Experimental detection of dominant sound generation mechanisms of centrifugal compressors

The main goal of this work Is the detection of the aerodynamic sound generation mechanisms of centrifugal compressors by detailed experiments and the comparison of the sound emission of four compressor variations with different aerodynamic characteristics. Furthermore, the measured data shall be used to verify the practicality of several sound prediction methods applied to highly loaded transonic centrifugal compressors. Based on these results, technical modifications for the noise sources of these compressors should be recommended. The acoustic measurements were taken for two types of impellers, each combined with either a vaneless or a vaned diffuser. The mechanisms of sound generation and propagation are investigated by analysing the spacial structure of the sound field in the inlet flow duct of the compressor and the pressure fluctuations on the inside of the impeller casing. Finally, various possibilities for designing the compressor inlet are introduced to reduce the emission at the blade tone noise.