Gravity Impact on Post-Resonance Backward Whirl Excitation by the Nonsynchronous Whirl

Rotordynamical systems are usually exposed to recurrent transition through their resonance rotational speeds during runup and coast-down operations. As a result, a nonsynchronous whirl between the shaft rotation and its lateral whirling occurs at the neighborhood of the critical resonance speeds. This nonsynchronous whirl has a significant impact on the system when a breathing crack starts to propagate. The horizontal Jeffcott rotor model with a breathing crack is considered here to study the combined effect of the gravity force vector and the nonsynchronous whirl on post-resonance backward whirl (Po-BW) excitation. The numerical simulation results show that the gravity further intensifies the excitation of the Po-BW in the horizontal cracked rotor compared with the vertical one at relatively small crack depths. In addition, the unbalance force vector orientation has been found to significantly affect the Po-BW excitation and its recurrence.