水泵水轮机在S特性区的流态及压力脉动研究

Flow characteristics and pressure pulsation in the S characteristic area of model pump turbine

抽水蓄能机组的四象限特征曲线存在着S形曲线,抽水蓄能机组运行工况复杂,机组经常在多个工况之间转换,机组在水轮机和水泵状态之间频繁切换,都会穿越S形曲线。S特性可以导致水泵水轮机机组产生强烈的振动,使得机组并网困难,振动剧烈,甚至因压力超标严重影响电站的安全稳定运行。在业界的共同努力下,S形问题对工程投运影响已经得到了根本解决,但是S形问题的诱发机理并不十分清楚。因此该文以某模型水泵水轮机为研究对象,通过全流道非定常数值模拟和基于全特性试验的粒子图像测速法(particle image velocimetry,PIV)相结合,根据机组的运行特性,选取水泵水轮机三个开度下的13个工况点内部流动特性及压力脉动特性进行了研究。综合数值模拟及试验结果,获得空载工况,小流量工况及反水泵工况下无叶区漩涡的运动规律。分析了漩涡结构对无叶区压力脉动特性的影响。结果表明,空载工况对S特性区压力脉动幅频特性存在影响,空载工况与无叶区压力脉动存在必然联系。各工况点下无叶区压力脉动主频大部分工况为叶片通过频率,即9 f_(n)(f_(n)为转频),部分工况受尾水管压力脉动影响主频为0.66 f_(n)。通过计算和试验对比发现,无叶区漩涡结构的周期性运动对无叶区压力脉动的周向分布存在重大影响。

The four-quadrant characteristic curve of pumped storage units has a S-shaped curve.The operation conditions of pumped storage units are complex,the units often switch between multiple operating conditions,and the units frequently switch to turbine and pump modes,all of which will traverse the S-shaped curve.S characteristics can lead to strong vibration of the pump turbine unit,making it difficult to connect the unit to the grid,violent vibration,and even seriously affecting the safe and stable operation of the power station due to pressure overload.With the joint efforts of the industry,the impact on the S-shaped problem with the project commissioning has been fundamentally solved,but the triggering mechanism of the S-shaped problem is not very clear.In this paper,a model water pump turbine is taken as the research object,and the internal flow characteristics and pressure pulsation characteristics of the pump turbine at 13 operating points under three openings are investigated,through a combination of full-flow channel non-constant numerical simulation and particle image velocimetry(PIV)technique based on the full characteristic test.Comprehensive numerical simulation and experimental results,the motion law of the vortex under the no-load condition,low-flow condition and backwater pump condition without vane are obtained.The effect of the vortex structure on the pressure pulsation characteristics in the vaneless space is analyzed.The results show that the no-load condition has an effect on the amplitude-frequency characteristics of the pressure pulsation in the S characteristic zone,and the no-load condition is necessarily related to the pressure pulsation in the vaneless space.The main frequency of pressure pulsation in the bladeless area under each working point is the blade passing frequency for most working conditions,i.e.9 f_(n)(f_(n)is the rotation frequency),and the main frequency is 0.66 f_(n)for some working conditions influenced by the pressure pulsation in the tail pipe.It is found that the periodic motion of the vortex structure in the vaneless space has a significant influence on the circumferential distribution of pressure pulsation in the vaneless space through making a comparison between calculation and test.