Research On 3-D Finite Element Modeling And Analysis Methods Of Rotor Casing System In Mixed Coordinate System

The development of aero-engines requires higher thrust-to-weight ratio,economy and reliability.With the adoption of advanced structural parts such as blisks and large fan blades with complex shapes,the non-axisymmetry of the rotor becomes prominent.Meanwhile,the asymmetric structure and constraints of casing,coupled with the lightweight structure design inevitably lead to time-varying characteristics,and the coupling vibration problem of rotor-casing is highlighted.Based on the 3-D finite element method,the rotor-casing system model with detailed structure can be established.However,it is very difficult to build 3-D finite model or analyze the dynamic characteristics of the rotor-casing time-varying system including non-axisymmetric factors such as blades by existing methods.In this paper,a3-D finite element modeling and analysis method based on rotating-fixed mixed coordinate system is proposed.The modeling principle,modal and steady response characteristics analysis,model reduction method and practical engineering application are studied in depth,including:(1)The 3-D finite element modeling method by traditional single fixed or rotating coordinate system and application scope are analyzed and compared.Taking a axisymmetric rotor support system as the research object,the vibration characteristics characterization and mutual conversion of radial vibration of the rotor and the axial node-diameter vibration of the disc in different coordinate systems are studied.Aiming at the traveling wave resonance of the disk,the internal relations and differences of the response of rotor system in different coordinate systems are analyzed and verified by the traveling wave resonance excitation test,which lays a foundation for the proposal of modeling method based on mixed coordinate system and the expression and interpretation of solution results.(2)A 3-D finite element modeling method based on rotating-fixed mixed coordinate system is proposed.From the perspective of energy,the modeling advantages of rotating and fixed coordinate system are fully utilized.Through the equivalent mechanical parameters and energy transfer of bearing,the dynamic equation of the time-varying system of rotor support in mixed coordinate system is derived by Lagrange equation,and time-varying characteristics are expressed explictly.Based on existing solutions of periodic time-varying systems such as Hill determinant and harmonic balance method,the modal steady response analysis methods of rotor support system in mixed coordinate system are studied,and modal characteristics,order steady unbalance and gravity response characteristics of typical asymmetric rotor support system are analyzed.(3)The model reduction method based on substructure modal synthesis in mixed coordinate system is studied.The generalized fixed interface modal synthesis method is applied in mixed coordinate system model to solve the problem of casing model reduction.The simplified rotor support system is used to analyze the coupling vibration problem caused by lightweight design of casing,and the special coupling vibration form of the system under certain condition is obtained.The coupling vibration characteristics of the system are explored by a typical aero-engine high-pressure rotor intermediate casing support system.The contribution of this paper provides methods for the detailed finite element modeling of aero-engine and the analysis of coupling vibration of bladed-disk rotor-casing system.