Dynamic Characteristics Of Two-Span Rotor-Bearing System With Flexible Diaphragm Coupling Misalignment

The prevalence of distributed energy resource makes the development of efficient microturbines.The high-speed direct-drive rotor system is an effective structure to improve the power density of gas turbines.Because the longer length of two-span rotor system highlights the misalignment fault and changes the dynamic characteristics,it is necessary to study the dynamic stability of two-span rotor system.This paper is based on a high-speed direct-drive rotor system in the MW gas turbine generator set.Through the research on the diaphragm coupling,the dynamic characteristics of two-span rotor system and the dynamic characteristics of two-span rotor system with misalignment,the main work had done as followed.1.By establishing the whole structural model of hyperbolic diaphragm coupling,the reasons that diaphragm coupling compensate for misalignment were explained,and the influence of diaphragm coupling stiffness with the structural parameters was obtained.2.By establishing the finite element model of two-span rotor system with diaphragm coupling,the dynamic characteristics of two-span rotor system was analyzed.3.By establishing the finite element model of two-span rotor system with diaphragm coupling misalignment,the influence of misalignment and coupling stiffness on the two-span rotor system was analyzed,which can provided for theoretical support for the misalignment fault diagnosis and design of double-span rotor system.4.Considering the dynamic characteristics of two-span rotor system under complex loads,the variation law of the dynamic characteristics of two-rotor by Alford force and unbalanced magnetic pull force was studied.Through the study mentioned above,some conclusions are obtained as follows:1.Because the thickness of diaphragm structure is rather thin,it is necessary to consider the nonlinear variation of stiffness due to the large deformation of diaphragm structure.The thickness of the outer diameter,the ratio of internal and external diameters and the length of intermediate shaft are important structural parameters which affect the diaphragm coupling stiffness.2.The critical speed and mode shape of two-span rotor system are related to the single rotor system,and the increase of diaphragm coupling stiffness raises the critical speed and unbalanced response of two-span rotor system.3.The influence of misalignment on unstable speed is small,but the system show more dynamic characteristics,such as cycle 4 and 5.The increase of diaphragm coupling radial stiffness and angular stiffness enhances the unstable speed of rotor system and the amplitude of 2X component response.4.Under the action of Alford force and unbalanced magnetic pull force,the range of chaotic motion is reduced and more forms of periodic motion appear.