可逆式水泵水轮机泵工况的驼峰特性

为了研究可逆式水泵水轮机泵工况的驼峰特性,通过非定常分离涡模拟（DES）的方法,计算不同流量工况下机组的内部流场特征.根据机组对应工况下的模型试验,对机组流道中的流态特征进行对比分析,特别对扩散流道损失以及转轮与导叶之间的动/静干涉现象进行研究,探讨驼峰特性产生的具体原因.结果表明：机组在小流量工况下运行时,转轮出口流动呈现明显非对称性;紊乱的流动特征引发转轮内部与扩散段中产生涡结构与二次流结构;由于不良流态的出现,过流部件水力损失显著上升,并引发扬程的下降,导致机组形成扬程-流量曲线的驼峰区域.因此,改善小流量工况下转轮内部流态对于改善水泵水轮机驼峰特性具有重要的作用.该研究内容阐明了驼峰特性对水泵水轮机造成不良影响的机理,对改进机组水泵工况的水力性能提供了参考与帮助,对于水泵水轮机的稳定运行具有重要意义.

Hump characteristic of reversible pump-turbine in pump mode

To investigate the hump characteristic in discharge-head curve of reversible pump-turbines in pump mode, the internal flow field of a pump-turbine unit is simulated in its pump mode under different flow-rate conditions by employing the detached eddy simulation （DES） method. The underlying mechanism for the hump characteristic is exploited by comparing the CFD and experimental characteristics of flow inside each passage of the unit, especially for the hydraulic losses in the diffusing passage and for the rotor-stator interaction. The results show that the flow exhibits an obviously asymmetric pat- tern at the runner outlet as the unit is operated in the low discharge range. The asymmetric flow field is caused from the vortex and secondary flow generated in the diffusing portion of the runner passages. As a result, the hydraulic losses in the unit rise dramatically, causing a reduction in the pump head, eventually the hump characteristic occurs. Nevertheless, improving the flow pattern under the low discharge conditions can be very helpful to mitigate or eliminate the hump characteristic. The mechanism for the hump characteristic has been enunciated here. This may be referential and helpful to improve the hydraulic performance and conducive to enhance the operating stability of a reversible pump-turbine.