中低比转速混流式水轮机空化与水力振动分析

Analysis of Cavitation and Hydraulic Vibration for Middle and Low Specific Speed Francis Turbine

针对中低比转速水轮机空化、振动问题比较突出的现象,以大桥电站水轮机为例,采用分离涡模型(DES)对其进行了三维CFD计算,得到了活动导叶、转轮和尾水管内的压力分布、速度分布及压力脉动特性。结果表明,转轮空化发生在叶片出水边靠近下环的区域,与实际情况相符;机组在高水头、大开度工况下,振动更突出,振动频率为机组旋转频率的整数倍,表明振动主要由转轮造成,而非尾水管涡带引起的。

The detached eddy simulation （DES） is employed to simulate three-dimensional transient flow through the middle and low specific speed Francis turbine, and the pressure distribution, cavitation zones in the runner and the pressure pulsation information at the key positions in the draft tube are obtained. The results show that the cavitation occurs at the areas between the outlet of the runner blades and the runner band; the pressure pulsation amplitude in the draft tube is larger under the maximum water head and large guide opening; the hydraulic vibration frequency is the integral times of runner rotational frequency, which illustrates that the vibration is caused by the runner due to the improper design instead of the vertical band in the draft tube.