基于熵产理论的水泵水轮机反S区水力损失机理分析

水泵水轮机在水轮机工况运行时易进入反S不稳定区,影响机组的安全稳定运行。传统压差法在计算水力损失时不能获得损失的具体分布和详细来源,因此水泵水轮机在反S区水力损失机理仍有待深入研究。本文采用雷诺时均方法对某原型抽蓄电站水泵水轮机在活动导叶开度分别为12°和35°下的反S区运行工况进行了数值模拟,基于熵产理论对各个过流部件和不同类型的水力损失进行了定量分析,并结合流场分布情况进一步明确了水力损失的分布特点和产生原因。结果表明,水泵水轮机进入反S区会引起导叶段水力损失占总水力损失的比例逐渐增大,而转轮段水力损失逐渐减小。在不同类型的能量损失中,湍流熵产占据主导,壁面熵产次之,直接熵产最小。随着水泵水轮机进入深度反S区,转轮区湍流熵产损失较大区域从转轮进口的叶片压力面转移到转轮出口叶片吸力面。水泵水轮机位于反S区时,转轮对水流做功输入能量,使无叶区总压大幅上升,活动导叶开度增大会显著增大无叶区水流能量幅值。     

水泵水轮机四象限工作区流动特性数值分析

抽水蓄能电站工况转换频繁,过渡过程中水泵水轮机可历经全特性4个象限,不稳定的复杂流动演变使过渡过程中事故频发。本文针对某低比转速模型水泵水轮机进行四象限全流道数值计算,得到同一开度下水轮机内部流态的演变规律。结果显示,在水泵区部分负荷工况,导叶区产生旋转失速现象,失速区的个数随流量大小变化;失速涡阻塞流道,使局部压力升高,产生周向传播的低频压力波动。在水泵制动区,当转速较高时,离心力作用使得水流不能均匀进入转轮,在转轮内产生旋转失速现象。在水轮机反"S"区,转轮进口产生的回流漩涡结构随流量在某些工况点的突变,导致沿转轮进口展向的流速分布呈现随流量而突变的现象。入流分布在飞逸点附近的突变使水流对转轮的做功特性发生突然变化,可能是导致空载不稳定的原因。     

水泵水轮机泵工况压力脉动和转轮受力特性

为研究水泵水轮机在泵工况下的内部流态变化对压力脉动和转轮叶片受力的影响,采用 SAS－SST 湍流模型对某一模型水泵水轮机的多个非设计工况进行非定常数值模拟,分析了水轮机 内部流态对导叶与转轮之间无叶区、尾水管内的压力脉动和转轮叶片径向受力的影响。结果表明: 在流量为 40% ～80%设计流量时,导叶区内产生旋转失速,转失速涡团初生于固定导叶进口,并随着流量的降低向活动导叶进口发展,且覆盖区域逐渐增大。旋转失速使压力和过流沿周向不均匀分布, 导致压力脉动和转轮径向受力波动大幅上升。在40%设计流量时,失速涡团发展最为充分,无叶区 压力脉动和转轮受力波动的低频分量幅值最高。旋转失速产生的低频脉动可向尾水管传播,形成的低 频压力脉动幅值约为无叶区低频脉动幅值的10%。当流量低于 40%设计流量时,导叶区旋转失速消失,复杂的涡结构形成的压力脉动低频成分没有周期性。此外,转轮进口的流动分离使尾水管内产生复杂的回流涡结构,导致尾水管内形成频谱丰富的压力脉动; 流量降低使转轮进口回流涡结构的湍动 能增加,导致尾水管内压力脉动幅值大幅上升。小流量工况下,转轮进口的涡结构演变是转轮径向力波动的主要影响因素。     

水泵水轮机泵工况压力脉动和转轮受力特性

为研究水泵水轮机在泵工况下的内部流态变化对压力脉动和转轮叶片受力的影响,采用SAS-SST湍流模型对某一模型水泵水轮机的多个非设计工况进行非定常数值模拟,分析了水轮机内部流态对导叶与转轮之间无叶区、尾水管内的压力脉动和转轮叶片径向受力的影响。结果表明:在流量为40%～80%设计流量时,导叶区内产生旋转失速,转失速涡团初生于固定导叶进口,并随着流量的降低向活动导叶进口发展,且覆盖区域逐渐增大。旋转失速使压力和过流沿周向不均匀分布,导致压力脉动和转轮径向受力波动大幅上升。在40%设计流量时,失速涡团发展最为充分,无叶区压力脉动和转轮受力波动的低频分量幅值最高。旋转失速产生的低频脉动可向尾水管传播,形成的低频压力脉动幅值约为无叶区低频脉动幅值的10%。当流量低于40%设计流量时,导叶区旋转失速消失,复杂的涡结构形成的压力脉动低频成分没有周期性。此外,转轮进口的流动分离使尾水管内产生复杂的回流涡结构,导致尾水管内形成频谱丰富的压力脉动;流量降低使转轮进口回流涡结构的湍动能增加,导致尾水管内压力脉动幅值大幅上升。小流量工况下,转轮进口的涡结构演变是转轮径向力波动的主要影响因素。     

基于熵产理论的水轮机尾水管涡带研究

为了研究水泵水轮机部分负荷工况尾水管涡带产生的原因和压力脉动特性,本文以模型水泵水轮机为研究对象,对内部流动进行了全流道三维数值模拟并采用熵产理论进行了分析。计算结果分析表明:数值模拟与实验值吻合较好;固定导叶和蜗壳内的总熵产很小,而转轮和尾水管内较大,在小流量工况叶片压力面产生的流动分离会导致高熵产率分布区域的出现,并且会随着流量的进一步减小而扩大;在部分负荷出现了粗壮型和纤细形两种涡带,均呈现螺旋形,涡带的形成与叶片出口环量偏离零环量有很大关系;涡带的出现会在尾水管内形成漩涡,阻塞尾水管通道,涡带跟随转轮同方向旋转,但是转速更低,因此尾水管出现幅值较大的低频压力脉动。     

水泵水轮机全流道“S”特性区数值分析

抽水蓄能电站在水电中扮演着极其重要的角色,其机组水泵水轮机的“S”特性区流动情况是研究的重点。以自主研发的某水泵水轮机为研究对象,根据模型试验结果的“S”特性曲线,选取其中小导叶开度的“S”特性曲线,结合SST k-w湍流模型,运用ANSYS-CFX软件对曲线上部分工况点进行了数值分析。数值分析工况包括水轮机工况、飞逸工况、制动工况和反水泵工况,通过计算得到了单位流量和单位转速的关系曲线,所得曲线与模型试验曲线较为吻合。计算结果表明：在制动工况和反水泵工况时,固定导叶、活动导叶和转轮区域内均存在较多的旋涡性回流,为较为不稳定的工况。转轮区域内流动速度极低,叶片中间位置有无规则性回流,相邻的两个叶片头部之间形成横向流动的水环,水环在离心力的作用下阻挡水流进入流道,从而大大减小了转轮的过流能力,这可能是导致水泵水轮机在制动工况下单位转速降低的重要原因。     

基于熵产理论的水泵水轮机泵模式水力损失分布

基于熵产理论,研究原型水泵水轮机在泵模式不同流量工况下的水力损失空间分布及不稳定流动诱导的主要水力损失存在的位置和变化。结果表明：随着流量增加,总熵产与压差法水力损失变化一致,先显著减小后逐渐增大。间接熵产、直接熵产和壁面熵产与总熵产的变化趋势一致,且间接熵产和直接熵产占主导地位。间接熵产和直接熵产的分布与湍动能的分布基本一致,但直接熵产更靠近主涡区,而间接熵产在流场中具有更宽的分布范围。水泵水轮机流动区域内的水力损失位置强烈依赖于流动条件。小流量工况下高水力损失主要源于无叶区的高速环流、活动导叶区的旋涡以及尾水管弯肘段和直锥段的壁面分离,而蜗壳的水力损失较小。最优工况下的水力损失较小,主要源于叶片尾迹和少数固定导叶流道的旋涡。大流量工况下高水力损失主要源于水流对活动导叶的冲击和不稳定流动在固定导叶区的扩散,以及蜗壳进口处周向间隔分布的旋涡和高速流动,而尾水管的水力损失极小。     

长短叶片混流式水轮机三维非定常流数值模拟

为探究长短叶片混流式水轮机在不同导叶开度下运行时内部水流流动的特点,基于流场数值模拟的计算方法对长短叶片混流式水轮机进行了全流道三维非定常湍流计算。结果表明,在不同开度下,转轮与导叶交界面处压力脉动主频皆为转轮转频与叶片数的乘积,且在小流量工况下主频振幅最大。当水轮机在小流量工况下运行时,尾水管涡带呈螺旋形,且绕转轮转轴顺时针旋转,与转轮旋转方向相同;当水轮机在额定工况下运行时,尾水管无涡带产生;当水轮机在大流量工况下运行时,尾水管涡带呈细长的圆锥形。     

某低水头混流式水轮机叶道涡特性数值分析

采用数值模拟手段,研究低水头混流式水轮机叶道涡的水力特性,依托某低水头混流式水轮机模型转轮试验结果和数值计算结果,选取三个单位转速下出现叶道涡的工况,基于N-S方程及SST湍流模型对水轮机进行单流道、全流道、定常和非定常流动数值模拟,分析叶道涡复杂流动的水力特性和压力脉动。结果表明,在叶道涡初生工况,叶片上冠正背面均有部分脱流现象,随着水流在叶片内部运动,转轮出口处,靠近上冠区域有较明显的脱流漩涡和失速区,这部分区域也是叶道涡产生的集中区域。分析转轮内部各个监测点的压力脉动数据,发现转轮内部各个测点会出现有规律的1倍转频的低频脉动和24倍高频脉动,1倍低频脉动与转轮自身转速有关,24倍高频脉动与活动导叶数量有关,是动静干涉影响的结果。测点位置的流态越差,该测点的压力脉动幅值会越高。     

水轮机振动成因分析及其防止

水电站的混流型水轮机的转轮形式与水机进口导叶叶型是按恒定的理想流体运动设计的.在设计工况下,水轮机具有高效率,水流从辐向进入蜗壳,在经过转轮叶片时为无撞击进口与法向出口,水流从轴向离开转轮,并进入尾水管而流入下游.在设计工况下,导叶全开,并与水流方向相平行.如机组实际出力比设计额定出力为小,则它处于非设计工况.处于非设计工况是由两种原因所导致:一是机组水头的改变;二是机组过流量的改变.而过流量的改变则是通过机组导叶的开度改变来实现的.     

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。     

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。     

Serial discontinuities in a Rocky mountain river. I. Distribution and abundance of plecoptera

Samples were taken year-round at eleven sites along the altitudinal profile (2900-1400 m a.s.l.) of the Gunnison River, a 329 km tributary of the Colorado River, to document the distribution of the Plecoptera and to evaluate responses to hypolimnial-release dams in the headwaters and middle reaches. Twenty-two species were present, with the greatest species richness occurring in an unregulated segment upstream of the middle reach dams; average nymphal biomass over the study period (175 organisms, 395 mg dry mass m^?2) was also greatest in this segment. Only four species (58 organisms, 48 mg m^?2) were present in the tailwaters of the headwater dam and values were greatly reduced (nine species; 35 organisms, 180 mg m^?2) below the middle reach dams. The stonefly community recovered ca. 80 km downstream from the last dam (15 species; 244 organisms, 250 mg m^?2), apparently in response to natural resetting of environmental conditions corresponding to those above the middle reach dams. At the most downstream site (11) only four species (four organisms, 16 mg m^?2) were present. The observed distributional pattern is a classic serial discontinuity in response to hypolimnial stream regulation in a temperate latitude river.     

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。     

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.     

浙江省水域调查录入系统的设计和应用

浙江省水域调查录入系统将调查数据与电子地图相整合,对分类水域数据进行统计计算,并对输入数据进行合理性和完整性检查,得到调查范围内现有水域的详细数据,实现了水域调查数据输入、计算、统计和查询的数字化管理,提高了工作效率和工作质量,为各地下阶段水域保护规划编制和水域管理工作提供了数据支持。对该系统的设计原则、功能和技术设计等作了介绍。     

基于CT-连续加荷水泥乳化沥青混凝土细观损伤规律研究

利用CT技术对水泥乳化沥青混凝土的细观损伤过程进行实时扫描观测,获得了混凝土试件在连续加荷下的CT图像。通过采用直观分析法、CT数分析法、CT数与损伤变量关系3种方法分析表明,水泥乳化沥青混凝土的破坏过程可分为压密、扩容、裂纹扩展、破坏4个阶段,同时混凝土在受压过程中具有韧性,在极限荷载之前各断面处于压密和微扩容的强化阶段,极限荷载之后混凝土从损伤到破坏发展比较平稳。     

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.