aeroelastic interact disturbances, interpretation measurements using spectra alone challenging. The present article aims demonstrate difficulties subtleties associated measurement signals, need be overcome correctly interpret precursor signatures. At example recent investigation composite fan, consequences sensor placement postprocessing techniques are discussed focus averaging, isolation non-synchronous phenomena, multisensor cross correlation methods. It seen that solely peaks their spacing can misleading features instability spectrum do not require an unstable pulsating