Investigation of sound generation by non-synchronously vibrating rotor blades

The blade fatigue failure is a common aeroelastic problem of axial compressor. The phenomenon accompanied with blade vibration is abnormal acoustic field generation in compressor duct. The frequency of sound field generated by non-synchronously vibrating rotor blades is unequal not only to the compressor rotational frequency, but also to the blade passing frequency that is identical with sound generated by stator and rotor interaction. Meanwhile the frequency cannot be explained by typical Doppler shift phenomenon. In this paper, a theoretical model based on the three-dimensional lifting surface theory has been built to demonstrate the frequency and circumferential modal characteristics of the sound generated by rotor blades vibration. The developed model illuminates the fact that the sound frequency and circumferential mode depend a lot on the inter-blade phase angle. The experiment results verify the relationship between sound generation and blades vibration given by the model.