泄水锥加长与主轴中心孔补水对水轮机尾水管流态的影响

Effect of runner cone length and shaft center hole water feeding on flow characteristics in draft tube

为了探究泄水锥加长与主轴中心孔补水对水轮机尾水管流态的影响,采用SST湍流模型对某混流式模型水轮机进行了全流道三维非定常模拟.对额定工况下原泄水锥、泄水锥加长这2种方案,以及对部分负荷工况下原泄水锥、泄水锥加长、泄水锥加长后补水这3种方案进行了计算.分析了不同方案下尾水管水流流线、尾水管各断面压力、尾水管涡带及流体的涡流黏度值的变化情况.结果表明:在额定工况下,泄水锥加长后对尾水管水流有稳流效果且水轮机效率略有提高;在部分负荷工况下,泄水锥加长后尾水管中心产生的涡带有变小的趋势,但涡带的偏心距稍有增加,而向尾水管补入2%额定流量的水流后,尾水管流态明显改善,直锥段水流的涡流黏度值降低,尾水管涡带的偏心距和涡带形态都有所减小,由偏心涡带引起的低频压力脉动幅值也有明显降低.

To investigate the effect of runner cone length and shaft center hole water feeding on flow characteristics of draft tube,the SST turbulence model was used to simulate the three-dimensional unsteady flow in a Francis turbine. Under the rated condition,two cases,i.e.,the original runner cone and a longer runner cone were simulated. Under the part-load condition,however,three cases were involved,namely,the original runner cone,the longer runner cone,and the longer cone with shaft center hole water feeding. The streamlines,pressure variations in various cross-sections in the tube,vortex rope and eddy viscosity of flow in these cases were analyzed. The results show that under the rated working condition the lengthened runner cone can intensify the stability of the flow in the draft tube and slightly improve the turbine efficiency. Under the part-load condition,the lengthened runner cone can reduce the size of vortex rope in the tube but increase the eccentricity of the rope a bit. After a 2% rated flow water feeding is applied to the draft tube,the flow characteristics are significantly improved,the eddy viscosity of the flow in the straight diffusion section is lowered. Both the eccentricity and the rope size are decreased,and the amplitude of low-frequency pressure pulsation caused by the eccentric vortex rope is considerably reduced.