Rotordynamic Analysis Method of Small Turbo-Fan Engine Based on Finite Element Models

Small size, light weight and high speed are remarkable characteristics of modern small aero-engines. The rotor components of engine are always series connected by spline joints or face tooth joints, so dynamic interaction of different rotor components have to be taken into account in aero-engine vibration analysis. Firstly, a modal analysis of the integral series connected rotor is performed as well as the analysis of each rotor components including fan rotor, compressor rotor and turbo rotor. The result captures the effects of the rotor components on the integral rotor, the modes of the integral rotor are composed of the modes of the rotor components and the coupled modes of them. Secondly, one special characteristic of this rotor is that No.3, 4, and 5 compressor disks and compressor shaft is interference connected initially. Based on calculation of connecting state, two models of the compressor rotor are presented, including a model with connecting state effects and a general model without connecting state effects, and a rotordynamic analysis is performed with the two models. The effect of the connecting state between shaft and disks of compressor rotor on rotordynamics is captured, as well as the true critical speeds and vibration modes. Thirdly, due to different assembly state and variable mechanical force, typical parameters which affect rotordynamics directly, such as rotor support stiffness and joints structure stiffness are not constant. A sensitivity analysis of critical speeds and vibration modes with respect to typical parameters (joints structure stiffness) is performed with finite difference method, two approaches are carried out, including relative sensitivity analysis and absolute sensitivity analysis. The effect of the parameters on rotordynamics is captured, as well as the variation range of critical speed. Finally, the analysis of test data validates the author’s method.