Localization of rotating sound sources in the presence of duct modes

Kurzfassung

Localization of rotating sources inside ducts via microphone array methods can be limited due to dominant modes and uncorrelated noise content obscuring the signals from the sources. Especially in axial compressors, the rotating sources related to the rotor blades can be difficult to locate at frequencies with tonal peaks, that contain correlated modal content. To overcome these limitations, this contribution suggests a compound method to attenuate the dominant modes and uncorrelated noise in signal processing.Based on measurements from an axial-compressor test rig with wall-mounted microphones, improvements of the in-duct localization of rotating sound sources are demonstrated. Synchronously measured signals are initially brought into a rotating reference frame through virtual rotation. Next, tonal components of each microphone signal are separated using a time-domain cyclostationary approach. Finally, using the remaining broadband signal, the cross-spectral matrix noise content is reduced by diagonal reconstruction through energy fitting in mode-domain (DREF-M).The application of beamforming with this combined approach enables the characterization of rotating sound sources at frequencies where masking of the sources cannot be eliminated by using only one of the given methods and at frequencies with strong tonal content.