Application of whole engine finite element models in aero-engine rotordynamic simulation analysis

The thrust-to-weight ratio of aero-engine is increasing, the structure stiffness is reducing along with its weight, the mechanical exciting force and aerodynamic force become more and more intricate, for these reasons, dynamic interaction of different structures have to be taken into account in aero-engine vibration analysis. In traditional methods, as transfer matrix method and finite element method based on beam element, the rotor is reduced as mass point and beams, so the true dynamic interaction between the disk and shaft can't be calculated. In this paper, MSC/NASTRAN was developed by adding the effect of gyroscopic moment to the 8 nodes solid element CHEXA with DMAP (direct matrix abstraction program) language. A rotordynamic analysis of a whole engine model based on three-dimensional (3-D) solid element was performed using the program. Firstly, an unbalance response calculation of the casing was performed to predict the translation function (dynamic stiffness) at the bearing support, as well as their effects on rotor dynamics. In the analysis of solid element models and beam element models, the effects of the coupled disks and shafts vibration as well as the corner stiffness between shafts and disks on rotor dynamics were compared, the results shown that various vibration modes could be accurately calculated using the model based on solid element. A phenomenon of the coupled rotor bending and casing vibration was captured, it was shown the third rotor critical speed of the coupled rotor bending and casing vibration mode was a frequency range. The method to predict critical speeds and mode shapes of the rotor considering dynamic interaction between the rotor and casing was investigated. Finally, a simulation platform for aero-engine dynamic analysis was set up, on which the whole engine model could be found and thermal load or aero force could be considered for different purposes. It was concluded that the true dynamic interaction between the rotor and casing as well as the disk and shaft could be captured using the whole engine model based on solid element. Further more, the foreground of the thermal and tip clearance analysis of turbine blades based on the whole engine model was discussed.