混流式水轮机所存在的水力不稳定问题，长期以来人们比较熟悉与关心的主要是尾水管涡带和卡门涡。但是随着混流式水轮机的不断发展，特别是近年来国内外一系列大型混流式水轮机的投产运行，陆续发现除尾水管涡带和卡门涡这些熟知的水力振动外，还存在一系列值得关注的水力不稳定现象，其中之一就是叶道涡。当水轮机偏离最优工况时，不仅在尾水管中央可以看到一条旋转的涡带，在转轮叶片间还可以看到有一连串的涡束沿着两个叶片间流出，这就是叶道涡。叶道涡起源于偏离最优工况后转轮上冠进口处的脱流。在高水头时(以设计水头为界)，脱流发生在上冠叶片进口的背面，此时的叶道涡可以称之为高水头叶道涡，或背面进口边(上冠)叶道涡；低于设计水头时，脱流发生在叶片正面进口边，此时的叶道涡可称之为低水头叶道涡或正面进口边叶道涡。从叶道涡产生的水力原理看，与尾水管涡带一样，所有混流式水轮机偏离最优工况后，必然要发生叶道涡。过去有一种观点，认为叶道涡分散在各个叶道内，难以形成合力，对稳定运行威胁不大。但是，当叶道涡发展比较严重时，可能会形成比较粗大的涡带，而且叶道涡的尾部相当不稳定，噪音比较大，可能会影响机组稳定运行。目前在混流式水轮机的模型试验中已经开始像对待尾水管涡带那样，要求注意观测与记录叶道涡。一些大型水轮机已要求躲开叶道涡区域运行。本文采用实验与数值模拟相结合的方法对大型混流式机组中的叶道涡诱发的压力脉动进行了研究。在与哈尔滨大电机研究所合作的实验研究中，针对原型水轮机和模型水轮机，在小流量工况下，采用应变电测法，测得了转轮叶片上的应变、应力随时间的变化。由实验结果可知，当转速不变的情况下，叶片上的应变频率不随流量的变化而变化，测得的应变频率等于叶道涡诱发的压力脉动的频率。采用数值模拟技术，在部分流量工况下（导叶小开度区），计算了包括导叶、转轮、尾水管在内的模型水轮机的内部流场。计算结果证明，叶道涡起源于流体进入转轮时偏离设计冲角的脱流，发生在靠近上冠转轮叶片的背面，确定了在转轮内部的压力脉动主要是由叶道涡诱发的，叶道涡频率为转轮的转动频率。将叶道涡与尾水涡进行比较，发现叶道涡诱发的压力脉动虽然振幅稍低，但是频率比较高。实验与计算同时证明了叶道涡的频率等于转轮的转动频率。

For a long period, vortex rope in draft tube and Karman vortex are believed to be the primary factor of stability violation. However, as huge Francis hydraulic turbines are widely used, other important factors, such as interblade vortices, are found to respond the stability violation. When Francis turbines are operated at off design conditions, not only vortex rope in the draft tube occurs but also the vortex bunches, which are called as interblade vortices, generate and flow out from the blades. Divided by the design head, interblade vortices can be separated to be high head interblade vortices and low head interblade vortices. When the turbine is operated at higher head, the high head interblade vortices are produced by flow separation at pressure side of the blade near the crown. When the turbine is operated at lower head, the low head interblade vortices are produced by flow separation at suction side of the blade near the crown.From the previous view, interblade vortices distribute at different channels. They are difficult to unite and have little influence to the stabilization. But if interblade vortices develop to strong vortex band, and the tail is unstable, the stabilization will be damaged and the noise will occur. Now interblade vortices are required to be observed and noted as the same as vortex in the draft tube. Many huge Francis hydraulic turbines are asked to avoid the interblade vortices zone.Experimental and numerical simulation methods are used to investigate the interblade vortices in this paper. The strain fluctuation on the blade of prototype and model Francis hydraulic turbine is measured by electric measure of strain-flake method on High Head Experimental Table II in Haerbin Big Electric Machine Factory. The experimental results show that the frequency of the strain fluctuation keeps constant when the mass flow changes. The CFD results of part load condition show that the interblade vortices occur at the suction side of the blades near the crown, because of the flow separation at the same locations. Compared with vortex in draft tube, the frequency of pressure fluctuation induced by interblade vortices is much higher. The experimental and CFD results prove that the frequency of pressure fluctuation induced by interblade vortices is equals to the rotational frequency.