Hydrodynamics of a Pump-Turbine Operating at Off-Design Conditions in Generating Mode: Experimental Investigation
Hydrodynamics of a Pump-Turbine Operating at Off-Design Conditions in Generating Mode: Experimental Investigation
复制标题
DOI：
10.5075/epfl-thesis-5373
复制
发表时间：
2011
期刊：
影响因子：
--
通讯作者：
V. Hasmatuchi;M. Farhat;S. Roth;F. Botero;F. Avellan
中科院分区：
文献类型：
--
作者：
V. Hasmatuchi;M. Farhat;S. Roth;F. Botero;F. Avellan
现代水泵水轮机需要在抽水模式和发电模式之间频繁切换，并在非设计条件下长时间运行。根据水泵水轮机的具体转速，导叶恒定开度时的排出转速和扭矩转速特性可以呈“S”形。在这种情况下，机器运行在失控速度及以上时可能会变得非常不稳定，结构振动和噪声显着增加。在目前的工作中，对低比速径流式水泵水轮机比例模型的流体动力学进行了实验研究，该模型在10°导叶开度角（见图1）的发电模式下在失控条件下运行不稳定。使用气泡注入对定子中的壁压力进行测量，并与叶轮和导叶之间的无叶片间隙中的高速流动可视化同步进行。 Hasmatuchi* 等人提出了详细分析。 (2011) 的重点是当机器从最佳效率点 (BEP) 进入失控和涡轮制动模式时流量不稳定的发生。在这些严酷的操作条件下，发现覆盖约一半无叶间隙圆周的一个失速单元与叶轮一起以次同步速度（约叶轮旋转频率的 70%）旋转，这是在几个连续叶轮通道中产生的旋转流分离的影响，导致其堵塞。高速电影揭示了 BEP 导叶通道中相当均匀的流动模式，而在失速时，流动受到旋转失速通道的高度干扰；在低正流量时，情况更加严重，在失速通道期间，导流叶片通道中会产生回流和涡流（见图 1）。然后，详细介绍并应用特定的图像处理技术，使用所获取的高速可视化，针对低正放电操作点，创建整个导叶圆周上流动模式的合成瞬时视图。
Modern pump-turbines are subject to frequent switching between the pumping and generating modes with extended operation under off-design conditions. Depending on the specific speed of the pump-turbine, the discharge-speed as well as torque-speed characteristics at constant guide vanes opening can be “S-Shaped”. In this case, the machine operation may become strongly unstable at runaway speed and beyond, with a significant increase of structural vibrations and noise. In the present work, hydrodynamics of a low specific speed radial pump-turbine scale model experiencing unstable operation at runaway condition in generating mode for 10° guide vanes opening angle (see Figure 1) is experimentally investigated. Measurements of wall pressure in the stator synchronized with high-speed flow visualizations in the vaneless gap between the impeller and the guide vanes using air bubbles injection are performed. Detailed analysis presented in Hasmatuchi* et al. (2011) is focused on the onset of the flow instabilities when the machine is brought from best efficiency point (BEP) to runaway and turbine brake mode. At these severe operating conditions, one stall cell covering about half of the vaneless gap circumference is found to rotate with the impeller at subsynchronous speed (about 70% of the impeller rotational frequency), being the effect of rotating flow separations developed in several consecutive impeller channels that lead to their blockage. High-speed movies reveal a quite uniform flow pattern in the guide vanes channels at BEP, whereas at runaway the flow is highly disturbed by the rotating stall passage; the situation is even more critical at low positive discharge, where backflow and vortices develop in the guide vanes channels during the stall passage (see Figure 1). Then, a specific image processing technique is detailed and applied to create a synthetic instantaneous view of the flow pattern on the whole guide vanes circumference, for a low positive discharge operating point, using the acquired high-speed visualizations.