【作者】 罗先武； 于安； 季斌；

【Author】 LUO Xian-wu;YU An;JI Bin;State Key Laboratory for Hydro-science and Hydro Engineering,Tsinghua University;School of Power and Mechanical Engineering,Wuhan University;

【机构】 清华大学水沙科学与水利水电工程国家重点实验室； 武汉大学动力与机械学院；

【摘要】 当水轮机运行在部分负荷工况时,尾水管中常出现强烈的涡带,严重时产生巨大的压力脉动,引发机组振动与噪声。本文主要采用数值模拟方法,通过分析不同通气情况下混流式水轮机内部非定常多相流动,探究水轮机尾水管中的漩涡运动特性,进而分析通气空化抑制水轮机水压脉动的机理和方法。为了提高计算精度,采用了基于密度修正的滤波器模型(FBDCM),并引入一种新的多相流模拟方法以反映通气空化过程中表面张力对流动的影响。经与实验比较,采用新的数值模拟方法预测的压力脉动频率与幅值更接近试验值,计算精度高于已有常规方法的数值精度,该方法可以更准确地再现水轮机尾水管内涡带的非定常运动特性。研究结果表明,在部分负荷通气工况下尾水管内存在两种性质不同的压力脉动:湍振(surge)引起的脉动成分,其频率略大于非通气工况下的涡带频率;空化湍振(cavitation surge)引起的脉动成分,其频率较涡带频率更低。该成分在尾水管肘部的脉动幅值明显大于其它位置。随着通气量增大,尾水管内压力分布趋于均匀化,涡带强度减弱、湍振脉动降低。当通气量达到4%时,水压脉动得到有效抑制。但通气不能改善空化湍振引起的压力脉动。更多还原

【Abstract】 When Francis turbine operated at part load conditions,there occurs strong vortex rope in the draft tube,which may induce violent pressure oscillation,and vibration and noise.The present paper aims to study the pressure fluctuation by analyzing the unsteady multiphase flow in the turbine draft tube using numerical simulation methods.In order to improve the numerical accuracy,a Level-set based method as well as FBDCM model are applied in the simulations.Compared with the results of the conventional method,the predicted frequencies and amplitudes of the pressure fluctuation by the present method are better and closer to the experimental data.That means the present method can reproduce the unsteady flow and reveal the vortex rope in the draft tube.The simulation results indicate that there are two outstanding components for the pressure fluctuation in the draft tube with air admission:1) The component due to the surge,whose frequency is a bit larger than the vortex rope fluctuation frequency without air admission;2) The component due to cavitation surge,whose frequency is less than the vortex rope fluctuation frequency.The component is the largest at the elbow of the draft tube.With air admission,the pressure distribution becomes homogeneous,the vortex rope and pressure vibration are alleviated.It should be noted that the pressure fluctuation due to cavitation surge cannot be improved by air admission.更多还原