Z形薄壁堰过流能力试验

鉴于Z形堰的水流特性及过流能力尚未见到相关报道,为研究Z形堰的过流能力,采用概化水工模型,进行了6个堰型方案、12组流量的水工模型试验。结果表明,Z形堰的过流能力大于直线堰,且Z形堰的展宽比越大,流量扩大倍数越大;Z形堰的流量计算可采用通用的堰流公式,其综合流量系数与堰上水深、堰高、展长、前堰宽、后堰宽等因素有关,展宽比、前后堰宽比越大,流量系数越大;堰上水深与堰高之比越大,流量系数越小。利用试验数据给出了考虑堰上水深与堰高之比、展宽比、前后堰宽比等因素的Z形堰流量系数估算公式。     

An iterative hydraulic design methodology based on numerical modeling for piano key weirs

Piano Key Weir (PKW) is a special type of overflow weir which provides an improved discharge capacity with its increased crest length. Increased discharge capacity makes this weir an attractive alternative in the rehabilitation of existing spillways. After the introduction of this new weir type, many experimental and numerical studies are conducted to understand the effect of the numerous geometrical parameters on the discharge capacity. However, empirical discharge formulas suggested by different researchers are not conforming to a unique expression mostly due to dependence on the experimental conditions from which they are derived. A numerical approach is used in the present study to investigate the dependence of discharge capacity of a PKW unit on several geometric parameters. Numerical models are developed and three-dimensional velocity fields are computed using FLOW-3D® software. Discharge efficiency of a PKW over an equivalent linear sharp-crested weir is evaluated within the practical range of parameters from 145 numerical solutions for 29 different PKW models. Numerically obtained data is used to form dimensionless expressions for the weir height and length as function of discharge efficiency which are proposed to facilitate an iterative numerical solution to meet the design requirements of a given project. This approach allows cost optimization while dimensioning the PKW for the required hydraulic capacity. The design procedure based on iterative numerical solutions is described and exemplified.     

Physical modelling of pool and weir fishways with rock weirs

The flow characteristics of pool and weir fishways with rock weirs were studied through physical modelling. Detailed flow measurements were obtained using an acoustic Doppler velocimeter to understand how weir geometry, discharge, and bed slope affect flow patterns, velocity, turbulence kinetic energy, turbulence intensity, and Reynolds shear stresses in the fishway. The weir geometries used in this study are similar to those typically used for river restoration projects. The use of a V‐shaped rock weir was found to reduce the mean streamwise velocity in the pools by about 20% but more than double the maximum velocity magnitude. Two stage–discharge relationships were developed using the standard weir equation and a modified discharge coefficient to account for both flow over the weir and orifice flow through the base of the weir. The use of V‐shaped rock weirs has the potential to offer significant advantages in assisting multispecies fish migration. The results of this study can be applied to the hydrotechnical design of pool and weir fishways with rock weirs and for river restoration projects.     

Study of Flow Over Side Weirs Under Supercritical Conditions

The present study focuses on the application of momentum principle to the analysis of spatially varied flow under supercritical conditions. Experimental studies were conducted on rectangular side weirs of different lengths and sill heights fitted in the test section of a rectangular aluminium channel that was built in a tilting flume. Measurements of discharges in the main channel and through the side weir were done separately. A pitot tube with direction finder was used to determine the velocities and angle of spill flow with the side weir. Depths of flow were measured both in longitudinal and transverse directions at regular intervals and their profiles were studied. Experiments were conducted with different test plates and flow conditions in the main channel. Coefficients of discharge were computed using momentum principle for different Froude numbers (between 1.5 and 3). The variation of discharge coefficient of the side weir as a function of Froude number was found to exhibit a non-linear relationship. Discharges over side weirs were computed using the computed coefficients of discharge for different Froude numbers and it was verified with the observed discharges. Coefficients of discharge were also computed using energy principle for different Froude numbers. Chi-square test was done between observed discharges over side weirs and discharges computed using momentum and energy principles, it was found that momentum principle is fitting better. Variation of the ratios of longitudinal components of velocity vector of spill flow to the mean velocity of the main channel flow at upstream end of the side weir with Froude number was found to exhibit a non-linear relationship. Variation of the discharge ratios of spill flow and main channel discharges with Froude number was also studied.     

迷宫堰过流能力数值模拟

以鞍子河水库溢洪道为研究对象,采用FLUENT软件、利用 k～ε湍流模型和VOF法处理自由水面,对迷宫堰过流能力进行数值模拟。数值模拟结果与试验结果对比表明,采用的模型能够较精确的模拟迷宫堰的过流能力。计算发现,迷宫堰在堰上水头较高的情况下,对计算模型的边界条件进行优化后,可以减小计算误差,为迷宫堰的工程设计提供参考依据。     

Mathematical modeling of flow discharge over compound sharp-crested weirs

Water measurements play a pivotal role in hydraulic and environmental management of river systems, irrigation and drainage networks, and sewer conduits. Due to effective limitations of simple sharp crested weirs, recently compound sharp crested weirs have attracted great attention of civil engineers. With this type of weir, flow discharge is measured with a reasonable sensitivity over a wide range of flow rates. In this paper, the Shiono and Knight (SKM) quasi 2-D mathematical model has been numerically solved for discharge prediction of compound weirs, based on the assumption of flow similarity between compound sharp crested weirs and compound open channels. The modeled results are compared with the experimental data and the conventional method (linear combination of theoretical equations of simple weirs). The comparisons revealed that the proposed method shows improved discharge calculation within 3.8 percent absolute mean error while the traditional method has more than 12.5 percent error.     

琴键堰增设护墙对泄流能力影响的模型试验研究

为探究在堰顶增设护墙以及护墙高度对琴键堰泄流能力的影响,通过模型试验对比分析了8种不同高度护墙琴键堰的泄流能力,并通过数值模拟对5种不同高度护墙琴键堰各溢流前缘的泄流量、水面形态以及流速分布等特征进行了分析。结果表明:相较于基础体型,增设护墙提高了进口和出口宫室的泄流效率和泄流量占比,提高了侧堰泄流量,减少了侧堰溢流碰撞,提高了水流下泄流速,从而提升了琴键堰的泄流能力;增设护墙高度为堰高的13%时,泄流能力提升最大,当相对水头 H/P<0.20、0.20相似文献   

琴键堰不同堰高泄流特性的数值模拟

采用基于VOF自由面捕捉的全三维紊流数值模拟的方法,对琴键堰各个流量断面进行了泄流量的分析。通过比较五种不同堰高的琴键堰的泄流情况,分别从各个断面的流量所占的百分比、单宽流量和泄流效率等方面,得出了堰高对各断面的影响,从而得出了堰高越高泄流能力越强的结论,为今后的工程和研究提供参考。     

Hydraulic and turbulence structure of triangular labyrinth weir‐pool fishways

Detailed laboratory experiments were conducted to analyze and evaluate a new weir‐pool fishway design. The new design consisted of a series of one‐cycle, triangular labyrinth weirs that formed a weir‐pool fish passage. Hydraulic characteristics of flow over the proposed fishway were examined for three pool lengths and a wide range of discharges. It was found that the new design had superior discharge capacity over classical weir‐pool fishways in plunging flow regime. Spatial and point analyses of measured velocity data were carried out to understand turbulence structure and distribution of turbulent flow. The power dissipation per unit volume was calculated for different tests, and it varied nonlinearly with discharge. Based on the limiting criteria for energy dissipation rates of different fish species, the maximum operating discharge for different slopes was extracted for the proposed design. The model‐to‐prototype scaling analysis was performed based on the recommended scaling factor of three for prototype. It was found that the approach velocity of prototype increased by 12%, whereas the total discharge increased by more than five times. The contour plots of time‐averaged velocity indicated that the proposed fishways offered diversified flow fields without exceeding the maximum velocity above the standards recommended for weir‐pool fishways. To study the size, direction, and periodicity of turbulent eddies, magnitude of the most energetic eddy and dominant frequencies were extracted using power spectrum analysis. Quadrant analysis consistently showed that Reynolds shear stresses in ejection and sweep events became weaker as the pool length increased. The small region of strong ejection and sweep events evidenced a good resting place for fish migration, whereas the generated turbulence was large enough to attract fish species to use the passage.     

Modified theoretical stage-discharge relation for circular sharp-crested weirs

A circular sharp-crested weir is a circular control section used for measuring flow in open channels, reservoirs, and tanks. As flow measuring devices in open channels, these weirs are placed perpendicular to the sides and bottoms of straight-approach channels. Considering the complex patterns of flow passing over circular sharp-crested weirs, an equation having experimental correlation coefficients was used to extract a stage-discharge relation for weirs. Assuming the occurrence of critical flow over the weir crest, a theoretical stage-discharge relation was obtained in this study by solving two extracted non-linear equations. To study the precision of the theoretical stage-discharge relation, 58 experiments were performed on six circular weirs with different diameters and crest heights in a 30 cm-wide flume. The results show that, for each stage above the weirs, the theoretically calculated discharge is less than the measured discharge, and this difference increases with the stage. Finally, the theoretical stage-discharge relation was modified by exerting a correction coefficient which is a function of the ratio of the upstream flow depth to the weir crest height. The results show that the modified stage-discharge relation is in good agreement with the measured results.     

琴键堰泄流能力影响因素与计算分析研究

近年来特大洪水和超标准洪水频繁发生,已建水利工程泄流能力不足问题日益突出。琴键堰在适当低水头条件下具有高效泄流效率。归纳了琴键堰主要结构参数对其泄流能力的影响及最佳取值,总结了琴键堰流态对泄流能力的影响,分析了琴键堰发生低水头行为的条件参数。通过对比现有琴键堰泄流能力估算公式,并结合国内外已有试验数据,采用遗传算法拟合推导了基于溢流堰轴线长度L、堰宽W、堰长B、堰高P、进出水宫室宽度比W_i/W_o及上下游倒悬长度比B_o/B_i流量系数计算式,整体误差小于6%。该式计算简单,适用于琴键堰整体泄流能力估算,可根据实际需求选取合适的估算公式。琴键堰主要结构参数的最佳取值及泄流能力的计算方法可为超标准洪水条件下泄流建筑物设计或改建提供估算依据。     

袁河新泉乡段梯级溢流堰水动力模拟及侵蚀分析

为了分析梯级溢流堰对袁河新泉乡段河道行洪及河床抗冲的影响,优化河道治理工程中溢流堰布置,建立了将拦河溢流堰作为闭边界条件的二维水动力数值模型,采用非结构化网格的有限体积法,对比分析了十年一遇洪水情况下梯级溢流堰建设前后河道水动力、河道水位、流场沿程变化特征,讨论了溢流堰布置对河道防洪及冲刷的影响。结果表明,在十年一遇洪水情况下溢流堰会抬升河道水位,平均增加0.49 m,满足河道行洪要求;梯级溢流堰使河道整体形成人工“阶梯深潭”体系,河道流速在空间上发生明显的异质性,堰上流速下降幅度较堰下流速大;水流发生急流与缓流之间交替,水流紊动强烈,加剧了水流能量损失,有效降低流速,减轻了河道冲刷,有利于稳定河岸结构。     

侧壁角对梯形琴键堰泄流能力的影响

梯形琴键堰(T.P.K堰)是琴键堰(P.K堰)的进一步发展,具有泄流能力强、受地形限制影响小等优点。为了研究不同侧壁角对T.P.K堰泄流能力的影响,采用RNG k-ε湍流模型VOF法追踪自由表面,对5种不同侧壁角的堰型进行三维数值模拟。结果表明:α＜0°对T.P.K堰的泄流能力产生不利影响;随着侧壁角的增大,泄流能力得到了提升,当α=9°时,泄流量不再提高。利用数值模拟的优点,分别对T.P.K堰不同溢流前缘的泄流能力进行研究,并且揭示了侧壁角对泄流能力的内在影响机理。     

某水电站琴键堰体型优化试验研究

琴键堰是一种新型的高效溢流堰,以曲折的堰顶结构来增加溢流前缘总长度,使得其泄流能力远超直线堰。针对某拟建水电站琴键堰泄流能力不足的问题,提出了增加展宽比(L/W)、增加堰高(P)和增加堰高且减少单元数(n)的优化方案,并通过物理模型试验进行验证,得到了满足设计要求的推荐方案。此外,本研究还探讨了水工模型类别(整体及断面模型)和比尺效应对琴键堰泄流能力的影响。通过对比分析优化方案可知：方案M1(展宽比L/W由7.75增至8.88)中,琴键堰泄流能力得到了一定程度的提高,但泄流能力仍不满足设计要求;方案M2(堰高由4.50 m增至6.50 m)和M3(堰高由4.50 m增至6.90 m,单元数由17.5个减至8.5个)中,琴键堰泄流能力显著增加,该两种方案皆可满足设计要求。试验结果表明：与琴键堰整体模型相比,其断面模型测得的泄流能力偏大约6%;对于琴键堰,当模型堰上水头大于2.50 cm时,比尺效应对琴键堰泄流能力的影响可以忽略。     

Predicting velocity in bendway weir eddy fields

Rehabilitation of the Middle Rio Grande (MRG) in central New Mexico has become necessary because of changes in morphology resulting from the installation of dams, and because of habitat restoration considerations for the endangered Rio Grande silvery minnow (Hybognathus amarus). Bendway weirs are erosion control and channel‐stabilization structures placed transverse to the channel flow that have been increasingly used to prevent river migration while simultaneously enhancing aquatic habitat. Plans for rehabilitation along the MRG include the use of bendway weirs; however, past projects using these structures have relied on field experience and engineering judgment rather than specific design guidelines. A physical model of a reach of the MRG was constructed to develop empirical design equations for eddy velocities in bendway weir fields. Data from physical model simulations were used to develop two empirical expressions for predicting eddy velocities behind bendway weirs, along with two expressions for predicting velocities at the toe of installed weirs. These equations relate the velocity found after bendway weir installation to weir design characteristics and pre‐weir channel conditions. A designer can use the described approach to predict velocities in eddies and velocities at the toe of bendway weirs using only weir design variables and pre‐weir channel conditions, and thus avoid some of the uncertainty with weir design that previously existed. Copyright © 2009 John Wiley & Sons, Ltd.     

The behaviour of Pacific salmonid smolts during passage over two experimental weirs under light and dark conditions

Little is known of how fish respond to the hydraulic environment associated with diversion or bypass structures at hydroelectric power installations. To address this lack of knowledge, this paper presents results from a study to assess how three species of Pacific salmonid smolt (Oncorhynchus spp.) responded to distinct gradients of velocity and depth associated with two submerged weirs as they passed through an experimental flume at McNary Dam (Columbia River, USA) under illuminated and dark conditions. Migrating smolts entered one of two available treatment channels as coherent schools from which individuals would either disassociate from the group and pass over the weirs, or would reject them by swimming upstream. Alternatively, fish maintained position at the upstream end of the flume by swimming into the flow. The response of smolts to velocity and depth gradient and light condition varied between species, and route of passage was influenced by fork length. Initial channel selection and school size was not influenced by weir type, although schools resided longer within the short‐weir channel. The majority of smolts (70%) entered the treatment channels facing downstream (negative rheotaxis), but switched orientation at the crests of the weirs. This switch in orientation occurred farther downstream in the short‐weir treatment and for the largest smolts. The variation in response of different species of smolts to hydraulic gradients has important implications for the design of screening mechanisms used at hydroelectric power installations to divert migrant juvenile salmonids. Published in 2006 by John Wiley & Sons, Ltd.     

Bendway weirs: Could they create habitat for the endangered Rio Grande silvery minnow

Rehabilitation of the Middle Rio Grande in central New Mexico has become necessary to mitigate the effects of over a century of water and land development. The primary driving force behind rehabilitation efforts is the federally endangered Rio Grande silvery minnow (Hybognathus amarus). Bendway weirs, erosion control and channel‐stabilization structures placed transverse to the channel flow, have been used to prevent river migration while enhancing aquatic habitat. Habitat improvement plans on the Middle Rio Grande include the installation of bendway weirs, but the potential benefits of these structures for Rio Grande silvery minnow are unknown. We conducted a theoretical study on the flow conditions created by bendway weirs to determine if it is possible to create physical habitat for Rio Grande silvery minnow while simultaneously protecting the riverbank. Our study suggested that bendway weir installation could lead to the reduction of downstream displacement of Rio Grande silvery minnow eggs, the creation of Rio Grande silvery minnow feeding and refugia habitat, and the creation of drought or low flow habitat through scour hole formation. We also noted that the weirs could also serve as potential habitat for predators, and suggest further studies to better quantify the possible role of bendway weir installation. Copyright © 2009 John Wiley & Sons, Ltd.     

The influence of discharge and temperature on the ability of upstream migrant adult river lamprey (Lampetra fluviatilis) to pass experimental overshot and undershot weirs

The efficiencies of fish passes specifically designed and constructed to facilitate the movement of a limited number of species and life‐stages past structural barriers are likely to decline as site‐specific conditions shift with a changing climate. There is a need to develop realistic fish passage criteria based on understanding swimming capability and behaviour of multiple species in relation to temperature and flow. The influence of temperature and discharge on behaviour and ability of groups of migrating adult river lamprey (Lampetra fluviatilis), a threatened species, to pass a small overshot or undershot weir at night was investigated using a large experimental flume. Lamprey approached the weirs less, and more often maintained station by using the oral disk to attach to structure, under high flows. Oral disk attachment was more commonly observed during tests employing the undershot weir. Upstream movement tended to be in close proximity to the channel walls and floor where, compared to the mid‐channel, velocities were generally lower and velocity vectors more likely to be in a direction other than the bulk flow. Upstream movement was positively related to temperature, and was higher for the overshot weir. Weir passage rate was higher for undershot than overshot weirs, and negatively related to the maximum velocity at the weir. Passage rate was low when maximum velocities at the weir exceeded 1.5 m s^?1, although some fish passed at c. 1.7 m s^?1. Passage efficiency, the number of weir passes as a percentage of the number of approaches, was also higher for the undershot weir, but was not affected by discharge because lamprey approached less frequently at high flows. This study provides fish passage criteria under realistic conditions for an infrequently studied anguilliform species of conservation concern and provides a methodological perspective by which to improve fishway suitability for a wider range of species subject to changing climate. Copyright © 2010 John Wiley & Sons, Ltd. This article was published online on March 3, 2010. An error was subsequently identified in the Article title. This notice is included in the online and print versions to indicate that both have been corrected [April 12, 2010].     

To swim or to jump? Passage behaviour of a potamodromous cyprinid over an experimental broad‐crested weir

Physical stressors, such as man‐made obstacles, are considered one of the main causes that negatively affect freshwater fish. Even small weirs may impact fish populations, including potamodromous cyprinids, by partially or totally blocking upstream migratory movements. Some studies have addressed the effect of key hydraulic parameters on upstream movements past small weirs, but little is known on how these parameters interact to induce swimming or jumping behaviour in negotiating such obstacles. This study aims to evaluate the passage behaviour (swimming vs. jumping) of Iberian barbel (Luciobarbus bocagei), a potamodromous species, over an experimental small broad‐crested weir, considering the effect of different plunge pool depths (D), waterfall heights (H), and weir discharges (Q). Results revealed that passage behaviour was highly dependent on combinations of plunge pool depths and waterfall heights. Barbel navigated most configurations by swimming (overall outcomes: 81.5% swimming vs. 18.5% jumping), except the ones with the higher waterfall heights (25 cm) tested. Therefore, higher waterfalls proved to be preponderant in the switching of passage behaviour from swimming to jumping. Regarding the discharge over the 1‐m‐wide weir (overall outcomes: 85% swimming vs. 15% jumping), contrary to what was expected, there was no evidence that passage behaviour was discharge‐related, for the range of discharges tested (25–100 L/s). These results are useful to identify potential migration obstacles and should be taken into consideration in river restoration projects and when designing fishways for potamodromous cyprinids.     

Numerical simulation of overbank flood discharges

A full computer based investigation of the factors influencing the modelling of overbank flood discharges has been carried out. Several floods of differing magnitudes and peak curvatures were routed down regular channels using an implicit finite difference scheme and the influence of time and distance steps used for the numerical solution of the flow equations were investigated. Spillage over sharp crested weirs was assumed to satisfactorily simulate the overbank flood discharge; the importance of a correct estimation of the coefficient of discharge was also checked. It was shown that sensibly chosen values of the time step had little effect on the simulations. This was also true for the value of the coefficient of discharge when the sideweir flow was predominately drowned, but not for free flow conditions. It was also shown that close spacing of computational nodes was required at the onset of overbank flow to accurately simulate the overflow and also model the occurrence of large water level gradients.