基于数值模拟的水轮机增容改造研究

发布时间：2018-05-28 17:54

本文选题：混流式水轮机 + 增容改造　；参考：《兰州理工大学》2017年硕士论文

【摘要】：对已建具有增容潜力的水电站机组更新改造,成本小、收效快,社会经济效益可观。运行多年的部分中小型电站普遍存在着技术指标落后、制造质量差、过流部件磨损严重、设备年久失修、发电量逐年减少等问题,不仅浪费大量的水力资源,而且影响着电站的安全运行。目前CFD技术发展迅速,成果显著,达到了工程应用水平。探究如何应用CFD这一先进工具对老旧电站的水轮机进行增容改造具有重大现实意义。本文针对青海古浪堤水电站HL741-WJ-84水轮机在实际运行中出现的问题,“量体裁衣”式制定增容改造方案。首先对比分析诸多较优模型转轮,初步选取目标转轮;然后根据水轮机既定通流部件的几何约束条件对所选目标转轮进行一定改型,使转轮既保持本身优良性能又满足电站改造要求。鉴于小型卧式水轮机在汛期运行时出现转轮被杂物频繁堵塞而影响正常发电的情形,从增加水轮机出力与过流能力的角度出发,采用在改型转轮基础上减少三个叶片后制造新转轮的方案对原水轮机增容改造。以CFD为基础探究可用于水轮机实际改造的数值计算及水力性能估测方法,对改造结果进行数值验证并分析水流流态是否均匀合理以达到定性指导和评价改造方案的目的。本文基于流场数值计算,分析水轮机增容改造前后的流场,预估机组的整体性能。通过求解Reynolds时均N-S方程,在FLUENT中选取标准κ-ε湍流模型并采用SIMPLE算法,对改造前后的水轮机全流道进行流场计算,模拟改造前后的水轮机在四个典型工况下运行时的流动状况,求得各个工况下水轮机整体及各通流部件内的流动信息,获得改造前后水轮机水动力学的特性差异,给出了水轮机更换转轮改造后效率和出力随导叶开度变化的规律。改造后水轮机整体流动均匀、流态分布合理,几乎不存在流场的扰动。蜗壳中水流流动平稳顺畅,过流能力增强,不存在压力与速度突变等不稳定现象;叶片的数值计算结果表明,减少叶片数对叶片背面压力分布影响较大,转轮在各工况下运行时因叶片背面负压产生的翼型空蚀较原HL741转轮有所改善,但叶片背面靠近下环处进口段极小区域存在空蚀性能恶化的现象,为安全起见可对该区域采取一定的抗空蚀措施;尾水管在原最优工况与较大开度之间的流动状况均匀稳定,偏心涡带减弱,整体流线顺畅,流动性能、水力性能等要优于改造前;改造后水轮机最优工况点偏向大流量区,机组增容幅度可达13%,效率达到91%。本文所得结果可用于HL741-WJ-84水轮机的实际改造并指导电站的运行。
[Abstract]:The cost is small, the effect is fast and the social economic benefit is considerable. Some small and medium-sized power stations which have been running for many years have some problems, such as backward technical indexes, poor manufacturing quality, serious wear and tear of overcurrent parts, old equipment disrepair and decreasing power generation year by year, which not only waste a large number of hydraulic resources, but also reduce the power generation year by year. It also affects the safe operation of the power station. At present, the CFD technology develops rapidly, the achievement is remarkable, has reached the engineering application level. It is of great practical significance to explore how to apply CFD, an advanced tool, to the retrofit of hydraulic turbines in old power stations. Aiming at the problems of HL741-WJ-84 turbine in practical operation of Gulangdi Hydropower Station in Qinghai Province, this paper formulates the scheme of capacity increase and retrofit. Firstly, many better model runner are compared and analyzed, then the target runner is selected preliminarily, and then the selected target runner is modified according to the geometry constraint condition of the given flow passage part of the turbine. The runner can not only maintain its own excellent performance but also meet the requirements of power plant transformation. In view of the fact that the runner of a small horizontal turbine is clogged frequently by sundries during flood season, which affects the normal power generation, this paper starts from the point of view of increasing the outputting force and overcurrent capacity of the turbine. The new runner after reducing three blades on the basis of the modified runner is adopted to increase the capacity of the original turbine. Based on CFD, this paper explores the numerical calculation and hydraulic performance estimation method which can be used in the actual retrofit of hydraulic turbines, and verifies the results of the revamping and analyzes whether the water flow pattern is even and reasonable in order to achieve the purpose of qualitatively guiding and evaluating the retrofit scheme. Based on the numerical calculation of the flow field, the flow field before and after the retrofitting of the turbine is analyzed, and the overall performance of the turbine is predicted. By solving the average N-S equation of Reynolds, selecting the standard 魏-蔚 turbulence model in FLUENT and using the SIMPLE algorithm, the flow field of the turbine before and after the revamping is calculated, and the flow state of the turbine before and after the revamping is simulated under four typical operating conditions. The flow information of the whole turbine and the flow passage parts are obtained, and the differences of hydrodynamic characteristics of the turbine before and after the revamping are obtained. The law of the change of the efficiency and the output force with the guide vane opening after the revamping of the turbine runner is given. After the revamping, the whole flow of the turbine is uniform, the flow distribution is reasonable, and there is almost no disturbance of the flow field. In volute case, the flow of water is smooth and smooth, the capacity of overcurrent is enhanced, and there is no unstable phenomenon such as sudden change of pressure and velocity, and the numerical calculation results of blade show that reducing the number of blades has a great influence on the distribution of pressure on the back of blade. The cavitation erosion of the airfoil caused by the negative pressure on the back of the blade is better than that of the original HL741 runner when the runner is running under various operating conditions, but the cavitation erosion performance is deteriorated in the very small area near the inlet of the lower ring on the back of the blade. For the sake of safety, some anti-cavitation measures can be taken in this area; the flow condition of draft tube is uniform and stable between the original optimum working condition and the larger opening, the eccentric vortex belt is weakened, the whole flow line is smooth, and the fluidity is very good. The hydraulic performance of the turbine is better than that of before the retrofit, the optimum operating point of the turbine deviates to the large flow zone after the revamping, the capacity increase range of the unit can reach 13%, and the efficiency reaches 91%. The results obtained in this paper can be applied to the practical transformation of HL741-WJ-84 turbines and guide the operation of power stations.
【学位授予单位】：兰州理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TV738

【参考文献】