Research Of Vibration Characteristics And Energy Tracks Of Nonlinear Dual-rotor Systems With Misalignment

A dual-rotor system is a key component of large-scale rotating equipment such as aero-engines,and must meet safe operation under extreme conditions of high temperatures,high stress,and high speeds.The vibration problems are inevitable and urgently need to be solved.The parallel dual-rotor is a common structure of modern aero-engines.Under the influence of long-term complex alternate loads,it is easy to cause unbalance and misalignment problems.Clarifying dynamics characteristics of the nonlinear dual-rotor system with misalignment have important theoretical value and engineering significance for the structural design,fault diagnoses and maintenance of aero-engines.Based on structural characteristics of the dual-rotor system with misalignment and considering nonlinear spring characteristics of the system,the dissertation proposes a new dynamics model of the nonlinear dual-rotor system with misalignment.In the dissertation,the vibration energy space analysis method is applied to nonlinear vibration analyses of the system for the first time,and influences of the misalignment fault on the vibration of the nonlinear dual-rotor system are analyzed quantitatively.Using the lumped-mass method,this dissertation constructs the traditional single-rotor dynamic equation.On this premise,combined with the characteristics of nonlinear spring restoring force,the functional formula of the nonlinear term of the four-degree-of-freedom(4DOF)single-rotor system is specifically derived.Aiming at problems of misalignment between high-and low-pressure rotors,a dynamics model of the high-pressure rotor with misalignment was established.Lagrange equations are used to derive the dynamics model of the nonlinear dual-rotor system with misalignment.The calculation of the Campbell diagram of the low-pressure rotor shows that the coupling effect of the high-pressure rotor and the low-pressure rotor leads to the coupled critical speed of the low-pressure rotor.Based on numerical simulations and frequency component analyses under linear conditions,the misalignment fault of the high-pressure rotor causes the low-pressure rotor to appear four super-harmonic resonance responses,and frequency components are dominated by 2ω components.Based on nonlinear dynamics equations of dual-rotor system with misalignment,the dissertation uses the harmonic balance method to obtain approximate theoretical solutions of the system,and combines the Routh-Hurwitz criterion(R-H criterion)to determine stabilities.The approximate theoretical solution of the system is consistent with the numerical simulation results,which proves the correctness of the model.At the same time,the vibration characteristics of nonlinear systems at different rotational speeds are studied in this dissertation.The results show that the effects of misalignment faults and nonlinear elastic restoring forces make the system appear complex nonlinear vibration states,such as flapping vibration and hybrid vibration.Using the vibration energy space analysis method,super-harmonic resonance phenomena of the low-pressure rotor of the dual-rotor system with misalignment are deeply studied in the dissertation.The variation processes between harmonic vibrations,almost periodic motions and chaotic vibrations of the low-pressure rotor are well demonstrated by using energy tracks and energy-Poincaré maps.Based on energy supply functions,vibration pattern changes of the system under misalignment faults are analyzed quantitatively.Compared with the phase space analysis theory,the dissertation creatively analyzes nonlinear vibration characteristics of the dual-rotor system with misalignment from energy points of view,which overcomes the difficult problem of multi-variable interaction decoupling.In the dissertation,a rotor experiment platform with misalignment is built,and experimental results such as vibration response curves,time histories,spectrograms and energy tracks are obtained to verify the correctness of research methods and conclusions.The results of the dissertation can provide new research directions and methods for analyzing nonlinear vibration characteristics of dual-rotor systems with misalignment.