大型离心叶轮振动模态局部化特性研究

Study on the vibration localization in the centrifugal Impeller with periodic structures

为了研究目前工程中大型流体机械离心叶轮出现的局部疲劳破坏的机理,基于现有的有限元分析方法,结合模态分析等动力学理论以及叶轮所承受的气流激励,对其动力学特性进行了研究。着重研究了离心叶轮这类周期循环对称性结构具有的不同于非周期循环结构的特殊动力学性质以及该特殊的动力学特性与叶轮疲劳破坏的联系。研究发现其存在频率通带(passbands)、频率禁带(stopbands)现象,并出现了振动模态局部化现象。另外,叶轮的动力学特性对其周期性结构失谐特别敏感,该类失谐可来自由制造误差、材料和使用中磨损出现的不均匀等多种因素。对于协调结构,在一定条件下(如系统具有高密集模态),很小的失谐量(1%)就可使结构振动模态产生急剧变化,从而出现振动模态局部化现象。对于所研究的机组,当进口预旋器导致的流体激振频率(1166.7Hz)接近叶轮的由第12阶～18阶固有频率组成的禁带(1020.3～1054.5 Hz)时,数值分析结果显示叶片进口部位出现了振幅较大的振动,与该机组实际破坏的部位相符。研究结果表明所使用的振动模态局部化分析方法能够揭示叶轮发生疲劳破坏的原因,即是一类共振型疲劳破坏现象。

From the viewpoint of dynamics,the nature of the fatigue failure of a centrifugal impeller is presented.By using finite element method and mode analysis,the dynamics of the centrifugal impeller is studied numerically.It is found that centrifugal impeller is the typical periodic structures,and there exist many unique dynamics in comparison to non-periodic structures,such as the vibration localization,passbands and stopbands.The amplitude and the resulting energy will be uniform in the structure as the exciting force in the range of passbands.On the other hand,the amplitude and the resulting energy will be limited at local part,and the amplitude and stress will be increased greatly,the centrifugal impeller will be destroyed as the energy is localized.Additionally,influences of mistuning from the manufacture process,material and wear on the dynamics of the system are significant.For some cases,such as the structure with dense modes,small mistuning(1%)will lead to great change of the mode,result in vibration localization.For the centrifugal impeller studied,the numerical results show that the inlet portions of blades behave with large amplitude and train,as the exciting frequency(1166.7Hz)from inlet guide vane is close to the stopband(1020.3 Hz-1054.5 Hz)of centrifugal impeller,and it agrees well with the broken centrifugal impeller.As a conclusion,it can be drawn that such mode localization is the key to the fatigue failure of the centrifugal impeller and such fatigue failure results from resonance.