【作者】 张双全；

【导师】 吴克启； 韦彩新；

【作者基本信息】 华中科技大学 ， 流体机械及工程， 2008， 博士

【摘要】 随着水电机组单机容量的提高,机组尺寸的逐步增大,比转速的不断提高,相对刚度的减弱,人们对于大型混流式水轮机的运行稳定性日益重视,同时,随着技术的高速发展,机组运行的自动化程度越来越高,无人值班、少人值守,远程控制的水电厂日益增多,对机组运行稳定性的要求亦日趋严格。另一方面,国内外许多大型混流式水轮发电机组相继出现振动问题,不仅影响了正常的生产运行,有的还危及到机组的安全,因此,水力稳定性已经引起电力及制造行业的普遍关注,也给行业内的专家学者提出了新的研究课题,本文的研究就是基于这样的背景下进行的。大型混流式水轮机水力稳定性有关的原因比较复杂,在电站的表现形式也多种多样,如尾水管低频压力脉动、卡门涡、叶道涡等,在这些水力原因中,尾水管涡带又是机组振动最主要的原因,其危害性也最大。而对水力稳定性的研究方法主要有模型试验研究、真机试验研究、CFD数值解析这三种。本文针对东江水电厂机组出现的振动问题,采用以上三种方法相结合的手段,对机组振动的原因进行了综合研究。水轮机模型试验是研究真机水力稳定性的重要手段。尽管现在已经具备对水轮机进行较准确的数值模拟及性能预测的手段及仿真技术,但是最终仍需进行模型试验来确定模型转轮的能量特性、汽蚀特性以及水力稳定性等。对于已运行的机组,通过模型试验可以模拟电厂的运行工况以研究真机运行的各种特性。通过对电厂的模型机组进行多方面试验研究的结果表明,转轮的能量特性较差;在小开度下,模型机组尾水管内存在较大的低频压力脉动;不同形状的泄水锥对模型机组尾水管的低频压力脉动有较大的影响;针对具体情况,采用不同的补气方法可减轻机组的振动。真机试验是研究真机水力稳定性的直接手段,模型试验固然重要,但也有其局限性,如真机与模型几何相似的假定条件就是相对的,加上水轮机过流部件内的流动极为复杂,各电站水轮机结构的设计也差别很大,由水轮机模型试验的振动特性很难预估真机的运行稳定性,使水轮机振动的真机试验研究为国内外专家所重视。通过大量的研究表明,水轮机振动有其共性,也有其个性。可见,通过模型试验并不能全面了解真机的所有性能,尤其是和机组振动密切相关的动态特性,因此,虽然相比模型试验来说,真机试验受到许多实际条件的限制,但是在研究具体电站的具体问题,特别是要了解机组的制造质量、安装质量等模型上没有的信息对机组运行稳定性的影响时,真机试验必不可少。本论文对电厂的真机做了多方面的试验研究,包括过流部件的实测;不同水头下的变负荷、变励磁试验研究;机组振动的频率特性分析;补气对真机稳定性的影响以及机组振动与大坝振动的之间的关系分析。试验的结果表明,东江水电厂机组的制造及安装质量存在较大的缺陷;机组在每个水头下均存在两个振动工况区,且随着水头的升高,振动工况区有向小出力偏移的趋势;在部分负荷时,尾水管中产生偏心涡,引起尾水管低频压力脉动;采用合适的补气方法及补气量,对于减轻东江水电厂机组的振动是有效的。与模型试验和真机试验相比,CFD数值解析在成本与周期、所获得的信息量等方面有着巨大的优势,因此,这一方法的应用也越来越普遍、深入,也使得人们对于大型混流式水轮机过流部件中主流内特性的了解日益加深。本文通过“部分耦合”的方法对真机在不同运行工况下的稳定场进行了数值解析,并全面的分析了各过流部件内的流动特性以及其能量特性。仅仅对机组的过流部件进行稳定场的CFD数值分析还不足以解决所有与水轮机水力稳定性有关的问题,因此在本论文的最后,采用雷诺应力湍流模型对真机尾水管在不同运行工况下进行了非稳定场的CFD数值解析,分析涡带的运动规律及其产生的低频压力脉动特性,并与真机的试验结果进行了比较,结果比较吻合。更多还原

【Abstract】 Along with the increase of the unit installed capacity, the unit size, the specific speed and the weaken of the relative rigidity of hydraulic power unit, the operating stability of large-scale Francis turbine received much more attention increasingly. Meanwhile, the rapid development of technology makes the automaticity of unit operation more and more higher and appears a large amount of hydropower stations with nobody or a few on duty, remote control, so the requirement of the unit operating stability becomes strict increasingly. On the other hand, there come forth vibration problems in many large-scale Francis turbines at home and abroad, which influence the normal operation not only, some of them endanger the units but also, therefore, the hydraulic stability has brought more attention in trades of electricity and manufacturing, the new research field has been brought about to the professionals and scholars also. This paper’s research is based on the background.The concerned reasons about the hydraulic stability in large-scale hydropower unit are complicated and the phenomenon are varied, such as the low-frequency pressure pulsation in draft tube, the Karman vortex and the vortex between blades etc. In which of these, the draft tube vortex is the primary reason to bring about the unit vibration. The research methods of hydraulic stability are mainly model test, field test and CFD numerical simulation. Aiming at the vibration problem appeared in DongJiang hydropower unit, this paper comprehensively analyzed the reasons applying the combination of above three methods.The model test of hydraulic turbine is the very important way to study the prototype’s hydraulic stability. Although there can be provided the means and simulation technologies now to give the relatively accurate numerical simulation and the performance prediction of hydraulic turbines, finally the model test is required to determine the energy performance, cavitation performance as well as hydraulic stability of model runner. As to the units in use, it can research the prototype’s operating performance by means of model test to simulate the operating condition of units. The results of model test in many aspects indicate that the energy performance of the runner is relatively low; in small opening condition, there exist low-frequency pressure pulsation in draft tube; the draft cone with different configuration has great influence with the low-frequency pressure pulsation in draft tube; the application of different supplying air method can abate the vibration of the units.The field test is the direct way to research the prototype’s hydraulic stability. The model test is very important but with limitations, for example, the assumption condition of the geometric similarity between model and prototype is relatively, meanwhile, the flow in passing components of hydraulic turbine is very complicated, the structural design difference among the hydraulic turbines is great and it’s difficult to predict the prototype’s operating stability from the vibration performance of the model, all of those make the research of field test received more attention for professionals. Many results of research indicate that the characteristics of hydraulic units’vibration have not only commonness but also individuality. Obviously, it is impossible to reveal the prototype’s general performance by means of model test especially the transient performance related to the unit vibration. Thus, although the field test has many limitations comparing with model test, but it is necessary in order to research the specific problem especially to find out the influence to unit operating stability of the manufacturing and installation quality without in model test information. The paper carried out many field test research including the passing components measurement, the test of load variation and excitation variation with different head, the frequency characteristic analysis of unit vibration, the influence supplying air to prototype’s stability and the analysis of the relationship between unit vibration and dam vibration. The results indicate that there exist important objections in manufacturing and installation quality of DongJiang units, the units have two vibration region in different head, which has the tendency to offset to lower load with the increase of head, under part-load conditions, it brings about eccentric vortex in draft tube, which causes the low-frequency pressure pulsation, it is available to abate the vibration of DongJian units by means of suitable method and quantity of supplying air.The CFD numerical simulation has great advantageous in cost, periods and information content comparing with the model test and field test, so this method becomes more and more popular and ingoing, it also makes the main flow performance in large-scale Francis turbines clear increasingly. The paper numerically simulated the prototype’s stable flow field in different operating conditions by means of partly coupling method and generally analyzed the flow and energy performance in passing components.It is not enough to resolve all of the problems related to the hydraulic stability only to analyze the stable field in passing components. Finally, the paper numerically simulated the transient field in prototype’s draft tube under different operating conditions by means of Reynolds stress turbulence model and analyzed the law of motion of vortex rope as well as the performance of low-frequency pressure pulsation and compared with field test results.更多还原