基于多路径传递的水电站厂房流激振动分析

Flow-induced vibration analysis of hydropower plant under two transfer paths

为研究水电站厂房流激振动传导机制,对振动传递路径进行了分析,采用重整化群(RNG)k-ε模型对混流式水轮机蜗壳、导叶、转轮及尾水管全流道进行了三维非定常湍流计算.基于湍流计算结果对转轮部件上的脉动压力进行了积分计算,给出了解析计算和数值模拟相结合的轴向水推力脉动特性计算方法,并沿着蜗壳/尾水管→厂房结构、转轮→轴系→机架基础→厂房结构这两条振动传递路径对厂房振动进行了计算分析.结果表明:整个流道内压力脉动程度较大的区域主要集中在尾水管直锥段以及弯肘段,频率主要为0.83和1.02 Hz,即转频的1/5和1/4,受尾水管低频涡带向上游传播影响,蜗壳区也出现了低频脉动压力;轴向水推力是机组垂直动荷载的重要部分,具有明显的脉动特性,转轮上冠与顶盖、转轮下环与基础环之间的空腔压力是形成轴向水推力的主要组成部分;蜗壳/尾水管→厂房结构这条振动传递路径是最直接也是作用最明显的,是厂房振动的主要诱因.

In order to investigate the flow-induced vibration transmission mechanism of powerhouse in hydropower station,the vibration-transmission path was studied by means of three-dimensional unsteady turbulent analysis,in which the renormalization group(RNG)k-εturbulence model was employed for the simulation of whole Francis turbine passage including spiral casing,guide vane,runner and draft tube.Based on the calculation results,the pulsating pressure acting on the runner was assessed through surface integral.In addition,a method by combining the analytical and numerical solutions for exploring the characteristics of pulsation of hydraulic axial thrust was presented.Moreover,the analysis of vibration occurring in power plant was conducted,with two vibration-transmission paths,namely volute/draft tube→powerhouse,runner→axis→generator pedestal→powerhouse taken into account.The results reveal that areas with intense pressure fluctuations are mainly concentrated in straight conical diffuser and elbow,the dominant frequency is 0.83 and 1.02 Hz,i.e.,one fifth and a quarter of the rotating frequency,respectively.Low-frequency pulsating pressure also appears in spiral casing due to upstream propagation of low-frequency draft tube vortex rope.The hydraulic axial thrust,which shows distinct pulsating characteristics,is a key component of the vertical dynamic load of the unit.The cavity pressures between crown and head cover,band and bottom ring are the main sources of the hydraulic axial thrust.The volute/draft tube→powerhouse vibration-transmission path is more direct and influential compared to the other,which is the major cause of powerhouse vibration.