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Modal characteristics analysis for a flexible rotor with non-smooth constraint due to intermittent rub-impact

Chinese Journal of Aeronautics 2018年第3期31卷 498-513页

作者： Jie HONG Pingchao YU Dayi ZHANG Zhichao LIANG School of Energy and Power Engineering Beihang University Collaborative Innovation Center of Advanced Aero-Engine Beihang University

Intermittent rub-impact, during which the contact between rotor and stator is characterized by a ‘‘bouncing＂ or intermittent type of behavior, is one of the most common rubbing forms in rotating machinery. When the intermittent rub-impact occurs, the non-smooth constraint, which is the phenomenon that the system stiffness changes with respect to the state of contact and noncontact, will appear. The paper aims at discovering the possible effects of the non-smooth constraint on the flexible rotor＇s Modal characteristics by theoretical and experimental methods. The qualitative description for non-smooth constraint is given for the intermittent rub-impact process, and the dynamic modeling for a rotor system with non-smooth constraint is carried out. Meanwhile, the analysis method is developed by Floquet theory and Hill＇s method to obtain the rotor＇s Modal characteristics. The results reveal that the non-smooth constraint produced by the intermittent rubimpact will increase the modal frequencies and critical speeds of the rotor system significantly.Due to the time-varying features of the constraint stiffness, the modal frequencies for the intermittent rub-impact rotor present fluctuant changes with the increase of rotation speed, which is different from the general linear rotor system. The non-smooth constraint is possible to lead the rotor＇s instability, and the rotor＇s instable regions can be expanded significantly for the increase of average constraint stiffness, constraint amplitude and contact time ratio. Non-smooth constraint could also expand the resonance speed and resonance sideband of the rotor system, which sometimes results in amplitude jump phenomenon.

关键词： Flexible rotor Intermittent rub-impact Instabifity Modal characteristics Non-smooth constraint

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modal analysis strategy and nonlinear dynamic characteristics of complicated aero-engine dual-rotor system with rub-impact

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Chinese Journal of Aeronautics 2022年第1期35卷 184-203页

作者： Pingchao YU Guo CHEN Lunxu LI College of Civil Aviation Nanjing University of Aeronautics and AstronauticsNanjing 211106China

This paper aims to gain insight into the nonlinear Modal characteristics and the possible influence of the modes on the responses for the practical dual-rotor system with rub-impact in aero-engine.The finite solid element method combined with a constraint stiffness model produced by rub-impact is introduced to build the governing equation of the complicated nonlinear dual-rotor system.In order to deal with the efficiency and numerical divergence in the process of solving the nonlinear modes of this large-scale nonlinear system,an analysis strategy is proposed by integrating a two-layer reduction technique into the harmonic balance method.The effectiveness of the analysis strategy is validated by applying to a simple rotor system,which can easily obtain the theoretical result.Based on the modeling method and analysis strategy,the Modal characteristics of an aero-engine dual-rotor system with rub-impact are revealed.The results show that the modal frequency of the dual-rotor system increases when rub-impact occurs and has the feature of interval,which allows us to obtain the critical speeds of the rubbing system by traditional Campbell diagram.The rotation direction is an important factor since it can not only affect the gyroscopic effect but also change the friction effect of the rub-impact.It is found that the modal frequencies of the counter-rotation dual-rotor are less than those of co-rotation condition.More importantly,the forward modes of the counter-rotation dual-rotor may be instable when rub-impact occurs at a certain rotor,while the corresponding modes under the co-rotation condition are always stable.Furthermore,by analyzing the rubbing response of the dual-rotor,it is found that the Modal characteristics have an important influence on rotor’s response.The instable forward modes existing in the counter-rotation dual-rotor may lead to the divergence of the response when passing the corresponding critical speed.

关键词： Dual-rotor system Instability Modal characteristics Rub-impact Vibration response

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