大型水库化学污染对水力机组空化性能的不利影响

发布时间：2018-08-13 14:23

【摘要】：水能资源是我国能源结构的重要组成部分,随着我国西南一大批巨型水电站规划上马和南水北调工程许多大型泵站相继建成,大型水利工程中水力机组运行的安全性和稳定性显得尤为重要。而水力机械具有良好的的空化性能是保证整个水利水电工程与机组安全可靠运行的关键因素之一。在我国水利水电工程大规模建设的同时,一个不容忽视的问题是目前我国诸多河流与湖库面临着严峻的水污染形势,水体富营养化严重,主要污染物为总磷、总氮和重金属络合物等。此前,水力机械的设计、试验、模拟等大多以清水为基础进行。当引用水质遭受化学污染性质发生变化时,对水力机械的空化性能是否造成影响和造成何种影响是一个亟待研究的问题。本文重点就以遭受严重总磷污染的乌江流域内的电站为例,研究总磷污染水体的空化压力特性以及对水轮机空化性能的影响,并将试验结果运用到空化流的数值模拟中去,取得较好的效果。为了了解乌江流域的总磷污染形势,实地采样考察了流域中、下游梯级电站引用水的总磷含量和底泥情况,并对流域内主要支流的污染情况作了资料收集和取样化验。化验结果表明：乌江流域中、下游总磷污染严重,水质为劣V类,底泥重金属含量高。为了研究化学污染的水对水力机械空化性能的影响,在射流试验装置中对比了引用水质为磷石膏悬浊液和清水时空化初生的条件和空化发展的状态,高速摄影观察到射流装置内引用水为总磷悬浊液时更容易发生初生空化,相同工况下空化发展更为强烈,空泡云体积明显变大。同时对总磷污染水的空化压力特性进行了专项实测,表明水体的初生空化压力与临界空化压力较清水时压力值明显增大,且在饱和浓度内,空化压力值随着总磷浓度的提高而增大。长期以来,许多水力机械书籍以及论述空化与空蚀的文献中,都将空化与水的汽化混为一谈,将发生空化时的水压认定为当时温度下水的汽化压力或饱和蒸汽压力,并将该压力值应用到水力机械的空化计算中。根据以上试验结果,考虑水质因素对描述水力机械空化性能的主要参数如空化数、水轮机空化系数、水轮机吸出高度等值做了必要的修正,并应用修正值对遭受总磷污染的构皮滩电站和三峡电站的空化性能做了评价分析。绕流物体如水轮机与叶片泵转轮叶片,当沿流面所截的翼型吸力面发生空化且来流冲角不大时,便可形成犹如附着在固体表面上的空穴。通过试验观察空化发生时空泡的变化过程,得到了空化压力与单位体积内空泡的数量和直径的关系。实验证实,空穴内部为含有很多空泡的混合水体,而不是以往普遍认为的气体,空穴的形状和尺寸同空穴内部的空泡尺寸与数量直接相关,空泡的尺寸与数量则由引用水的空化压力特性和吸力面压力分布决定,将引用水空化压力特性与三维湍流数值模拟结合起来模拟了叶轮内部的空化流动,与实际情况相符。
[Abstract]:Hydropower resources are an important part of China's energy structure. As a large number of large-scale hydropower stations in southwest China have been planned and many large-scale pumping stations have been built in succession for the South-to-North Water Transfer Project, the safety and stability of the operation of hydraulic units in large-scale water conservancy projects are particularly important. One of the key factors for the safe and reliable operation of the whole water conservancy and hydropower project is the large-scale construction of the water conservancy and hydropower project in China. At present, many rivers and lakes in China are facing severe water pollution situation. The eutrophication of the water body is serious. The main pollutants are total phosphorus, total nitrogen and heavy metal complexes. Previously, the design, test and Simulation of hydraulic machinery were mostly based on clean water. Whether or not the cavitation performance of hydraulic machinery will be affected and what kind of influence will be caused when the quality of water quoted is changed by chemical pollution is an urgent problem to be studied. In order to understand the situation of total phosphorus pollution in the Wujiang River basin, the total phosphorus content in the water of cascade hydropower stations in the middle and lower reaches of the basin was investigated by field sampling. The results show that the total phosphorus pollution is serious in the middle and lower reaches of Wujiang River basin, the water quality is inferior V and the content of heavy metals in the sediment is high. The water quality is phosphogypsum suspension and clean water, and the condition of cavitation development. High-speed photography shows that when the water is the total phosphorus suspension, the primary cavitation is more likely to occur, the cavitation development is more intense and the volume of cavitation cloud is obviously larger. The special measurement shows that the primary and critical cavitation pressures of water body are obviously higher than those of clean water, and the cavitation pressure increases with the increase of total phosphorus concentration in saturated concentration. The water pressure at the time of cavitation is defined as the vaporization pressure or saturated vapor pressure of the water at the temperature at that time and applied to the cavitation calculation of hydraulic machinery. The cavitation performance of Goupitan Hydropower Station and Three Gorges Hydropower Station polluted by total phosphorus is evaluated and analyzed. When the suction surface of the airfoil intercepted along the flow surface is cavitated and the inflow angle is small, the flow around the object such as the turbine and the blade pump runner blade can be formed as if it is attached to the solid surface. Cavitation. The relationship between cavitation pressure and the number and diameter of cavitation in a unit volume is obtained by observing the process of cavitation. It is confirmed by experiments that the cavitation is a mixture of water with many cavitations, rather than the gas generally believed in the past. The cavitation pressure and suction surface pressure distribution determine the size and quantity of the cavitation. The cavitation flow in the impeller is simulated by combining the cavitation pressure characteristics of the water and the three-dimensional turbulent numerical simulation.
【学位授予单位】：中国农业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：X524;TV136

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