Abstract
This paper establishes a dynamic model of Geared turbofan (GTF) star gear-rotor coupling system, in which the flexibility of shaft, disk, shell, diaphragm coupling, ring gear, and carrier are all taken into consideration. Additionally, an internal meshing model for flexible ring gear is developed, and the matrix reduction techniques is introduced to enhance the computational efficiency. Based on the dynamic model, the modal characteristics of the coupling system are extracted, and the influence of structural flexibility are investigated. Considering gyroscopic effect of the rotor, the Campbell diagram and the critical speeds are obtained. In addition, the vibration amplitudes under unbalanced excitation and time-varying mesh stiffness (TVMS) excitation are calculated and compared. The results of modal characteristics analysis indicate that many of the star gear train models are greatly affected by structural flexibility. Besides, the counter-rotating between the low-pressure rotor and the fan rotor results in frequency veering in the Campbell diagram, which is rarely observed in parallel gear-rotor system. The vibration responses indicate that unbalanced excitation of the rotor has relatively less effect on the gear vibration, while the low frequency excitation at star gear train is capable of exciting resonant vibration of the rotor.
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