基于熵产理论的水轮机尾水管涡带研究

Entropy production analysis for vortex rope of a turbine model

为了研究水泵水轮机部分负荷工况尾水管涡带产生的原因和压力脉动特性,本文以模型水泵水轮机为研究对象,对内部流动进行了全流道三维数值模拟并采用熵产理论进行了分析。计算结果分析表明:数值模拟与实验值吻合较好;固定导叶和蜗壳内的总熵产很小,而转轮和尾水管内较大,在小流量工况叶片压力面产生的流动分离会导致高熵产率分布区域的出现,并且会随着流量的进一步减小而扩大;在部分负荷出现了粗壮型和纤细形两种涡带,均呈现螺旋形,涡带的形成与叶片出口环量偏离零环量有很大关系;涡带的出现会在尾水管内形成漩涡,阻塞尾水管通道,涡带跟随转轮同方向旋转,但是转速更低,因此尾水管出现幅值较大的低频压力脉动。

In order to study the causes and pressure pulsation characteristics of the vortex rope under the partial load condition of the pump turbine,the model pump turbine was set as the research object in this paper. Both the steady and unsteady three-dimensional numerical simulation was carried out to simulate the internal flow,which was analyzed by the entropy production theory further. The results show that the numerical simulation is in good agreement with the experimental data. The entropy production in the scroll and stay vane is very small,while it is greater in the runner and draft. The flow separation produced on the pressure surface in the small discharge condition and it leads to the appearance of the high entropy production rate distribution area. And the area will expand as the discharge is further reduced. There are two kinds of vortex ropes with strong and fine shape at partial load,which are all spiral. The formation of the vortex rope has a great relationship with the circulation of the blade outlet n deviating from the zero. The appearance of the vortex rope will form a vortex in the draft tube,blocking the draft tube passage. The vortex rope will rotate in the same direction with the runner,but the rotation speed is lower,resulting in low frequency pressure pulsation with large amplitude in the draft tube.