水泵水轮机泵工况停机提前掉电流态分析

Flow analysis of pump turbine under power cutoff during its shutdown in pump mode

在水泵水轮机泵工况停机过程中,当活动导叶开度小于20%最大开度时,导水机构会出现异常振动和噪音。为了避免这种不稳定现象的发生,本文对水泵水轮机泵工况停机过程导叶小开度区流动进行数值模拟,分析了振动产生的水力学根源,验证了停机提前掉电是避免流动不稳定的有效措施。由于本文主要研究对象是活动导叶域的内部流动规律,导叶域的流动具有较强的周期性,故本文采用二维单周期模型进行计算。模拟过程中以电站过渡过程的计算结果作为数值模拟的边界条件,采用RNG k-ε双方程湍流模型进行求解,控制方程使用有限体积法进行离散,停机过程中活动导叶的关闭采用动网格技术实现。计算结果表明,在水泵水轮机停机过程中采用提前掉电,可以有效控制导叶内部流态,增强流动稳定性,明显降低了振动和异音产生的可能性。进一步分析表明,导叶域内部流动稳定性与断电开度大小成正相关,考虑到实际电站运行中的可操作性,本文推荐3°~6°为断电开度。

A pump turbine often experiences vibrations and abnormal noises from its distributor during pump mode shutdown from a guide vane opening less than the maximum opening of 20%.To eliminate this instability,we carry out numerical simulations of the transient flow in guide vane section,investigate variations in flow pattern during shutdown,and verify the necessity of power cutoff in advance.Twodimensional periodic simulations are adopted to consider periodicity in the flow and guide vane movement during shutdown,and a dynamic meshing technique is used to discretize the guide vane domain with a finite volume method and a RNG k-εtwo-equation turbulence model.The boundary conditions of 2 D modeling are specified using the results of transient calculation for the hydropower station.The results indicate that during a pump mode shutdown,the scheme of power cutoff in advance at an appropriate opening improves the stability of guide vane flow,thereby lowering the probability of generating vibrations and abnormal noises.Further analysis shows that the flow stability of guide vane channels is positively correlated with the opening threshold for power cutoff.And we suggest an opening threshold in the range of 3-6 degrees for practical operation of hydropower plants.