水泵水轮机极小开度反水泵工况压力脉动与内流特性分析

混流式水泵水轮机普遍存在S特性区,水轮机工况启动时机组常不能由空载直接带负载,容易进入反水泵区,导致机组并网困难。本文以模型水泵水轮机为对象,对极小导叶开度下的多个反水泵工况点进行了整体流道三维流动计算,探讨极小导叶开度下反水泵区机组的非定常流动特性。数值计算采用SAS SST-CC湍流模型,5个定常工况点计算的外特性曲线与模型试验数据吻合较好。对流量较小的工况进行非定常计算,旋转转轮9个叶道各8个测点的压力脉动结果显示,相似位置测点间的压力脉动混频幅值和频率均存在明显差异,峰峰值的差异最大达到4.2%,说明此时转轮内的流态分布很不均匀。测点离导叶越近,低频脉动的主频从0.19 fn逐渐增加到1.07 fn;动静干涉引起的20 fn脉动幅度会逐渐增强,但转轮出口位于出流与入流过渡区的测点趋势则不同。结果显示在反水泵工况区运行,转轮各叶道间的流态分布极不对称,充满了严重的流动分离和漩涡。

Unsteady flow and pressure pulse analysis of a Francis pump-turbine on reverse pump zone with small guide vane opening

The S-curve characteristic is widespread in pump-turbine. When the unit starts running under turbine-mode, the operating condition usually cannot be changed from no-load to full-load directly, which inevitably make the unit to enter reverse pump zone. This phenomenon brings difficulties for grid connec-tions. In this paper,a model pump-turbine was chosen for analysis. The three-dimensional numerical calcu-lation of the overall flow channel was carried out for the reverse pump mode under an extreme small guide vane opening. The simulations were performed with the SAS SST-CC turbulence model. The steady simulat-ed external characteristic parameter curves were in good agreement with the model test data for five operat-ing points. The operating point where the flow rate is relatively small was chosen for long-term unsteady flow calculations, where eight different points on nine runner blade to blade flow channel were chosen to monitor the pressure fluctuations. The results show that there exists a noteworthy difference of pressure peak-to-peak amplitudes and pulsation frequencies in each rotating flow passage. The largest peak-to-peak difference is up to 4.2%,which means that the flow distribution in the runners is not uniform for this con-dition. From points rva to rvh with those points closer to the guide vane,the main frequency of the pulsa-tion in the low frequency region is gradually increased from 0.19f_n to 1.07f_n; the pulsation amplitude caused by rotate and static interference (RSI) will gradually increase,but not for points rvg. The flow pat-tern shows that this points was located on outflow and the inflow transition zone of the runner blade out-flow channels. Flow pattern analysis indicates that the runner flow fields are asymmetrical in different blade passages under this revise pump condition,with significant flow separation and vortexes.