Modeling strategy and dynamic analysis of a dual-rotor-bearing-casing system in aero-engine

Abstract

In this study, a novel modeling method for a dual-rotor-bearing-casing system is proposed based on the finite element method (FEM) and the model reduction method. The dual-rotor system is modeled using Timoshenko beam and rigid disc elements, while the casing is modeled using shell elements. To reduce the number of degrees of freedom (DOFs), the modified Craig–Bampton method is used to downscale the finite element model of the casing. In addition, the Hertzian contact force and the DOFs of the bearing outer race and pedestal are considered in the bearing model. Through a specific assembly method, a dynamic model of the dual-rotor-bearing-casing is established at the expense of slight increase in the number of DOFs. Based on this dynamic model with fewer DOFs, the effects of two disc imbalances and the rub-impact fault between the low-pressure (LP) turbine and casing are then introduced as an application of the proposed model. The calculation results indicate that the critical speeds of each order of the whole aero-engine model are significantly lower than those of the casing-free model. In the amplitude-frequency diagram, the peak of the critical speed of the whole aero-engine model is found to appear earlier, and the extent of rightward bending is larger. The study also includes parametric analysis to examine the effects of parameters such as the coefficient of friction, the casing-disc contact stiffness, and the casing-foundation connection stiffness. After introducing the nonlinear bearing model, a large number of fractional frequency components are found in the frequency-domain diagram, the dynamic characteristics of the model become more complicated. The coupled bending-torsional effect has also been studied in detail, the calculation results show that it is reasonable to ignore the torsional deformation.