不同步导叶对混流式水轮机压力脉动的影响分析

Analysis of pressure pulsation in Francis hydraulic turbine with misaligned guide vanes

采用Realizable k-ε模型,对混流式模型水轮机三维全流道非定常湍流进行模拟,在实验验证的基础上,对不同步导叶(MGV)作用下的压力脉动进行了分析。选择部分负荷工况,分别研究MGV在5种不同开度下水轮机各过流部件的压力脉动特征。计算和实验结果表明:MGV不改变尾水涡带的旋转频率,随着MGV开度的变化,尾水管内主频和非主频的变化规律不同,甚至可能相反;转轮内的脉动主频为转轮转频与尾水涡带的旋转频率之差,其幅值变化规律与尾水管内脉动主频相同;MGV使转轮上出现了新的压力脉动频率,其值为转频与MGV数量的乘积,不同步导叶的开度偏离同步导叶开度越大,该频率的振动越强;在MGV作用下,各点主频脉动变化规律与采用同步导叶调节反映的规律是相似的,使用MGV装置可以在保证机组出力的条件下避开有害的压力脉动区。

In this paper,a simulation of the three-dismensional unsteady turbulent flow in the whole passage of a model Francis turbine by adopting a realizable k-ε turbulence model is presented.The model is verified by using experimental results,and pressure pulsation of the model turbine with misaligned guide vanes（MGV） device is calculated.Two MGV with five different MGV opening angles are chosen to analyze the influence of MGV on pressure pulsation in the spiral case,guide vanes,blades and draft tube.The computational and experimental results show that the rotational frequency of the vortex rope does not vary with MGV opening,while the amplitudes of differernt frequencies vary with MGV opening differently.The dominating frequency in the runner is the difference between the runner frequency and the rotational frequency of the vortex rope.A new frequency equal to the product of runner frequency and the number of MGVs appears in the runner,and the amplitude of this new pressure pulsation increases with the difference between the MGV opening and the other guide vanes opening.The MGV changes the peak-to-peak amplitude in the same way as the guide vanes without MGV,therefore,MGV can be adopted to ensure the stability of turbine with little changes of output.