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一、前言近年来,由于国产中间再热机组在试运过程中曾多台次发生低频强烈振动,引起人们对低频振动现象的重视。造成汽轮机组低频振动的原因虽有多种;但主要的和经常发生的只有两种:一是油膜振动;另一种就是因蒸汽涡动而引起的转子自激振动,通常称为气流激振(flow excited vibrations)或称间隙激振。由于气流激振现象与油膜振动现象相似,特别是在机组带负荷阶段发生低频振动时,更容使人怀疑是由于气流激振所造成。国产20万千瓦和30万干瓦机组,投产初期也遇到过在带负荷阶段发生低频振动。按照20万千瓦机组的现场分析,曾怀疑气流激振是原因之一,但根据目前的认识,虽然认为它还不属于气流激振的现象,但对于大机组来说,气流激振确是当前值得重视的一个问题。而国内在介绍气流激振方面的文章又很少。为了弄清气流激振和油膜振动两者的差别,本文拟对气流激振的现象、机理及消除措施作一简要介绍,并对国内大机组产生气流激振的可能性提出初步看法,以期在大机组投运前,能引起对这一问题的注意。
I. Introduction In recent years, as the domestic reheat unit in the trial process during which many times a strong low-frequency vibration, causing people to pay attention to low-frequency vibration phenomenon. Although there are many causes for the low-frequency vibration of steam turbines, there are only two main and frequently occurring ones: one is oil film vibration; the other is rotor self-excited vibration caused by steam vortex, which is usually called air-flow excitation (flow excited vibrations) or gap excitation. As the phenomenon of air-flow vibration and oil film vibration phenomenon is similar, especially in the unit load phase occurs when the low-frequency vibration, more suspicious is due to the air-induced vibration caused. Domestic 200,000 kilowatts and 300,000 dry-tile units, the initial production has also encountered in the load phase of low-frequency vibration. According to the field analysis of a 200 MW unit, it is suspected that the air-flow excitation is one of the reasons. However, according to the current understanding, although it is not considered to be an air-flow exciting phenomenon, the air-flow excitation is indeed the current A problem worth attention. However, there are still few articles in China on the introduction of air-induced vibration. In order to find out the difference between air-flow vibration and oil-film vibration, this paper intends to give a brief introduction of the phenomenon, mechanism and elimination of air-flow excitation, and puts forward a preliminary view on the possibility of generating air-flow vibration in large domestic units. Large units put into operation, can cause the attention of this issue.