Mechanism and propagation of characteristic frequency noise inner a high pressure compressor

An acoustic experiment on a high pressure compressor is implemented to investigate noise mechanism and propagation corresponding to high level vibration occurred on rotor blades. The results show that, noise spectrum tested on the first stage rotor blades of high pressure compressor presents typical characteristics for discrete multi-tone in a pre-arranged structure adjustment and specific rotating speed. These discrete frequencies are composed with blade passing frequency of the first stage rotor blades and other special characteristic frequencies. And the amplitude of characteristic frequency 1402Hz will synchronously increase with the sharp vibration of the rotor blades. Rotating speed plays an important role on the characteristic frequency. This frequency merely occur on the specific speed range, and has relationship with structure adjustment of the compressor. With the rotating instability theory, the generation mechanism of the frequency can be explained with a rotating sound source having the same speed with the first stage rotor blades. The frequency of the rotating noise source will match with the characteristic frequency at a specific mode. Through the coherent analysis between the noise measured at different testing positions, this characteristic frequency noise source originates behind the first stage rotor blade at least. Therefore, the propagation state should be from back to forward with a circumferential speed. All these analysis reveal generation mechanism and propagation characteristic of the discrete frequency inner the compressor which may have an important reference value for Engineers.