混流式水轮机出口旋流与尾水管涡带关系分析

为在设计过程中预测尾水管涡带，分析混流式水轮机转轮出口旋流与尾水管涡带之间关系，通过三维非定常雷诺时均值法对一个180 m水头段的混流式水轮机在三种典型工况下进行数值模拟分析，在数值模拟的基础上可视化尾水管涡带形状，并与模型试验的结果进行比较，验证模拟尾水管涡带方法的正确性。通过对典型工况下转轮出口速度、出口旋流数和涡带形状等来分析转轮出口旋流与尾水管涡带的关系，同时分析在尾水管锥段内旋流数轴向变化规律。结果表明：转轮出口旋流数随运行流量减小而增大，当转轮出口旋流数大于临界值时，尾水管内形成螺旋形涡带及低速区与回流；旋流数小于临界值时，尾水管内无明显涡带产生。

Analysis on the relationship between swirling flow at outlet of a Francis turbine runner and vortex rope inside draft tube

In order to predict the vortex rope during the design process for hydro turbine, the relationship between the runner outlet’s swirling flow of Francis turbine and the vortex rope inside the draft tube was analyzed. A 180-meter head Francis turbine is numerically simulated under three typical operating conditions by using the Reynolds-averaged Navier-Stokes (RANS) equations. The shape of vortex rope visualizations was compared with the results of the model test for verifying the correctness of simulation. Then, the swirl number, the velocity profile of runner outlet and the swirl number along the centerline of draft tube cone was analyzed to explain vortex rope formation under typical conditions. The results show that the swirl number at outlet of runner increase with the decrease of operating flow rate. When the swirl number at the outlet of the runner is greater than the critical value, the helical vortex rope, the low velocity zone and the backflow are formed in the draft tube. Meanwhile, when the swirl number is less than the critical value, there is no obvious vortex rope forming in the draft tube.