Interference of Unbalance on the Dynamic Characteristics of Cracked Rotor: An Experimental Research

Abstract When the rotor of an aeroengine or gas turbine contains cracks, it produces abnormal vibrations. The abnormal vibration behavior of the cracked rotor can be used as the basis for crack fault diagnosis. However, in practice, the rotor itself cannot achieve absolute dynamic balance. Also, the operating environment in which the rotor is placed may contain unbalanced excitation. During the rotation of the cracked rotor, the existence of unbalance interferes with these abnormal vibration characteristics. Therefore, studying this process is of great significance for solving the issue of rotor crack fault diagnosis under unbalanced disturbance in engineering. This study aimed to monitor the dynamic characteristics of a multi-disk rotor system with transverse cracks. An unbalanced mass was imposed at the disk. Precision wire cutting was used to prefabricate cracks on the rotor to maximize the simulation of fatigue cracks in the real industrial environment. During the test, the crack depth was from shallow to deep and the direction of the crack opening remained unchanged, while the direction of unbalanced force changed 360° along the circumferential direction of the disk. The experimental results showed that when the angle between the unbalanced force direction and the crack opening direction changed, the crack fault characteristics changed to different degrees. The effect of unbalance on crack fault characteristics was more obvious with the increase in crack depth.