高速掺气水流数值模拟研究

应用FLUENT商用软件及其二次开发技术,采用双流体模型及混合k-ε 湍流模型对带有掺气挑坎的陡槽高速掺气水流进行了二维数值模拟。根据掺气水流的特点,重点对相间阻力模型进行了改进,特别在构建相间阻力本构关系式时考虑了湍流扩散的影响。计算结果表明,在相间阻力模型中考虑湍流扩散的影响,可明显改善以往数值计算对水流掺气估算不足的状况,使掺气浓度的分布和掺气量的计算结果与试验数据符合更加良好。说明在合理构建相间相互作用力的基础上,采用双流体模型可较好地模拟高速水流掺气现象。     

挑坎下游高速掺气水流的数值模拟

应用FLUENT软件及其二次开发技术,采用双流体模型及混合k-ε湍流模型对带有掺气挑坎的陡槽高速掺气水流进行了二维数值模拟。根据掺气水流的特点,重点对相间阻力模型进行了改进,特别在构建相间阻力本构关系式时考虑了湍流扩散的影响。计算结果表明,在相间阻力模型中考虑湍流扩散的影响,可明显改善以往数值计算对水流掺气估算偏低的状况,使掺气浓度的分布和掺气量的计算结果与试验数据符合更加良好,说明湍流扩散对掺气浓度的分布有重要作用。当采用双流体模型模拟掺气水流时,相间作用力模型应考虑湍流扩散的影响。     

掺气水流相间作用力模型分析

本文分析了掺气水流内部结构形态及水、气两相间速度滑移的特征，得到如下结论：在掺气水流中，宏观的相间速度滑移不会很大；水、气两相间动量的传递以惯性推动作用为主，并给出了虚质量力的具体表达式。     

基于数值模拟的若坑水库溢洪道水力特性分析

为探究若坑水库溢洪道建筑物三维流场模拟及水力特性,应用数值模拟技术对溢洪道掺气坎周围掺气和水流特征展开模拟分析,得出泄流场、压力场、流速场、水面线等水力学参数分布趋势特征,进而对溢洪道通气孔处通气量和风速以及跌坎掺气水流运行特征展开模拟分析。结果表明,不同特征直径气泡对通气量存在较大影响,但整体而言,模拟值均超出设计值;水体中部掺气浓度沿程表现出衰减趋势,空腔负压模拟值明显大于设计值,不利于掺气空腔的完整;尾坎消能工边长的增大能较好消耗水流势能并减小负压空腔,但同时会引起非稳定流速,故应将尾坎边长控制在合理范围内。     

泄槽底部掺气坎后水流掺气浓度分布模型试验

针对泄槽底部掺气坎后的掺气浓度分布规律较为复杂、研究成果较少的问题,为了更清楚地探究泄槽底部掺气坎后上游直段、反弧段及下游直段水流掺气浓度分布规律,采用含有反弧段的泄槽进行模型试验研究。试验结果表明:上游直段、反弧段及下游直段水流中不同水深处掺气浓度的沿程变化规律是不相同的;其他条件不变时,水流掺气浓度随掺气坎高度的增加而增大,随反弧段反弧半径的减小而减小;掺气坎高度和反弧半径对掺气设施的有效保护范围有一定的影响,适当提高掺气坎的高度和反弧段的半径对增大掺气设施的有效保护长度有利。     

明流泄洪隧洞中自掺气水流浓度分布及其计算

通过对明渠和明流隧洞中自掺气水流的对比试验，研究了明流隧洞中洞顶的存在对掺气浓度分布的影响。试验结果表明：洞顶的存在可导致洞顶附近掺气浓度分布随高度的增加而减小的情况，同时，在水点跃移区的中上部高含气段，掺气浓度亦有所减小，甚至全断面掺气浓度均低于99%.根据有无顶盖时水点通量守恒的条件，建立了一个计算明流泄洪隧洞中自掺气水流掺气浓度分布的理论公式，并在适当的假设前提下，对公式作了简化并对洞高分别为9cm和10cm情况下，不同流量、不同余幅的掺气浓度进行了计算，计算结果与试验资料吻合较好。     

突扩式跌坎消力池掺气特性试验

采用模型试验对突扩式跌坎消力池内水流的掺气浓度进行了量测,研究了来流条件、突扩比、水流流态对掺气特性的影响。结果表明：突扩式跌坎消力池掺气水流典型流态为水跃流叠加在射流之上,跃首被射流分裂成两部分,气泡跃移区在泄槽延长线范围内,长度较无突扩跌坎消力池有所减小,气泡悬移区长度有所增加,临底长度有所减小,突扩处为清水回流区,携带部分气泡;无突扩跌坎消力池底板掺气浓度呈降峰形曲线分布,各纵向断面沿程掺气浓度分布均匀;突扩式跌坎消力池底板掺气浓度呈升峰形曲线分布,掺气浓度在消力池底板1/4中线处最大,1/2中线处次之,靠近边墙处最小;在同一水力条件下,突扩式跌坎消力池底板掺气浓度较无突扩跌坎消力池有显著降低,且消力池底板掺气浓度不随突扩比的增大而减小。     

水垫塘不同水流结构区掺气浓度分布规律试验研究

为了得到水垫塘局部掺气浓度分布规律,减少过流边壁空蚀破坏的发生,采用水力学模型试验的方法,将水垫塘内水体进行水流结构分区,通过改变泄流流量、水流入射角度、水垫深度三个条件,实测水垫塘不同水流结构区掺气浓度值,研究气体在不同水流结构区的运动机理。对试验所测数据进行整理得到水垫塘不同水流结构区掺气浓度分布曲线,且不同的水力条件与其拟合近似为二次曲线关系。通过分析得到水垫塘不同水流结构区掺气浓度分布规律如下:各水流结构区掺气浓度随泄流流量增大而增大;射流与附壁射流区紊动掺混随泄流流量增大而更加剧烈;掺气浓度随水垫深度增大而减小;淹没射流区与旋滚区掺气浓度随水流入射角度增大而减小,附壁射流区掺气浓度随入射角度增大而增大,但变化不明显。     

明流脉动压强特性对自掺气发展影响试验研究

通过系列模型试验,采用脉动压强仪和针式掺气浓度仪,在不同初始流速与水深条件下详细测量了陡槽自掺气水流沿程各断面掺气浓度与脉动压强,重点分析了脉动压强与掺气浓度分布之间的相关关系,以及断面平均脉动强度对掺气区气泡扩散的影响。试验结果表明:随着明渠水流自掺气沿程不断发展,同一个断面上的脉动压强从断面底部至自由面呈现出先增大后减小的趋势,其中最大值位于断面掺气扩散区;断面平均脉动强度呈现沿程逐渐增大的变化趋势;在不同来流流速、水深及雷诺数条件下,自掺气水流断面平均脉动强度与断面掺气扩散区域之间呈现良好的相关关系。     

前置掺气坎坡度对阶梯溢洪道掺气水流影响的数值模拟

为研究复杂边界条件下气液两相界面的流动及混掺现象对工程建设的影响,结合某大型水电站的溢洪道,利用RNG k-ε模型对其进行三维流场模拟,采用有限体积法离散控制方程,并用GMRES算法进行压力求解,对前置掺气坎式阶梯溢洪道和传统阶梯溢洪道泄流壁面上的高速掺气水流进行数值模拟。结果表明:随着掺气坎坡度的增加,其掺气空腔及掺气浓度均有所增大,随着水流下泄掺气浓度沿程降低,达到一定距离后趋于稳定,掺气浓度值达到了减免空蚀破坏的要求;与传统阶梯溢洪道的模拟结果进行对比可知,增设前置掺气坎后,既可以增加前几级阶梯的掺气浓度使水流提前达到水气平衡,也没有降低阶梯式溢洪道的消能率,为解决传统阶梯溢洪道中出现的工程难题提供了一种新思路。     

地下厂房施工过程的三维非线性数值模拟分析

根据冗各电站地下厂房开挖支护的施工顺序,以隐式杆单元模拟锚杆,以壳单元模拟混凝土喷层,采用三维非线性有限元技术,对洞室群的开挖支护动态过程进行了模拟计算。通过三维非线性有限元计算分析得到:洞室群动态开挖过程中围岩应力变形的分布规律,围岩塑性区的发展规律,锚杆受力变化情况。计算结果表明:整个开挖过程中,洞周围岩位移变化规律正常,量值较小,塑性区主要分布在洞室周边,围岩稳定性较好;但在洞室交叉口处围岩的变形较大,出现较大范围的塑性区,在此基础上提出了支护措施优化方案,并对优化方案的效果进行了评价。     

Call for Papers

正As the eldest and most distributed professional journal of water industry,Water Wastewater Engineering(W WE)gained very wide acceptance from the colleagues working in this field in this country since start publication in 1964.Now it is administrated by the Ministry of Construction of the People’s Republic of China and sponsored by the China Civil Engineering Society etc.     

Evaluation of freshwater mussel relocation as a conservation and management strategy

The relocation of unionacean mussels is commonly used as a conservation and management tool in large rivers and streams. Relocation has been used to recolonize areas where mussel populations have been eliminated by prior pollution events, to remove mussels from construction zones and to re-establish populations of endangered species. More recently, relocation has been used to protect native freshwater mussels from colonization by the exotic zebra mussel Dreissena polymorpha. We conducted a literature review of mussel relocations and evaluated their relative success as a conservation and management strategy. We found that 43% of all relocations were conducted because of construction projects that were forced to comply with the Endangered Species Act 1973 and that only 16% were monitored for five or more consecutive years. Most (43%) relocation projects were conducted from July to September, presumably a period when reproductive stress is relatively low for most species and the metabolic rate is sufficient for reburrowing in the substrate. The mortality of relocated mussels was unreported in 27% of projects; reported mortality varied widely among projects and species and was difficult to assess. The mean mortality of relocated mussels was 49% based on an average recovery rate of 43%. There is little guidance on the methods for relocation or for monitoring the subsequent long-term status of relocated mussels. Based on this evaluation, research is needed to develop criteria for selecting a suitable relocation site and to establish appropriate methods and guidelines for conducting relocation projects.     

基于模型试验的河床砂砾石层基本特性研究

为了经济可靠地确定深厚覆盖层的基本特性参数,以大渡河双江口水电站坝基河床砂砾石层基本特性研究为工程背景,进行大尺寸模型试验,研究河床砂砾石层的旁压模量和动探击数随密度、级配以及上覆压力的变化规律。根据室内模型试验结果,结合现场旁压试验及钻孔试验成果,推断出坝址区河床砂砾石相关层位的密度,并依此进行砂砾石室内力学试验,获得设计所需力学参数。研究成果可为深厚覆盖层基本特性测试提供新的方法。     

SPATIAL AND TEMPORAL WATER QUALITY VARIABILITY IN AQUATIC HABITATS OF A CULTIVATED FLOODPLAIN

The floodplains of lowland rivers contain diverse aquatic habitats that provide valuable ecosystem services but are perturbed when intensively cultivated. Hydrologic, water chemistry and biological (fish) conditions in five aquatic habitats along the Coldwater River, Mississippi, were measured for more than 4 years: the river, two severed meanders that functioned as backwaters, a managed wetland and an ephemeral channel draining cultivated fields. Off‐channel habitats were connected to downstream regions 0.10% to 32% of the dry season and 24% to 67% of the wet season. The median temperatures for the five monitored sites ranged from 18°C to 23°C, the median total solids concentration for all sites was 135 mg L^?1, the median total phosphorus was 0.29 mg L^?1 and the median total nitrogen was 1.56 mg L^?1. Chemical and physical water quality displayed strong seasonal differences between the wet winter/spring and the dry summer/fall periods so that temporal variation consisted of gradual seasonal trends superimposed on strong diurnal variations. All off‐channel habitats exhibited periods of hypoxia and temperatures >30°C during the dry season. Between‐site gradients of water and habitat quality were strongly coupled to water depth and runoff loading. The rehabilitation of one backwater by increasing water depth and diverting agricultural runoff was associated with improved water quality and fish species richness relative to an adjacent untreated backwater. The diversion of polluted runoff and the use of water control structures to maintain greater water depth were observed to be effective management tools, but the former reduces the water supply to habitats that tend to dry up and the latter reduces connectivity. Published in 2011 by John Wiley & Sons, Ltd.     

基于BP神经网络-马尔科夫链模型的隧道围岩位移预测

在隧道工程施工中,围岩位移预测起着很重要的作用。将BP神经网络-马尔科夫链模型引入到隧道围岩位移预测中来,通过对训练样本的学习,利用BP神经网络实现了对位移时间序列的滚动预测,同时得到了实测值与预测值的相对误差;在此基础上利用马尔科夫链对相对误差进行修正,有效地提高了预测结果的精度。并将该模型应用于某公路隧道拱顶下沉位移时序预测中,结果表明该模型具有精度高、科学可靠的特点,为隧道围岩变形的预测提供了新的途径。     

Spatio‐temporal variation of gross CO2 and CH4 diffusive emissions from Australian reservoirs and natural aquatic ecosystems,and estimation of net reservoir emissions

Carbon dioxide (CO₂) and methane (CH₄) diffusive emissions were measured during two field surveys in Queensland and Tasmania, Australia, using the floating chamber method. Bubbling and degassing emissions in 2010 were estimated in Koombooloomba Dam reservoir using only inverted funnels and gas concentrations, respectively. A total of 14 reservoirs and 16 rivers and lakes were sampled from 2006 to 2010. Spatial variation was substantial within each water body, as well as between them. The main drivers of diffusive emission variation were physiographic region and climate, with a clear demarcation being observed between diffusive emissions from tropical Queensland and temperate Tasmania, and between the humid West Coast Range (Tasmania) and dry Central Plateau (Tasmania). Higher CO₂ and CH₄ diffusive emissions were observed during the dry season, when long water residence times would promote organic matter degradation. Estimated total gross emissions, including diffusive, bubbling and degassing emissions, for Koombooloomba Dam reservoir were about 1.5 × 10⁶ t CO₂eq km² per year, or 24 × 10⁶ t CO₂eq per year. This corresponds to a plant emission factor of 3.18 kg CO₂eq MWh^?1. Using an estimate of terrestrial emissions derived from literature data for the Tully River catchment area, rough estimated net emissions from the catchment area are about 44 kt CO₂eq per year, or 5.83 kg CO₂eq MWh^?1, which is in the lower range of the studied reservoirs.     

Short communication. Pipelines as a refuge for freshwater snails

In the lower River Murray, Australia, populations of gastropods have declined markedly over the past 40 years. Of the native fauna of about 18 species, only the ancylid Ferrissia petterdi remains common (but in patches), and another five species feature in sporadic local resurgences. Until recently the viviparid Notopala was thought to be extinct. The introduced physid Physa acuta is widespread, but in low numbers. The decline probably is associated with flow regulation, high turbidity and the introduction of common carp. Snail populations have persisted, however, in irrigation pipelines fed from the river, where they periodically cause blockages. This paper reports the discovery of the only known populaion of Notopala hanleyi in a pipeline where the inner wall accumulates microbial and other organic matter, providing high quality food for snails. In the Murray before regulation most of the periphytic biomass was probably microbial, as fluctuating water levels would have maintained littoral communities in a highly productive, early state of succession his postulated that, by stabilizing seasonal water levels, regulation has promoted the production of filamentous green algae, an inferior food source, and so displaced snail populations from the open aquatic environment.     

Automated system for removal and pneumatic transport of fly ash from electric precipitator hoppers

A system for removal and pneumatic transport of fly ash is examined, in which air pulses act on batches (pistons) of ash formed in a duct. Studies are made of the effect of several physical parameters on the force required to displace a piston of ash and these serve as a basis for choosing a system for removal and pneumatic transport of ash simultaneously from several hoppers of an electric precipitator. This makes it possible to separate the ash particles according to size without introducing additional components. Formulas are given for calculating the structural and dynamic parameters of this system and measurements of indirect dynamic parameters are used to calculate the input-output characteristics of the system. In order to optimize the system, configurations for summing several ducts into a single transport duct for pneumatic ash transport are proposed. Some variants of dry ash utilization and the advantages of producing of size-separated particles are considered. __________ Translated from élektricheskie Stantsii, No. 2, pp. 26–30 (2008).     

The flood pulse advantage and the restoration of river-floodplain systems

The ‘flood pulse advantage’ is the amount by which fish yield per unit mean water area is increased by a natural, predictable flood pulse. Evidence for this increase is presented from tropical and temperate fisheries. It is argued that increasing multispecies fish yield by restoring the natural hydrological regime is consistent with increasing production of other trophic levels and with restoration from ecological and aesthetic viewpoints. When applied to a river-floodplain system, this restoration would provide a large, self-sustaining potential for recreation, commercial exploitation, and flood control. An interim ‘natural flood pulse’ restoration approach is proposed for systems modified for navigation. This approach approximates the natural hydrological regime in a river reach and is intended as a first step in the long process of restoring the watershed.