Post-Resonance Backward Whirl in Transient Running of Intact and Cracked Rotor Systems

Abstract

Propagation of fatigue cracks or bearing-induced damages in rotor systems that are usually exposed to recurrent transition through their resonance rotational whirl speeds during startup and coast down operations could excite the so-called post-resonance backward whirl (Po-BW) phenomena. This Po-BW is immediately captured after the passage through resonance rotational whirl speeds. Therefore, damage-induced Po-BW can be further investigated as a sign of premature failure in rotor systems. In a most recent study, this phenomenon has been numerically and experimentally confirmed to occur in cracked rotors with open-crack model. According to the literature, the aforementioned phenomenon of Po-BW is still not addressed in rotor systems associated with fatigue-based breathing crack models. Therefore, one of the latest breathing crack mechanism is employed here with Jeffcott rotor and finite element models of the considered rotor systems to perform thorough investigations to this new Po-BW phenomena. Accordingly, the Linear-Time-Variant (LTV) equations of motion are established in which startup acceleration is incorporated at different bearings and shaft conditions. Moreover, the Po-BW is also investigated in the considered cracked rotor systems with open-crack model for comparison with the breathing crack model. The same is also established to intact-rotor systems in order to verify the anticipated absence on Po-BW when isotropic bearings are incorporated. Therefore, extensive numerical simulations followed by some level of experimental validation shall be utilized to study the Po-BW in the considered cracked rotor systems. Subsequently, the Po-BW can be rendered as a unique signature for detecting propagating fatigue cracks and bearing damages in rotor systems. Consequently, this could help in leveraging damage detection techniques in presumed defected rotor systems. Experimentally, a rotor dynamical lab simulator has been employed and equipped with proximity probes to track backward whirl orbits to confirm the existence of Po-BW after the passage through the resonance rotational whirl speed. The obtained results are expected to advance the current state-of-art in the field and positively impact the long term research work in the area of rotor damage detection.

Date of Award	May 2021
Original language	American English