【作者】 姬晋廷；

【导师】 罗兴锜； 廖伟丽；

【作者基本信息】 西安理工大学 ， 水利水电工程， 2009， 博士

【摘要】 我国有相当一部分轴流式水力机组空蚀破坏严重、运行稳定性差、综合性能指标较低,亟待改造,开展轴流式水轮机转轮改造中的关键问题研究对于改善机组的综合性能、提高低水头水能资源的利用效率以及提高水轮发电机组运行的可靠性具有非常重要的意义。本文结合CFD技术和流固耦合技术,开展了流动分析、动应力分析、流固耦合计算以及改型设计和性能预测等若干轴流式水轮机转轮改造中关键问题的研究工作。本文以轴流式水轮机为研究对象,进行了水轮机全过流部件的三维数值模拟,在此基础上,开展了轴流式叶片的动应力问题研究,进行了轴流式叶片的流固耦合分析,最后对湖北陆水水电站的轴流式转轮进行了改型设计和性能预测。(1)对轴流式水轮机的内部流动进行了全流道数值模拟,研究了运行工况对轴流式水轮机内部的流场分布的影响,分析了各过流部件表面的压力脉动情况以及非定常流动特性。定常流动的研究结果表明：固定导叶出口水流角在周向上分布的不均匀程度随水轮机流量的增大而增加；导叶区的流动要素沿周向分布的均匀性随导叶开度的增大逐渐减弱；大流量工况下,来流不均匀引起的各叶片表面压力分布的差异在轮毂处附近表现得最为明显,轮缘附近次之,各截面叶片间相差较大的地方均位于叶片前半部分。非定常流动的研究结果表明：不同工况下,相近时刻的导叶正背面压力分布趋势差异较大；导叶区压力脉动的主频含有与尾水管低频压力脉动相同的频率成分,在底环和中间点的压力脉动中还含有接近机组转频的频率成分；尾水管进口压力脉动的主频成分主要为低频成分,这种低频压力脉动是水轮机中压力脉动的主要脉动源之一；叶片表面的压力脉动频率除了低频成分外,还有机组转频倍数的中频成分,为机组的次要振动源。(2)对轴流式转轮和叶片分别进行了强度计算,对单叶片进行了动应力分析,分析了不同工况下轴流式转轮和叶片的应力分布特点及应力集中区,揭示了轴流式叶片动应力与流道内水压力脉动之间的关系。研究结果表明：在水压力的作用下,叶片上出现了3个应力集中区；整体转轮的最大应力值随叶片转角增大逐渐减小；随着叶片转角增大,叶片表面从轮毂至轮缘应力变化梯度逐渐增大,叶片表面应力分布不均匀程度增大。叶片动应力分析结果表明,叶片上最大应力点随工况和时间的不同在叶片压力面与法兰连接处靠近下游侧和叶片吸力面与法兰连接处靠近下游侧之间变化；叶片与法兰连接处存在高幅动应力明显大于叶片静应力的分析结果；叶片中部的应力波动比轮毂和轮缘严重,出水边比进水边明显；叶片上各点的动应力频率成分与流道内的水压力脉动频率基本一致,说明叶片上的高幅动应力主要由水压力脉动引起。(3)对轴流式转轮和叶片进行了振动特性分析,对叶片进行了流固耦合分析,研究了流固耦合作用对叶片区流场以及叶片应力分布的影响。研究结果表明,轴流式叶片在水中的固有频率有所降低,具有非线性的特点；考虑流固耦合作用后,叶片正背面压差增大,在一定程度上恶化了叶片的空化性能；考虑流固耦合作用后,叶片上的应力分布和最大应力出现的位置均未发生明显变化；与非定常流动计算结果相比,各时刻最大应力值和最大应变的变化情况各不相同；流固耦合作用不仅改变了叶片区的流场分布,对叶片的应力也有较大影响。(4)对湖北陆水水电站的轴流式转轮进行了改型设计与性能预测。通过对叶片翼型几何形状的优化,改善了转轮的水力性能；对改型后的转轮进行了性能预测,详细分析了改型后轴流式转轮主要工况的水力性能,绘制了转轮的定桨曲线、转桨的模型综合特性曲线以及最大水头下的导叶水力矩曲线。电站的实际运行情况表明,改型后转轮ZZX30的各项指标达到了改型目标提出的要求,效率高,出力稳定,综合性能有了较大提高,为电站创造了良好的经济效益,也说明了本文采用的改型设计方法和性能预测方法是有效的。更多还原

【Abstract】 A number of axial flow hydro-generating units suffer from serious cavitation damage, worse operation stability and bad overall performance. Study on the key issues of axial flow turbine runner’s transformation, in order to improve hydraulic turbine’s overall performance, to enhance the use efficiency of hydropower resources with low water head and reliability as well as economy of hydro-generating unit operation, has the very vital significance. In this paper, by means of CFD technology and fluid-structure interaction method, the research of certain key issues in the transformation of axial flow turbine runner were carried out, such as flow simulation, dynamic stress analysis, fluid-structure interaction calculation modification design and the performance estimate.Take the axial flow hydraulic turbine as the object of study; the dynamic stresses on the runner blade were analyzed on the basis of numerical simulation of three dimensional flow in entire hydraulic turbine overflow components. The fluid-structure interaction calculation of axial flow blade was conducted. Then the modification design and the performance estimate to axial flow runner blade of HuBei LuShui power plant were carried on.(1) The numerical simulation of the flow in the whole flow passage of axial flow hydraulic turbine was done. The influence of operation condition on the flow field was analyzed, as well as the pressure fluctuation on flow surface and unsteady flow characteristic.The results of steady flow simulation show that the nonuniformity of stay vanes out angle along the circumferential distribution becomes serious with increase of flow. With increase in the guide vane opening, the flow elements uniformity along the circumferential distribution in guide vane area gradually weakened. The distribution differences of water pressure on various runner blades caused by flow nonuniformity behaved most obviously nearby the hub, and blade flange took the second place. The distribution differences of cross section behaved more obviously on first half part of blade.The results of unsteady flow simulation show that under different operating conditions, the differences of pressure distribution tendency on press face and suction face of the guide vane in the similar moment are quite different; The basic frequency of the pressure fluctuation frequency in guide vane contains the same low frequency component within the draft tube’s; The pressure fluctuation frequency of bottom ring and the mid-point includes the close frequency components of rotation frequency. And the low frequency components of the pressure fluctuation frequency in draft tube inlet are one of the main sources in hydraulic turbine pressure fluctuation. Besides low frequency, intermediate frequency components close to multiple rotation frequency are also included in the pressure fluctuation frequency of the blade surface, and the secondary sources in hydraulic turbine pressure fluctuation.(2) Strength analysis of the axial flow runner and blade and dynamic stress analysis of single blade were carried on separately. The stress distribution characteristic and stress concentration zone on runner and blade are discussed under different operating conditions. The relationship between dynamic stress on axial flow blade and pressure fluctuation in flow channel was revealed.The results indicate that the blade have emerged on three areas of stress concentration under hydraulic pressure function; As the blade angle increases, maximum stress value of the overall runner decreases gradually, and the stress gradient on blade surface increases gradually from the wheel hub to the rim. It also reveals that uneven degree of stress distributes on the blade surface increases.The blade dynamic stress analysis results show that maximum stress appears on the junction of blade pressure surface as well as suction surface and the flange near the downstream side, and it changes between them in different time of the different conditions; The high amplitude dynamic stress in the junction of blade and flange is obviously larger than the result of static stress analysis. The stress changes in the central blade more seriously than in wheel hub and rim, and more obviously in outlet of blade than in inlet of blade; The dynamic stress frequency components of blade are basically the same as hydraulic pressure frequency in the flow passage, which indicates that the high amplitude dynamic stress is mainly caused by water pressure fluctuation.(3) The vibration characteristics of the axial flow runner blade were analyzed. The fluid-structure interaction calculation of axial flow blade was conducted. The influence of FSI on flow field of blade zone and stress distribution on blade was studied.According to calculation results, the natural frequency of blade in the water decrease with the characteristics of non-linear; the pressure difference between press side and suction side increases after considering the FSI, to a certain extent, which will worsen cavitations performance of the blade. Meanwhile, stress distribution on the blades does not change significantly. Comparing with the results of unsteady flow simulation, the change of maximum stress value and maximum strain value after considering the FSI differ from time points. The research demonstrates that the FSI not only changes the distribution of the flow field in blade area, but also have a greater impact on the stress of the blades.(4) The modification design and the performance estimate to axial flow runner blade of HuBei LuShui power plant were performed.By optimizing the airfoil of blade geometry to improve the hydraulic performance of the runner in the main operating conditions, the performance prediction of the modified runner was carried out, and the characteristic diagram of curves of fixed-blade propeller, the comprehensive characteristic diagram of curves of propeller blade and the hydraulic moment curve of guide vane under the maximal head were drawn up. The actual operation of the station indicates that each performance index of ZZX30 runner modified meets the requirement. And ZZX30 has high efficiency and output stability, as well as better overall performance than before. The power station has obtained good economic efficiency, and it also shows the effectiveness of the methods of modification design and performance estimate used in this paper.更多还原