Dynamic Characteristic Research Of Dual Rotor-rolling Bearing Systems

The dual-rotor structure which includes the high pressure rotor(HP rotor)and low pressure rotor(LP rotor)is often used in modern aero-engine and gas turbine rotor systems.The dual-rotor engine has better performance than a single-rotor engine.The study of the dynamic characteristics of the dual rotor system can provide a reference for the dynamic design of the dual rotor system of the gas turbine and the aero-engine,and provide the basis for the condition monitoring and fault diagnosis based on the vibration signal.The study of the dynamic characteristics of the dual-rotor system is of great engineering significance.In this paper,for the dual rotor-rolling bearing system,the following four aspects are carried out.Firstly,the dynamic model of the dual-rotor test rig is established.Using the dual-rotor test rig as the object,the dynamical model is obtained by finite element method.The rolling bearing is simplifies as the linear spring and the damper.The elastic shaft is modeled by Rayleigh beam formulation,and the disk is considered as rigid body.The moment of inertia of the shaft and the disk is taken into account in the model.Secondly,the critical speed characteristics of the dual rotor system are analyzed.Three methods of solving the critical speed of double rotor are summarized.They are the formula method,Campell graph method,speed map method.The critical speed and mode of the dual rotor model are obtained.The influence of system parameters such as bearing stiffness,speed ratio and disk inertia on the critical speed characteristics is discussed.Thirdly,the unbalanced and fixed-point rubbing response of the dual rotor system is studied by simulation,and the unbalance response is studied experimentally.For the unbalanced response,the steady-state solutions and amplitude frequency response curves without damping are obtained theoretically by superposition method,and use two kinds of numerical method for solving stiff equations which are BDF/NDF method and Newmark method to obtain the dynamic response with damping.The influence of damping on amplitude frequency response curve is discussed.The theoretical results are consistent with the numerical results.For the rubbing response,numerical simulation results indicate that the rubbing can cause the following phenomenon.The rubbing makes time-domain waveform clipping.There are multiple frequencies and combined frequencies in the spectrum.There is deformation in the axial trajectory.The experimental study is carried out on the dual-rotor test rig.The experimental result shows that the spectrum of the unbalanced response is composed of HP rotor and LP rotor rotation frequency,and the beat vibration occurs when the speed ratio is low.The experimental results are in agreement with the simulation results,and the validity of the dual-rotor model is verified.Finally,the influence of the nonlinear characteristics of the inner-shaft bearing on the dual rotor response is studied.The mathematical model of the inner-shaft bearing is established.The contact stiffness between the rolling element and the inner/outer ring is obtained.And the characteristic frequency(VC frequency,ie,Variable Compliance frequency)of the inner-shaft bearing is obtained.Combining the nonlinear inner-shaft bearing model with the dual-rotor model,the nonlinear dynamic equation of the dual rotor-rolling bearing system is established.The equilibrium response,unbalanced response and rub-impact response of the double-rotor system are studied.