Time–frequency features of two types of coupled rub-impact faults in rotor systems

Two types of rub-impact faults in rotor systems are studied in this paper. First is crack coupled with rub-impact, and second is oil-film instability coupled with bearing rub-impact. By combining spectrum cascade, reassigned wavelet scalogram, rotor trajectory, and frequency spectrum, some novel fault features have been discovered from the vibration signals measured in both the speeding up and slowing down process. The results show that for crack coupled with rub-impact fault, the system motion is from period-three motion, to period-two motion, then to period-four motion in the slight rub-impact stage. However, in the stage of the serious rub-impact, chaotic motion occurs. For oil-film instability coupled with rub-impact fault, rotational frequency, oil-film instability frequency, and the combined frequencies of them can be observed when slight bearing rub-impact occurs. When bearing rub-impact is increasingly serious, the increase of low frequency amplitude can be viewed as the most distinguishable characteristic.