水泵水轮机甩负荷过渡过程中的压力脉动和转轮受力

水泵水轮机甩负荷过渡过程中,压力脉动和转轮受力剧烈变化,导致事故频发。本文采用动网格技术对某模型水泵水轮机的甩负荷过渡过程进行全流道三维数值模拟,分析了水轮机压力脉动和转轮受力变化特性及其演变的内流机理。结果表明:甩负荷过渡过程中,转轮进口回流的出现和发展显著增加了无叶区内流体的湍动能,使导叶与转轮之间的动静干涉明显增强,导致压力脉动幅值急剧上升,其最大值达到初始阶段的5倍以上;与此同时,转轮进口局部产生的回流使无叶区内的湍动能和压力脉动强度在高度方向不均匀分布;此外,转轮进口回流发展使叶道内流态分布失衡,产生低频旋转失速,导致转轮叶片所受力矩和径向力的波动幅值快速上升,最大波动幅值分别达到初始阶段的10倍和60倍,而尾水管涡带对其的影响处于次要地位。

Transient pressure fluctuations and runner loadings of a model pump-turbine during a load rejection process

During the load rejection process of pump-turbines, the pressure fluctuations and runner loadings force change sharply, resulting in frequent accidents. In this paper, the dynamic grid technique was used to simulate the load rejection process of a model pump-turbine,and the change characteristics of pressure fluctuations and unstable forces acting on the runner were analyzed. The results show the emergence and development of backflow patterns at the runner inlet greatly increase the turbulent kinetic energy of the fluid in the vaneless space,which enhance the rotor-stator interaction between the guide-vanes and the runner blades sharply,leading to a sharp rise in the amplitude of the pressure fluctuations. The maximum amplitude of pressure fluctuations is more than 5 times that of the initial stage. The turbulent kinetic energy of the local fluid in the vaneless space is enhanced by the backflows at the hub side of runner inlet, which make the distribution of high frequency components of pressure fluctuations along the height uneven. The backflows at runner inlet lead to non-uniform flows and rotating stall within the runner channels, which is the main reason for the rapid rises of the fluctuations of runner torque and radial force. Both their maximum amplitudes raise up to about 10 times and 60 times those of the initial stage. However,the influence of vortex rope in the draft tube is secondary.