Blade Self-excited Vibration with Identification of Fan Using Microphone Array

The identification of blade self-excited vibration on a fan is attached to great importance for aero-engine operation safety. A non-contact method based on acoustic measurement is proposed to identify blade self-excited vibration via the run-up test, where a circular microphone array is arranged in the inlet section of a three-stage fan. The test results at 6880r/min present that the asynchronous aerodynamic excitation frequency has a connection with the asynchronous blade vibration frequency. In order to reveal the connection between sound pressure fluctuations and blade vibration in asynchronous vibration phenomena, the acoustic mode decomposition are carried out. The experimental results shows that the fan blade exists asynchronous vibration when the dominant acoustic mode order decomposed at the asynchronous aerodynamic excitation frequency is the same as the nodal diameter. A brief formula is provided to reveal the connection of sound signals to identify asynchronous vibrations.