异常低水头对水泵水轮机压力脉动的影响

为研究水泵水轮机在异常低水头时的压力脉动特性,采用Realizable k-ε湍流模型对水泵水轮机运行于低水头的4个工况点进行了非定常数值计算,得到了蜗壳进口、导叶后转轮前、尾水管的锥管上游和肘管内侧4个监测点的压力信号,并与试验结果进行对比.重点考察了导叶开度37 mm、单位流量0.865 m³/s工况点的压力脉动时域和频域特征.研究结果表明:在异常低水头下,Realizable k-ε湍流模型能够精确地模拟大开度时水泵水轮机的压力脉动;蜗壳入口的压力脉动比较紊乱,在机组刚开启阶段脉动值较大,蜗壳进口压力脉动主频为转频19.78 Hz,说明在此工况下水泵水轮机蜗壳进口的压力脉动受到下游转轮转动的影响;导叶与转轮之间无叶区的压力脉动受到转轮与活动导叶之间的动静干涉作用,呈周期性变化且其主频为叶片通过频率;由于尾水管内部流动及涡带的作用,尾水管内的压力脉动为低频脉动,其主频约为0.35倍转频.

Influence of abnormally low head on pressure fluctuation of pump turbine

In order to study the pressure fluctuation characteristics of a pump turbine under the abnormally low head, Realizable k-ε turbulence model is used to simulate the unsteady flow of four opera-ting points. The pressure signals of the four monitoring points,i.e. in the inlet of spiral casing, after the guide vanes and before the runner, in the upstream of the draft tube cone and inside the draft tube elbow, are achieved and compared with the experimental results. And then, the pressure signals under the operating condition a₀=37 mm and Q₁₁=0.865 m³/s are analyzed in the time domain and frequency domain respectively. It is concluded that Realizable k-ε turbulence model can accurately si-mulate the pressure fluctuation in the larger guide opening of pump turbine. The pressure fluctuation of the inlet of the spiral casing is relatively disorder. When the unit is just open, the pressure fluctuation value is relatively great. The main frequency of pressure fluctuation in the inlet of the spiral casing is 19.78 Hz, equal to the rotational frequency,showing that in this condition, the pressure fluctuation in the inlet of spiral casing of the pump turbine is influenced by the rotating of the runner in the downstream. Because the pressure fluctuation in the vaneless space between the guide vane and the runner is affected by the static and dynamic interference, its change is periodic and main frequency is equal to the blade passing frequency. Owing to the internal flow and the vortex strip in the draft tube, the pressure fluctuation in the draft tube is a low-frequency fluctuation and its main frequency is 0.35 times the frequency of the runner passing through.