共查询到19条相似文献,搜索用时 250 毫秒
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在水库开闸泻水过程中,高速水流掺气以及消能过程中水流的强烈碰撞会卷吸大量气体形成溶解气体过饱和现象,进而引起鱼类患气泡病死亡。此文引入气体向气泡界面和水体表面传质的机理,利用坐标变换对自由水表面边界进行特殊处理,在三维紊流两相流模型的基础上模拟气泡在水中的运动和溶解,从而计算过饱和气体的浓度分布,并将此模型运用在对葛洲坝饱和气体模拟预测中,还和实测值进行了比较。结果表明:运用坐标变换方法后的模型能更准确地模拟饱和气体浓度。 相似文献
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紊动水体表面传质系数的实验研究 总被引:4,自引:1,他引:4
本文根据紊动扩散理论及气液界面质量传递过程,提出了紊动水体复氧过程的概化模型。在对紊动水体复氧过程的研究中,采用了将由分子扩散引起的氧传递和由紊动扩散引起的氧传递分别进行研究的新方法。根据在紊动诱发实验装置内进行的大量复氧实验及理论分析,分别确定了无紊动和不同紊动强度下的表面传质系数,并建立了表面传质系数与紊动动能之间的定量关系式。这一关系充分考虑了表面紊动动能对复氧的影响,对于研究紊动复氧水体表面传质系数、复氧过程及水体内溶解氧浓度的分布具有重要意义。 相似文献
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典型盐碱地改良区农田排水沟水体与底泥界面氧通量研究 总被引:2,自引:0,他引:2
农田排水沟水体与底泥中的氧含量决定了底泥中各种生源要素的最终归趋,对维持农田排水沟的水环境至关重要。本论文以陕西富平县卤泊滩盐碱地改良区农田排水沟水体与底泥为研究对象,从环境微界面角度出发,根据多年监测数据构建室内试验,采用高分辨率微环境固液剖面传感系统(丹麦Unisense微电极系统),探究了研究区农田排水沟水体与底泥界面氧通量变化规律。研究结果表明:底泥中的溶解氧随深度的增加逐渐减小,直至溶解氧浓度为零,到达厌氧层;溶解氧剖面浓度的实测值与Profile模型模拟值的相关系数均在0.995以上,表明该模型能客观地描述溶解氧在农田排水沟水体与底泥扩散边界层和底泥中的分布;农田排水沟上游不同监测点位的底泥含氧层厚度在3.5~6 mm之间,而下游监测点位的底泥含氧层厚度约为1.5 mm,差异显著;通过氧浓度线性分布、剖面拐点法得到氧气扩散边界厚度,上游监测点位的氧气扩散边界层厚度基本在1 mm,而下游监测点位的氧气扩散边界层厚度减少至0.2 mm。农田排水沟水体与底泥界面氧通量的测定,对于认识农田排水沟底泥的地球化学过程及水环境作用机理具有重要意义,可为农田排水沟水环境治理提供参考依据。 相似文献
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采用现场调查和室内实验相结合的方法研究了黄河小浪底水库排沙期间下游河流出现鱼类死亡现象的原因。2010年度小浪底水库排沙期间,下游出现了高含沙水流过程,伴随出现了鱼类死亡现象,调查发现受影响鱼类有5目5科11种。水库排沙期间的含沙量、溶解氧变化过程的现场调查及室内实验结果表明,小浪底水库排沙时细颗粒泥沙含量较高,堵塞和损坏鱼鳃是导致鱼类死亡的原因之一。当含沙量大于80 kg/m3时,水体溶解氧下降至鱼类生存所需下限2mg/L以下,鱼类在短时间内缺氧而死亡;当含沙量低于60kg/m3时,根据现场调查结果及相关人员经验判断水库下游河道内不会出现鱼类死亡漂移现象。水库排沙期间,下游河道水体的含沙量与溶解氧浓度具有较好的相关性,即河道水体的溶解氧浓度随着含沙量的增加而减少,可通过控制出库含沙量及其持续时间减轻对鱼类的影响。 相似文献
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小浪底水库排沙对下游鱼类的影响研究 总被引:2,自引:0,他引:2
采用现场调查和室内实验相结合的方法研究了黄河小浪底水库排沙期间下游河流出现鱼类死亡现象的原因。2010年度小浪底水库排沙期间,下游出现了高含沙水流过程,伴随出现了鱼类死亡现象,调查发现受影响鱼类有5目5科11种。水库排沙期间的含沙量、溶解氧变化过程的现场调查及室内实验结果表明,小浪底水库排沙时细颗粒泥沙含量较高,堵塞和损坏鱼鳃是导致鱼类死亡的原因之一。当含沙量大于80kg/m3时,水体溶解氧下降至鱼类生存所需下限2mg/L以下,鱼类在短时间内缺氧而死亡;当含沙量低于60kg/m3时,根据现场调查结果及相关人员经验判断水库下游河道内不会出现鱼类死亡漂移现象。水库排沙期间,下游河道水体的含沙量与溶解氧浓度具有较好的相关性,即河道水体的溶解氧浓度随着含沙量的增加而减少,可通过控制出库含沙量及其持续时间减轻水库排沙对鱼类的影响。 相似文献
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射流卷气入水产生气泡群的湍流流动常见于水面船周边,是一种复杂多尺度气液两相湍流流动.为把握这一流动的时空演化规律,在带有自由液面的循环水槽中搭建了实验装置,使用光纤气泡探针对不同参数下的卷气泡状流动进行了实验测量.通过测量得到了流动中时均的体积分数分布、气泡速度以及气泡尺寸.还使用水听器对射流卷气入水产生气泡群的湍流流... 相似文献
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通过对虹吸式输水管道输水能力的试验研究,观测到不同安装高度下的气液两相流现象。量测了不同安装高度相应水位差下的流量的大小,并分析了流量变化规律。研究发现,随着安装高度的增大,虹吸管内气液两相流流型由气泡流转化为气团流。分析原因发现在安装高度h_s=2 m时,流量减小率与面积减小率相等,表明气液两相流时过流面积小于液相满流时过流面积是流量的减小的主要原因;当安装高度h_s2 m时,流量减小率与面积减小率相差较大,表明流量的减小不仅与面积变化有关,还应与沿程阻力系数有关。掺气浓度的增大使管内压降增大,压降的增大导致了管内阻力增大,从而使沿程阻力系数增大,而导致流量减小。 相似文献
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刘继广 《中国水利水电科学研究院学报》2007,5(2):81-86,94
从气体运动状态方程出发,研究了竖井有压流动模型中气水两相流的运动规律,分析了气泡几何相似、运动相似以及动力相似的条件,指出掺气浓度相似律是研究气水两相流相似问题的又一必要条件,即原、模型的掺气浓度必须相等,前提为大气压强或密度相似。对照公伯峡水电站竖井水平旋流洞原型与常压模型水流中掺气浓度测值的差异,给出了该竖井流态、压强、流量等不相似现象的合理性解释。依据掺气浓度相似律准则进行气水两相流模拟研究,对于发展传统水力学研究理论、创新研究方法、完善工程应用技术等,可以起到有效的推动作用。 相似文献
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A high concentration of the total dissolved gas(TDG) in a flow downstream high dams may cause the gas bubble disease in fishes.To better understand the spatial distribution of a supersaturated TDG,a numerical simulation approach for determining the TDG concentration is shown to be effective and convenient; however,the determination of the model parameters relies to a great extent on the observed field data,which are scarce but are very sensitive to the accuracy of the simulation.In this regard,determining the source parameter in the TDG transport equation is the primary concern of this paper.Observed field data from six different spillways in China are used to calibrate the source parameter.A relationship between the source parameter and the hydrodynamic characteristics is established.The inclusion of this relationship in the predictive relationship will enable an accurate and rapid estimation of the source parameter and may help in developing mitigation measures for the TDG supersaturation downstream the spillways. 相似文献
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SIMULATIONS OF THE THREE-DIMENSIONAL TOTAL DISSOLVED GAS SATURATION DOWNSTREAM OF SPILLWAYS UNDER UNSTEADY CONDITIONS 总被引:1,自引:0,他引:1
Dams are often operated in a way to discharge over the spillways, which would cause a high dissolved concentration of air and be harmful to fish. The bubble transfer and the water surface transfer play an important role in affecting the concentration of the Total Dissolved Gas (TDG). Based on recent numerical simulations of the total dissolved gas saturation, in this article, a two-phase TDG transport equation is adopted to develop an unsteady three-dimensional (3-D) two-phase flow Computational Fluid Dynamics (CFD) model, including a number of parameters such as water depth, pressure and air volume entrained. This model is used to predict the hydrodynamics and the TDG distribution under unsteady discharge conditions. Good agreement between measured and numerical results is obtained for a case study. 相似文献
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Elevated levels of the Total Dissolved Gas (TDG) may be reached downstream of dams, leading to increased incidences of gas bubble diseases in fish. The supersaturated TDG dissipates and transports more slowly in reservoirs than in natural rivers because of the greater depth and the lower turbulence, which endangers the fish more seriously. With consideration of the topographical characteristics of a deep reservoir, a laterally averaged two-dimensional unsteady TDG model for deep reservoir is proposed. The dissipation process of the TDG inside the waterbody and the mass transfer through the free surface are separately modeled with different functions in the model. Hydrodynamics equations are solved coupling with those of water temperature and density. The TDG concentration is calculated based on the density current field. A good agreement is found in the simulation of the Dachaoshan Reservoir between the simulation results and the field data of the hydrodynamics parameters and the TDG distribution in the vertical direction and their unsteady evolution with time. The hydrodynamics parameters, the temperature and the TDG concentration are analyzed based on the simulation results. This study demonstrates that the model can be used to predict the evolutions of hydrodynamics parameters, the temperature and the TDG distribution in a deep reservoir with unsteady inflow and outflow. The results can be used in the study of the mitigation measures of the supersaturated TDG. 相似文献
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重点研究了南水北调引江济汉工程后三峡水库运用50年内,不同取水口河段泥沙冲淤、河势、水位的变化趋势,为合理选择进水口提供了科学依据。研究成果表明,由于三峡水库的拦沙及调节作用,改变了下游河道的来水来沙条件,使下游河段冲淤发生变化,河床处在不断调整过程中。在三峡水库运用50年内,各取水口河段河床冲刷主要集中在前10年,随后出现冲淤平衡、淤积等。兴建取水口工程后,工程对河段上、下游的影响是有限的,但其影响仅限于工程附近;各取水口的取水条件,均呈现出随着三峡水库运用年限的增加而发生变化。 相似文献
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鄱阳湖与长江关系及三峡蓄水的影响 总被引:12,自引:2,他引:10
通过机理研究,结合实测资料分析,说明了鄱阳湖河相与湖相的分界水位,阐明了长江干流来流对湖口出流的顶托作用,并给出了湖口出现倒流的条件,得到了鄱阳湖对洪水的调节作用系数,初步理清了鄱阳湖与长江干流江湖相互影响规律。分析了三峡水库蓄水期的影响及鄱阳湖的枯水特性。三峡水库运用初期,其蓄水的前半段时间,鄱阳湖向长江干流多补水量23亿m3,后半段少补水量11亿m3。三峡水库运用30年后,在河道冲刷、可补水量减少和蓄水的共同作用下,鄱阳湖的枯水季节相当于提前了1个月左右。本研究对认识江湖关系及鄱阳湖治理具有重要意义。 相似文献
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Shudan Xue Li Kefeng Ruifeng Liang Lu Cao Yuanming Wang Yong Li Jingjie Feng 《河流研究与利用》2019,35(9):1511-1519
Total dissolved gas (TDG) supersaturation in the upper Yangtze River caused by high spill rates upstream of hydroelectric dams has become a serious environmental problem in recent years. TDG supersaturation downstream of the Xiangjiaba Dam was investigated during flood periods in 2014 and 2015. Alongside this, an in situ study was conducted to evaluate the impacts of TDG supersaturation on grass carp (Ctenopharyngodon idellus) and rock carp (Procypris rabaudi). TDG supersaturation levels ranged from 115% to 131% in 2014 and from 118% to 128% in 2015. During 2014, TDG supersaturation first decreased and then increased and finally remained relatively stable. In contrast, the TDG supersaturation level remained between 122–126% for a relatively long time in the 2015 study period. During 2014, grass carp confined to water depths of 0–1 and 1–2 m began to die after 45 hr of exposure, and most grass carp died between 90 and 130 hr when TDG supersaturation level was greater than 127%. The first observed death during 2015 occurred after 30‐hr exposure. The survival of rock carp was greater than 50% when they were restricted to water depths of 0–1 m. Only three rock carp died when they were confined to water depths of 0–2 m, and no dead fish were recorded at water depths of 0–3 m. 相似文献