| Gas turbine has a series of advanced technical features such as high efficiency,low noise,and low emissions.It has been widely used in the fields of energy,power,and aviation.Magnetic levitation bearing system has the advantages of frictionless wear,improved engine speed and lifespan,and is listed as one of the key advanced technologies of 21st-century gas turbines.To meet the need for high-performance power,the rotor system of gas turbines often operates at high speeds,high aerodynamic loads,and high eccentric loads,which can lead to inadequate bearing support,variable rotor vibration modes,insufficient blade clearance,and other disadvantages.The gas turbine magnetic levitation disc rotor is highly prone to multiple-point rub-impact during operation,such as rotor and protection bearing rub-impact,blade and casing rub-impact,and rotor and magnetic bearings rub-impact.This paper focuses on the research of multiple-point rub-impact vibration characteristics and fault identification methods of gas turbine magnetic levitation disc rotor system.Through methods such as structural design,dynamic modeling,finite element analysis,and numerical simulation,the friction characteristics are comprehensively discussed,providing theoretical support for effectively solving such contact problems and providing a reasonable reference for the subsequent safe and stable operation of gas turbine magnetic levitation rotors.Firstly,the structure design and modeling of gas turbine magnetic levitation rotor are carried out,including the design of radial and axial magnetic bearings.The mechanical design and size parameters of radial and axial magnetic bearings are introduced,and the structural schematic diagram and calculation parameters of radial and axial magnetic bearings are given.Finally,axial magnetic bearing simulation is carried out,and the finite element simulation verifies that the bearing magnetic bearing meets the working conditions.The above model and calculated magnetic bearing parameters provide a model foundation for subsequent analysis and optimization design of multiple-point rub-impact of gas turbine magnetic levitation rotor system.Secondly,based on the designed gas turbine magnetic levitation rotor,the rubbing dynamics model of gas turbine magnetic levitation flexible rotor is established.The mathematical expressions that induce multiple-point rub-impact are derived,involving key parameters such as eccentric excitation,aerodynamic force,and magnetic levitation bearing position.It is verified that the rigid rotor also meets this expression.The friction law of the gas turbine rotor with multiple rubbing points is revealed.As the speed increases,the rub-impact of a single point can cause rub-impact at other points.The higher the speed,the more severe the rub-impact.The optimization of multiple-point rub-impact is discussed,and optimizing the magnetic bearing PID control parameters and structural parameters can reduce the occurrence of multiple-point rub-impact faults in the rotor.Thirdly,the multi-point rub-impact characteristics of the magnetic levitation rotor considering the effect of magnetic saturation were analyzed.Electromagnetic force under magnetic saturation was calculated using finite element simulation.The results showed that the displacement amplitude of each point on the rotor changed linearly with eccentricity in the absence of contact when the magnetic field was not saturated.After magnetic saturation,the linear degree of displacement amplitude of each point on the rotor decreased,and the non-linear degree gradually increased.Magnetic saturation intensified the rub-impact of each point on the rotor.Increasing the number of turns and reducing the air gap of the magnetic bearing can prevent the occurrence of magnetic saturation,and using linear stator materials can effectively reduce magnetic saturation.Finally,a nonlinear identification method was developed for rub-impact faults in a flexible blade rotor system.A theoretical model of a variable thickness blade-disk rotor contact dynamics was established by selecting a single blade rotor.Nonlinear characteristic quantities such as average period and embedding dimension were calculated based on blade vibration response.The average period can be used to determine the occurrence of faults,and the embedding dimension and time delay can be used to identify serious rub-impact.The maximum Lyapunov exponent changes from negative to positive as the rub-impact develops,indicating the occurrence of blade rub-impact faults.Experimental testing and analysis of blade rub-impact faults in a flexible rotor system showed that the traditional time-domain and frequency-domain analysis methods have limitations,while the two nonlinear characteristic quantities proposed in this paper,namely the average period and the maximum Lyapunov exponent,can be used to identify blade rub-impact. |
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