混流式水轮机卡门涡致振机理探讨与分析

水轮机出现卡门涡后易引起振动等问题。许多安装混流式水轮机的水电站发生卡门涡频率的强烈振动，严重时甚至造成转轮叶片裂纹破坏，学界多认为这是由卡门涡共振引起。本研究通过比较卡门涡频率和固有频率的巨大差异、大朝山电站转轮叶片减薄修型后强振工况向大负荷转移等事实，提出新观点：大多数卡门涡强振及其破坏并非由共振引起。本研究进行了模型水轮机卡门涡观测试验，比较了流量、空化系数对可见卡门涡的影响，发现可见卡门涡多发生于大流量工况或低空化系数导致的涡心压力较低时，指出卡门涡由其涡心空化造成。通过电站消除卡门涡危害的措施等进一步说明：卡门涡共振存在于小流量工况，但共振能量低，没有显著破坏性;大流量工况的卡门涡强振并非共振，而源于卡门涡空化空腔溃灭产生的巨大冲击力。

Exploration and analysis of the mechanism of Karman vortex induced vibration in Francis turbine

Karman vortices in hydraulic turbines may generate vibration and other issues.Strong Karman vortex frequency vibration, found at a number of hydropower plants equipped with Francis turbines, and in some cases causing cracks in runner blades, is widely regarded as Karman vortex resonance by several studies.This study revealed a significant difference between the Karman vortex frequency and the natural frequency of the runner blade, and a new perspective was proposed based on the specific practice of reducing Karman vortex frequency vibration in Dachaoshan Power Station by decreasing trailing edge thickness, indicating that resonance was not the primary cause of strong vibration even when the vibration frequency was the Karman vortex frequency.The impact of discharge and cavitation coefficient on visible Karman vortices was examined in a model turbine Karman vortex observation test.Visible Karman vortices were discovered easier to form in circumstances with larger discharge or lower cavitation coefficient.It was noted that Karman vortices became visible only when cavitation occurred in the vortex core.The analysis of effective vibration reduction operations revealed that Karman vortex resonance does exist at low flow conditions, but it was not noticed due to the small vibration amplitude;and the strong Karman vortex frequency vibration at high flow conditions was caused by a massive impact force formed by the collapse of cavity bubbles rather than resonance.