| More electric aero-engine is an important development direction of aero-engines,and one of its key technologies is the magnetic suspended dual-rotor technology.The active magnetic bearings(AMBs)are important components of the magnetic suspended dual-rotor system(MSDS).The AMB support characteristics are not only related to the size and structural parameters,but also related to the control system and the vibration states of the rotor.On the one hand,due to the direct coupling between the AMB and MSDS,the dynamic response of the rotor will affect the AMB support characteristics through the mechanical system and the control system,which will cause the system dynamic response to change.On the other hand,there is a strong dynamic coupling between the inner and outer rotors in the dual-rotor system due to the introduction of inter-shaft bearings.These coupling effects will make the dynamic response of the system more complicated,and the establishment of the system dynamic model and the description of the dynamic behaviors are more difficult.Therefore,it is necessary to establish the MSDS dynamic model in good accordance with the AMB support characteristics,and systematically investigate the MSDS dynamic characteristics including inherent dynamic characteristics,unbalance response characteristics under normal operating conditions,and vibration characteristics under complex operating conditions such as rub-impact.These researches are of great engineering significance and theoretical value for the application of MSDS in the more electric aero-engine.Taking the dual-rotor system supported by AMBs as the research object,the dynamic theoretical model,damped critical speed(DCS)characteristics,unbalance response characteristics and rotor-stator rub-impact characteristics of the MSDS are systematically studied,and the main research contents and research results are as follows:(1)Aiming at the difficulty of modeling a dual-rotor system with two or more inter-shaft bearings using the traditional transfer matrix method,a coupled element model suitable for dual-rotor system with many inter-shaft bearings is proposed.Simultaneously,the Riccati transfer matrix method using complex variables is developed to establish the MSDS dynamic model and unbalance response model,which fully consider the AMB damping characteristics.This provides an effective method for modeling and analysis of the complex MSDS.(2)Based on the dynamic model,the disappearance process of the MSDS rigid DCSs is revealed from the perspective of complex frequency.The results show that with the increase of the AMB equivalent damping,the DCSs corresponding to the rigid modes decrease to zero and their corresponding stability margins increase significantly.The AMB equivalent damping does not change the MSDS vibration mode characteristics.Finally,some results are verified by analyzing the accelerated transient response of the MSDS.(3)Based on the unbalance response model,the influence of the MSDS parameters on the unbalanced response is analyzed,and it is found that the MSDS can safely cross the first three critical speeds by selecting reasonable control parameters.The simulation results indicate that it is more important to reduce the imbalance of the inner rotor than that of the outer rotor.In term of the MSDS stable operation from the perspectives of the AMB maximum bearing force and the maximum displacement of the AMB rotor,the latter is more difficult to achieve than the former.(4)The AMB is simplified as the model of equivalent stiffness and equivalent damping.The Lankarani-Nikravesh model and the Coulomb model are respectively applied to describe the impact force and friction force during the contact process.On these basis,the finite element method is employed to build the MSDS dynamic model with fixed-point rub-impact,and the system dynamic response is solved by Newmark-? method.(5)The vibration characteristics and the contact process are studied based on the dynamic model of the MSDS with fixed-point rub-impact,and it is found that the spectral characteristics of the MSDS can be expressed as the form of the rotational frequency difference between the inner and outer rotor,which can reflect the strong coupling effect of the inter-shaft bearing more intuitively.When the degree of rubbing is light,the integer multiple frequency components of rotational frequency difference are observed,and the rotors are in the state of forward whirl.When the degree of rubbing is intensified,the fractional multiple frequency components of rotational frequency difference appear,and the rotors are in the state of backward whirl.When the equivalent damping provided by the AMB is small and the system is running below the first order DCS,the combined frequency components of the integer multiple rotational frequency difference and the first order DCS of the system can be observed.Moreover,the maximum contact depth and impact force during the rub-impact process depend on the initial impact speed.It is also found that reasonable selection of AMB control parameters can significantly reduce the severity of the rub-impact,and even avoid the rub-impact when the MSDS operates at the rigid DCSs. |
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