基于弱可压缩计算的水泵水轮机超出力分析

为防止超出力工况下转轮内流体流速过高,出现脱流现象,进而导致无叶区压力脉动的升高,研究了水泵水轮机在超出力工况下运行时的水力稳定性.基于非定常、不可压缩流体,建立了三维水泵水轮机水力模型,采用SST k-ω模型对在110%额定功率下运行的模型机组进行数值模拟,预测超出力工况下的水泵水轮机内流场以及压力脉动,对导叶流域的压力脉动演化规律进行分析,并将其与试验结果进行对比.结果表明:在超出力工况下运行时,导叶附近流域压力脉动幅值沿流动方向逐渐增大;在固定导叶与活动导叶之间,压力脉动的主频大小由叶片通过频率的2倍变为1倍;2倍叶片通过频率分量幅值与混频幅值之比在活动导叶流域明显降低.超出力工况下,转轮叶片压力面出现脱流,并且在尾水管中存在1个粗大的涡带,导致机组性能降低.

Numerical simulation of excess output condition of a pump-turbine based on compressible calculation

The flow in the runner was speed up at the excess output condition,and flow separation may occur in the runner and the pressure fluctuation was amplified. To study the hydraulic instability of a pump-turbine at excess output condition,a 3D pump-turbine model was set up. Unsteady,incompressible flow was used for numerical simulation using SST k- ω turbulence model under 110% rated power condition. The inner flow as well as the pressure fluctuation in the pump-turbine was analyzed. The law of evolution of pressure fluctuation in the field between the casing and the runner was investigated.Calculation results were compared with the experimental data. The results show that the amplitude of pressure fluctuation increases along the flow direction near the region of vanes. The dominant frequency of pressure fluctuation changes into half of the two times of blade passing frequency between guide vanes and stay vanes. The ratio of the relative amplitude of 9 f n frequency to the amplitude of mixture frequency decreases in the domain of guide vanes. The separation flow at the pressure side in the runner,as well as a large vortex rope in the draft tube,can be found at excess output condition.