Abstract
Support looseness fault is a type of common fault in aeroengine. Serious looseness fault would emerge under larger unbalanced force, which would cause excessive vibration and even lead to rubbing fault, so it is important to analyze and recognize looseness fault effectively. In this paper, based on certain type turbofan engine structural features, a rotor-support-casing whole model for certain type turbofan aeroengine is established. The rotor and casing systems are modeled by means of the finite element beam method; the support systems are modeled by lumped-mass model; the support looseness fault model is also introduced. The coupled system response is obtained by numerical integral method. In this paper, based on the casing acceleration signals, the impact characteristics of symmetrical stiffness and asymmetric stiffness models are analyzed, finding that the looseness fault would lead to the longitudinal asymmetrical characteristics of acceleration time domain wave and the multiple frequency characteristics, which is consistent with the real trial running vibration signals. Asymmetric stiffness looseness model is verified to be fit for aeroengine looseness fault model.
Highlights
Looseness fault is a common fault in rotating machinery, which is caused by low installation quality or long-term vibration
When looseness fault exists in rotor-support-casing system, rotor will be lifted up periodically; if the unbalanced force in rotor system is greater than the gravitational force, it will cause severe vibration
Many scholars have carried out a few works on the looseness fault, mostly based on a lumped-mass model
Summary
Looseness fault is a common fault in rotating machinery, which is caused by low installation quality or long-term vibration. Ji and Zu [7] analyzed the free and forced vibration of a nonlinear bearing system to illustrate the nonlinear effect on the free and forced vibrations of the system by the method of multiple scales He et al [8] and Lee and Choi [9] studied fault diagnosis of rotor systems with pedestal looseness with different analytical methods, such as genetic algorithm and Hilbert-Huang transform. Behzad and Asayeshthe [12] proposed a finite element method for studying the effects of loose rotating disks on the rotor-bearing systems’ response. Due to the low bearing stiffness in aeroengine, the wide use of thin-walled structure in rotor and casing, its great flexibility, and the casing acceleration signal are important to distinguish aeroengine faults, so aimed at certain type turbofan engine, it is of great significance to establish a whole model of a rotor-bearingcasing coupling system and make research on the acceleration response characteristics of the looseness fault. It is proved that the aeroengine support looseness fault model is valid
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