三维非定常湍流尾水管涡带计算研究

混流式水轮机弯肘型尾水管在部分负荷工况下产生带气泡的尾水涡流, 涡流在离心力的作用下形成与水流共同旋的涡带，由此产生的低频压力脉动是混流式水轮机面临的一个普遍性问题。水轮机中存在的水力压力脉动现象将诱发转轮叶片疲劳破坏。更有甚者对整个机组、厂房构成威胁, 严重影响了机组的安全稳定运行。本文采用全流道三维非定常流动数值模拟方法, 研究三峡混流式水轮机在部分负荷工况运行时，由尾水管涡带以低频的周期在尾水管内旋进引起的压力脉动现象。采用全流道非定常流动粘性湍流计算，计算结果表明在各记录点都捕捉到了涡带低频压力脉动：频率为0.333Hz, 是转频1.25Hz的3.75分之一，相近工况模型试验实测涡带频率为5.31Hz, 是转频18.62Hz的3.51分之一，从涡带频率看计算结果与试验测量结果一致。

3-D unsteady Turbulent Vortex Rope Flow Simulation in Draft Tube of a Francis Turbine

Under work points of partial load, there will always be air bubble containing tail water vertex flow inside the elbow part of draft tube of Francis turbine. This vertex flow is liable to form a vortex rope in procession with the stream, which subsequently causes a low frequency pressure fluctuation that is a universal problem with Francis turbines. The existence of hydraulic pressure fluctuation is known to be the cause of the fatigue failure of runner blades. It will also badly work against the stable safety operation of the machine and eventually be a menace to the power unit and power plant. This paper is to present a numerical simulation method of integral flow passage 3-D unsteady flow, used to study the phenomenon of pressure fluctuation caused by the low frequency periodic procession of the tail water vortex rope inside the draft tube of the Three Gorges Francis turbines, under partial load work conditions. The results of the calculation of integral flow passage unsteady viscosity turbulent flow show that, the vortex rope caused low frequency pressure fluctuation occurs at each recorded point, which frequency is 0.333Hz, compared with the rotational frequency (1.25Hz ) 1: 3.75. The vortex frequency of actual measurement under similar work points is 5.31Hz, 1: 3.51 with the rotational frequency. So, the calculated result is consistent with that of the experiment in light of the vortex frequency.