叶顶间隙对贯流式水轮机空化流场的影响
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摘要
为了研究空化流动下灯泡贯流式水轮机中叶顶间隙数值变化对其压力脉动特性的敏感性,揭示不同叶顶间隙值对灯泡贯流式水轮机非定常流动特性的影响.以某电站原型机为研究对象进行全流道数值计算和模型试验研究,用4种间隙δ变化方案对压力脉动特性进行比较.分析了叶顶间隙处的流场结构,并对数值计算结果和模型实验结果进行了对比.结果表明:文中所使用的方法可以基本反映出水轮机内部的流动情况;当空化系数开始降低时,水轮机的效率发生变化,水力性能降低,达到临界空化系数时,效率下降明显;受到空化加剧的影响,叶片背面处监测点的压力脉动幅值增加,靠近轮缘处幅值大于叶片中部和轮毂处,当局部压力降到空化压力以下时波动不再剧烈,"削波"现象产生;随着叶顶间隙值的增加,转轮间隙处空化程度加剧,空化形态由间隙空化演变为翼型空化,并出现泄漏涡空化;叶片反面轮缘处压力脉动主频与叶片转频相差不大,较大的叶顶间隙值可以有效降低轮缘处高频压力脉动,然而泄漏流动加剧会导致空化更为严重.因此,选取的叶顶间隙数值对于灯泡贯流式水轮机在稳定运行和降低振动噪声方面具有重要的意义.
In order to study the characteristics of the pressure fluctuation of bulb tubular turbine effected by tip clearance under the cavitation flow and to reveal the various tip clearance of bulb tubular turbine influence on the unsteady flow,numerical calculation and model test research prototype on whole flow passage are used to compare with pressure fluctuation characteristics on the four clearance schemes on the basis of the SST k-ω turbulence model and moving mesh. Then the tip clearance of the flow field structure is analyzed and the numerical results and model experimental results which confirmed the method can basically reflect the internal flow of the turbine are compared.The results show that with the reduction of the cavitation coefficient,the energy of the water turbine characteristics change,and hydraulic performance degraded too. And the arrival of the critical cavitation coefficient leads to efficiency to drop significantly; affected by the occurrence of cavitation intensification,pressure fluctuation amplitude is increased in the suction side,and the nearby flange of the amplitude is greater than that in the middle part of the blade and hub. When the partial pressure drops below the saturation pressure,fluctuation is no longer violent,with the phenomenon called "clipping"appearing. With the tip clearance value and cavitation occurrences aggravating in the gap,cavitation shape evolves from a gap cavitation to an airfoil one,and then leakage vortex cavitation emerges. The rotating frequency dominates the pressure fluctuation of the nearby flange on the suction side of the blade,a larger tip clearance can reduce high frequency pressure fluctuation at the flange,leakage flow will lead to more severe cavitation. Therefore,selecting the appropriate value gap is greatly significant to the bulb turbine in stable operation,lower vibration and noise.
In order to study the characteristics of the pressure fluctuation of bulb tubular turbine effected by tip clearance under the cavitation flow and to reveal the various tip clearance of bulb tubular turbine influence on the unsteady flow,numerical calculation and model test research prototype on whole flow passage are used to compare with pressure fluctuation characteristics on the four clearance schemes on the basis of the SST k-ω turbulence model and moving mesh. Then the tip clearance of the flow field structure is analyzed and the numerical results and model experimental results which confirmed the method can basically reflect the internal flow of the turbine are compared.The results show that with the reduction of the cavitation coefficient,the energy of the water turbine characteristics change,and hydraulic performance degraded too. And the arrival of the critical cavitation coefficient leads to efficiency to drop significantly; affected by the occurrence of cavitation intensification,pressure fluctuation amplitude is increased in the suction side,and the nearby flange of the amplitude is greater than that in the middle part of the blade and hub. When the partial pressure drops below the saturation pressure,fluctuation is no longer violent,with the phenomenon called "clipping"appearing. With the tip clearance value and cavitation occurrences aggravating in the gap,cavitation shape evolves from a gap cavitation to an airfoil one,and then leakage vortex cavitation emerges. The rotating frequency dominates the pressure fluctuation of the nearby flange on the suction side of the blade,a larger tip clearance can reduce high frequency pressure fluctuation at the flange,leakage flow will lead to more severe cavitation. Therefore,selecting the appropriate value gap is greatly significant to the bulb turbine in stable operation,lower vibration and noise.
引文
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[16]王岩.轴流定桨式水轮机轮缘间隙对转轮性能影响的分析研究[D].兰州:兰州理工大学,2008.
[17]陈钱.叶轮机械相关流动中几种湍流模型的预测性能[D].北京:清华大学,2007.
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[19]敏政,李秋桐,李琪飞,等.灯泡贯流式水轮机尾水管流动特性分析[J].中国农村水利水电,2015(12):152-157.MIN Zheng,LI Qiu-tong,LI Qi-fei,et al.The analysis of the flow characteristic of draft tube based on cavitation flow of bulb turbine[J].China Rural Water&Hydropower,2015(12):152-157.
[20]国家技术监督局.水轮机模型验收试验规程:GB/T15613—1995[S].北京:水利电力出版社,1996.
[21]楚清河,王玲花,杨建设.水轮机效率换算公式的探讨[J].水力发电,2005,31(2):51-53.CHU Qing-he,WANG Ling-hua,YANG Jian-she.A discussion on efficiency conversion formula of hydraulic turbines[J].Water Power,2005,31(2):51-53.
[22]ZHANG Y,LIU K,XIAN H,et al.A review of methods for vortex identification in hydroturbines[J].Renewable and Sustainable Energy Reviews,2017(7):1-11.
[23]徐洪全,王万鹏.水轮机空化系数对及其对水力性能的影响[J].大电机技术,2010(5):44-48.XU Hong-quan,WANG Wan-peng.Cavitation coefficient of turbine and it’s effect to hydraulic performance[J].Large Electric Machine&Hydraulic Turbine,2010(5):44-48.
[2]LIU S H,SHAO J,WU S F,et al.Humerical simulation of pressure fluctuation in Kaplan turbine[J].Science in China Series E:Technological Sciences,2008,51(8):1137-1148.
[3]KIM You-taek,NAM Sang-hyun,Cho Y T,et al.Tubulartype hydroturbine performance for variable guide vane opening by CFD[C]∥Proceedings of the 5th International Conference on Fluid Mechanics.Shanghai:Chinese Society of Theoretical and Applied Mechanics,2007:424-427.
[4]夏林生,程永光,张晓曦,等.灯泡式水轮机飞逸过渡过程3维CFD模拟[J].四川大学学报(工程科学版),2014,46(5):35-41.XIA Lin-sheng,CHENG Yong-guang,ZHANG Xiao-xi,et al.3D CFD simulation of the runaway transients of bulb turbine[J].Journal of Sichuan University(Engineering Science Edition),2014,46(5):35-41.
[5]钱忠东,魏巍,冯晓波.灯泡贯流式水轮机全流道压力脉动数值模拟[J].水力发电学报,2014,33(4):242-249.QIAN Zhong-dong,WEI Wei,FENG Xiao-bo.Numerical simulation of pressure pulsation in the whole flow passage of bulb turbine[J].Journal of Hydroelectric Engineering,2014,33(4):242-249.
[6]夏晨宇,李龙,朱多彪,等.基于大涡模拟的贯流式水轮机压力脉动分析[J].中国农村水利水电,2015(2):143-147.XIA Chen-yu,LI Long,ZHU Duo-biao,et al.An analysis of pressure pulsation of the tubular turbine based on large eddy simulation[J].China Rural Water&Hydropower,2015(2):143-147.
[7]GONG Ruzhi,WANG Hongjie,LIU Wanjiang,et al.Numerical simulation and experimental study of the pressure fluctuation in water turbines[C]∥Proceeding of ASME2010 3rd Joint US-European Fluids Engineering Summer Meeting Collocated with 8th International Conference on Nanochannels,Microchannels,and Minichannels.Fairfield:ASME,2010:167-172.
[8]LI Zhangchao,CHANG Jinshi,JI Xingying,et al.Hydraulic disturbance method to reduce the pressure fluctuation in francis turbine draft tube[C]∥Proceeding of ASMEJSME-KSME 2011 Joint Fluids Engineering ConferenceSymposia-Parts A.Fairfield:ASME,2001:649-653.
[9]LIU Shuhong,LI Shengcai,WU Yulin.Pressure fluctuation prediction of a model Kaplan turbine by unsteady turbulent flow simulation[J].Journal of Fluids Engineering,2009,131(10):1102-1111.
[10]朱文龙,周建中,夏鑫,等.基于水电机组运行工况的水轮机压力脉动诊断策略[J].振动与冲击,2015,34(8):26-40.ZHU Wen-long,ZHOU Jian-zhong,XIA Xin,et al.A novel diag-nosis strategy for hydraulic turbine pressure pulsation based on operating state of a hydroelectric generating unit[J].Journal of Vibration and Shock,2015,34(8):26-40.
[11]THAITHACHA Sudsuansee,UDOMLIAT Nontakaew,YODCHAI Tiaple.Simulation of leading edge cavitation on bulb turbine[J].Songklanakarin Journal of Science and Technology,2011,33(1):51-60.
[12]PIERRE Duquesne,YVAN Maciel,CLAIRE Deschênes.Investigation of flow separationin a diffuser of a bulb turbine[J].Journal of Fluids Engineering,2016,138(1):1102-1111.
[13]NECKER J,ASCHEN BRENNER T.Model test and CFD calculation of a cavitating bulb turbine[C]∥Proceedings of the 25th IAHR Symposium on Hydraulic Machinery and Systems.Bristol:IOP Publishing,2010:1-10.
[14]冯建军,罗兴锜,吴广宽,等.间隙流动对混流式水轮机效率预测的影响[J].农业工程学报,2015,31(5):53-58.FENG Jian-jun,LUO Xing-qi,WU Guang-kuan,et al.Influence of clearance flow on efficiency prediction of Francis turbines[J].Transactions of the Chinese Society of Agricultural Engineering,2015,31(5):53-58.
[15]武桦,冯建军,吴广宽,等.轮毂间隙对轴流转桨水轮机性能影响的研究[J].水力发电学报,2014,33(1):185-190.WU Hua,FENG Jian-jun,WU Guang-kuan,et al.Study on effects of hub clearance flow on Kaplan turbine performance[J].Journal of Hydroelectric Engineering,2014,33(1):185-190.
[16]王岩.轴流定桨式水轮机轮缘间隙对转轮性能影响的分析研究[D].兰州:兰州理工大学,2008.
[17]陈钱.叶轮机械相关流动中几种湍流模型的预测性能[D].北京:清华大学,2007.
[18]MENTER F R.Two-equation eddy-viscosity turbulence models for engineering applications[J].AIAA Journal,1994,32(8):1598-1605.
[19]敏政,李秋桐,李琪飞,等.灯泡贯流式水轮机尾水管流动特性分析[J].中国农村水利水电,2015(12):152-157.MIN Zheng,LI Qiu-tong,LI Qi-fei,et al.The analysis of the flow characteristic of draft tube based on cavitation flow of bulb turbine[J].China Rural Water&Hydropower,2015(12):152-157.
[20]国家技术监督局.水轮机模型验收试验规程:GB/T15613—1995[S].北京:水利电力出版社,1996.
[21]楚清河,王玲花,杨建设.水轮机效率换算公式的探讨[J].水力发电,2005,31(2):51-53.CHU Qing-he,WANG Ling-hua,YANG Jian-she.A discussion on efficiency conversion formula of hydraulic turbines[J].Water Power,2005,31(2):51-53.
[22]ZHANG Y,LIU K,XIAN H,et al.A review of methods for vortex identification in hydroturbines[J].Renewable and Sustainable Energy Reviews,2017(7):1-11.
[23]徐洪全,王万鹏.水轮机空化系数对及其对水力性能的影响[J].大电机技术,2010(5):44-48.XU Hong-quan,WANG Wan-peng.Cavitation coefficient of turbine and it’s effect to hydraulic performance[J].Large Electric Machine&Hydraulic Turbine,2010(5):44-48.