水泵水轮机S特性区能量损失及流动特性研究

为了调节电网的稳定性，抽水蓄能电站需要频繁启停和变换工况运行，导致水泵水轮机容易进入S特性区，机组振动增加，并网失败。本文以模型水泵水轮机为研究对象，采用熵产理论详细分析了S特性区不同工况下的能量损失规律，明确了熵产率分布与内部流动结构的关系。结果表明：S特性区内近飞逸工况总熵产最大，约为设计工况的5.1倍，脉动熵产占据的比例接近80%，随着流量的减小，转轮熵产占比逐渐降低，活动导叶和尾水管的熵产占比增加。小流量工况转轮进口靠近下环位置首先出现了明显的漩涡，导致了活动导叶出口和转轮进口的高熵产区，随着流量进一步减小，漩涡逐渐向上冠转移，并且切向速度增大，在转轮进口形成挡水环，阻碍水流进入转轮，在无叶区内出现了环状分布的高熵产区。反水泵工况，水流在低压边与逆时针旋转的叶片撞击，导致水流很难进入叶片内部，形成了大尺度的回流涡结构;双列叶栅内充满大量涡结构，导致活动导叶吸力面的熵产率增大，并且向固定导叶传播。

Energy loss and flow characteristics analysis of a model pump turbine in the S-shape region

In order to adjust the stability of the power grid，the pumped storage power station needs to start and stop frequently and operate under different working conditions.The pump turbine easily enters to the S characteristic region，which leads to the increase in unit vibration，and the unit interconnected failure.A model pump turbine was set as the research object in this paper.The entropy production theory was used to analyze the energy loss laws under different operating conditions in the S-shape region，and the relationship between the entropy production distribution and the internal flow structure was clarified.The total entropy production near the runaway condition is the largest，which is about 5.1 times of that in the design condition.The proportion of fluctuation entropy production is close to 80%.As the discharge decreases，the proportion of runner entropy production gradually decreases，while the proportion of guide vane and draft increases.There is a significant vortex first appeared near the shroud of the runner inlet，leading to a high entropy production area in the vaneless region.The vortex gradually developed towards the hub and the tangential velocity increased when the pump turbine operates in the turbine break condition.A water ring was formed at the runner inlet，hindering the water flow into the runner.A high entropy production region with circular distribution appeared in the vaneless region.Under the reverse pump condition，the water flow collides with the counterclockwise rotating blades at the low-pressure side，which makes it difficult for the water to enter the interior of the blades and forms a large-scale reverse vortex structure.The double row cascade is filled with a large number of vortex structures，leading to an increase in the entropy production rate of the guide vane，and propagated towards the stay vane.