Numerical simulation of hydrodynamics in a pump-turbine at off-design operating conditions in turbine mode
Numerical simulation of hydrodynamics in a pump-turbine at off-design operating conditions in turbine mode
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DOI：
10.1088/1755-1315/15/3/032041
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发表时间：
2012-11
期刊：
影响因子：
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通讯作者：
J. Yan;U. Seidel;J. Koutník
中科院分区：
文献类型：
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作者：
J. Yan;U. Seidel;J. Koutník
本文研究了径流式水泵-涡轮机缩尺模型在非设计工况下的水动力特性，包括小正流量下的飞逸和“S”型涡轮机制动曲线。它是一种低比转速的弗朗西斯式水泵水轮机，有9个叶轮叶片和20个固定叶片以及20个导叶。计算域包括从蜗壳进口到尾水管出口的整个水通道。完全结构化的六面体网格生成的商业软件ANSYS-ICEM。非定常不可压缩模拟使用商业代码ANSYS-CFX 13。对于湍流建模，应用标准k-ε模型。在不同的操作点的数值结果进行了比较，实验结果。预测的压力幅值与实验数据吻合较好，叶轮上的法向力幅值在合理范围内。详细的分析揭示了当机器从正常运行状态进入飞逸和涡轮机破裂模式时，流动不稳定性的开始。此外，旋转失速现象被很好地捕捉到在失控条件下，以及低流量运行条件下，一个失速细胞旋转的内部和周围的叶轮约70%的频率。此外，旋转失速被发现是在几个连续的叶轮通道，导致其堵塞的旋转流分离的效果。水泵水轮机S曲线特性的可靠模拟是变工况设计和优化的基本要求。
The hydrodynamics of a reduced-scaled model of a radial pump-turbine is investigated under off-design operating conditions, involving runaway and "S-shape" turbine brake curve at low positive discharge. It is a low specific speed pump-turbine machine of Francis type with 9 impeller blades and 20 stay vanes as well as 20 guide vanes. The computational domain includes the entire water passage from the spiral casing inlet to the draft tube outlet. Completely structured hexahedral meshes generated by the commercial software ANSYS-ICEM are employed. The unsteady incompressible simulations are performed using the commercial code ANSYS-CFX13. For turbulence modeling the standard k-ε model is applied. The numerical results at different operating points are compared to the experimental results. The predicted pressure amplitude is in good agreement with the experimental data and the amplitude of normal force on impeller is in reasonable range. The detailed analysis reveals the onset of the flow instabilities when the machine is brought from a regular operating condition to runaway and turbine break mode. Furthermore, the rotating stall phenomena are well captured at runaway condition as well as low discharge operating condition with one stall cell rotating inside and around the impeller with about 70% of its frequency. Moreover, the rotating stall is found to be the effect of rotating flow separations developed in several consecutive impeller channels which lead to their blockage. The reliable simulation of S-curve characteristics in pump-turbines is a basic requirement for design and optimization at off-design operating conditions.