Study On Vibration Characteristics Of Low Pressure Rotors Of Geared Turbofan Engine

As an important research direction in future commercial aviation engine area,the low pressure rotor and the fan rotor are designed under an optimum speed in order to future.improve the fuel economy and reduce the pollution emissions.Geared turbofan engine developed by P&W is typical.Because of star gear transmission system,fan rotor rotation speed can be decreased and the speed of low pressure-compressor turbine rotor can be raised.And the dynamic characteristics of the rotors are greatly different from rotor system of traditional aero engine.The low pressure rotors usually work under high speed which is above the critical speed.Its dynamic characteristic is more complex.Therefore,it’s urgent and necessary to master the dynamic characteristics and law of the coupling vibration of the low pressure rotor with star gear transmission system.The main contribution of this paper is summarized as followed:Firstly,according to the structural similarity of the complex rotating power equipment and the design principle of equal-proportion scale,the scale model of:GTF low pressure rotor system is:obtained.The finite element model of the rotor system is established based on MATLAB and SAMCEF Field respectively.The inherent characteristics of the rotor system calculated by two methods.are compared,and the results are verified by the rotor test.Then,the influence of meshigear on the natural characteristics and dynamic response of the low pressure rotor system are analyzed.Based on the precise integration method,the influence of mesh stiffness on rotor vibration is further studied by the numerical analysis model taking the time-varying excitation of the meshing gear into consideration.Besides,the vibration characteristics of the supports of gearbox and coupled pattern of rotor vibration under different working conditions of imbalance are.studied.And the influence of unbalanced excitation on gear meshing force is further studied,Finally,to verify the simulation results,the unbalance vibration test has been carried out.The results show that if the.fan rotor and the low pressure compressor-turbine rotor are calculated searately,there will be partial modal loss in fesults and the calculation of the critical speed are not reliable.And some information of unbalance response of low pressure rotors will be missing.What’s more,the gear meshing stiffness has a great effect on vibration of rotors in high speed,which is mainly shown in the dynamic response of supports of fan rotor and low pressure compressor shaft.When the rotor has imbalance,the response amplitude of low pressure rotors and gear meshing force are sometimes reduced because of the coupling effect of imbalances.When two disks of low pressure compressor-turbine rotor are unbalanced,the meshing force between the ring gear and stargear which is easier affected by the initial phase of imbalances is greater than that between the center gear and star gear.And when the phase difference is 180-deg,the imbalances will be more harmful to the rotor system.In addition,because fan rotor is at low-speed and bearing stiffness of gear rotors is large,the vibration caused by imbalance of law pressure-compressor turbine rotor can’t be balanced completely with rotating counterweights attached to the fan.