弯曲复式河道水流特性数值模拟研究

为了解二维、三维模型在弯曲复式河道水流数值模拟中的应用情况,利用物理模型试验数据验证二维模型的计算结果,并对断面水面线进行了分析。可以看出,二维数模不适用于弯道水流的局部模拟,而适用于宏观水流流动的模拟。采用三维模型分析了弯曲复式河道中的二次流现象,结果表明,三维数模对于弯道水流的二次流、垂线流速分布模拟效果比较理想,可以得到弯曲河道水流运动的基本规律。     

Sediment management and flow patterns at river bend due to triangular vanes attached to the bank

Triangular vanes are hydraulic structures used for bank protection and habitat restoration for fish and other aquatic organisms. There are limitations on the design criteria for this newly-introduced structure; therefore, the main goal of this paper is to present test results carried out on different alternatives of multiple vanes with different spaces between the vanes under different hydraulic conditions in a 90-degree mild flume bend. In addition, 3D components of flow velocity were measured in tests with and without an installed single vane. The triangular vanes create a counterclockwise secondary flow cell near the outer bank, which counteracts the clockwise main secondary flow cell in the bend for a distance of about 5le (le is the vane's effective length) downstream of the vane's position. With multiple vanes in place, the thalweg was found to be shifted toward the flume midway from the outer bank. Moreover, by increasing the space between the triangular vanes, the scour around the vane's tip and its development to the outer bank increased. Therefore, it is concluded that triangular vanes perform best when they are spaced at 5le or less.     

叶片浸入深度对搅拌机内部流场影响仿真

为了研究叶片浸入深度对搅拌机内部流场的影响规律。应用Fluent计算流体动力学软件对搅拌机内部流场进行三维数值模拟,采用非结构化四面体网格,利用多重参考系方法,选用非稳态Mixture多相湍流计算模型,分析了搅拌机内部流体浓度、速度和湍动能等参数随叶片浸入深度不同而产生的变化和分布情况,揭示其内部的流动规律。模拟结果表明:中心搅拌机械在叶片轴线下方存在流动呆滞区,造成混合不畅;叶片的浸入深度对搅拌机内部湍动能值影响较小,但是对其固相分布却产生重要影响,因此要合理选择叶片的浸入深度;叶片的浸入深度等于液体高度的1/2,能够达到最佳的混合效果。研究结果对于揭示搅拌机械内部流场的流动规律,以及设备的优化设计和运行管理提供了参考依据。     

运西水电站竖井贯流式水轮机性能优化

采用雷诺时均方程(RANS),选择S-A湍流模型,运用SIMPLEC算法,利用CFD数值模拟技术,数值模拟了不同方案的运西水电站水轮机流道内流场,分析了转轮直径、叶片翼型、叶片个数、叶片安放角、转轮轮毂、转轮转速、导叶翼型、导叶轴线与机组中心线夹角、导叶个数、叶片及导叶安装位置、导叶开度对水轮机性能的影响,叶片数为3时水轮机装置性能较优,机组最高效率点分别在转速为187.5r/min、导叶个数为15时出现。对原有流道可改变部件做适当优化后,将优化后的转轮应用于电站进行数值计算,根据全流道的数值模拟结果,预测电站改造后机组的水力性能。根据数值计算的结果制作模型水轮机和真机进行模型试验和真机测试。结果表明,数值模拟结果与模型实验以及现场运行结果曲线的变化趋势一致,数值模拟结果基本能够准确反映电站的外特性和内部流场特征。     

连续微弯弯道水力特性试验及模拟研究

为了研究河流的连续微弯弯道水力特性,通过建立曲折系数为1.07的连续弯道模型进行试验,并利用Reynolds应力模型进行模拟计算,从水面线、流速场、弯道环流及强度等方面研究了小曲折系数连续弯道水力特性。结果表明:Reynolds应力模型能够较好地模拟连续弯道水流;在同一断面,近凸岸的纵向流速垂线分布接近对数流速分布,近凹岸的纵向流速垂线分布呈随相对水深增大而先增大后减小的规律,呈现“凸肚”形;在弯道环流方面,呈现非对称的双环流结构;水面和槽底处的环流强度大于水体中部,凹岸的环流强度大于凸岸的环流强度。成果为研究小曲折系数弯道的河流水力特性提供了借鉴与参考。     

急弯段闸孔出流的弯道水流特性研究

在河弯处修建水工建筑物时,研究弯道水流特性对水工建筑物布置的影响十分重要。采用RNCκ-ε紊流模型对急弯段闸孔出流的弯道水流进行了三维数值模拟。通过模拟计算,比较分析了急弯段不同闸位、不同流量条件下闸孔过流时的流速分布、紊流动能、压强分布和环流等相关水流特性与变化规律。分析研究结果表明,闸坝位于弯道上游时,弯道对闸坝过流的影响最小,但需对闸坝下流弯道凸岸岸坡附近区域采取一定的防护措施;闸坝布置在弯道中游时,过闸水流受弯道的影响最小,闸室水流的稳定性、闸门的工作安全以及闸墩的空蚀破坏都是实际工程中需要注意的重点。数值模拟验证与物理模型试验结果吻合较好,计算精度较高,能够满足相关计算研究要求。     

竖缝式鱼道结构及水力特性研究

随着越来越多大坝堤堰的修建,鱼类的洄游和繁殖受到了严重的影响。为了保持鱼类的生存繁衍,许多水利枢纽工程中都建有鱼道。研究利用fluent软件模拟了竖缝式鱼道的流场,并用模型试验对数值模拟进行了验证,分析了竖缝式鱼道导板的长度及导角大小对鱼道内流场的影响。研究结果表明:在鱼道流量及水池长宽比一定的情况下,若不考虑边壁的阻碍作用,导角越大,竖缝射流的衰减速度越快,主流轨迹的弯曲程度也越大,也越容易冲撞到边壁;导板的长度基本上对主流的扩散及衰减没有影响,但能通过改变主流在鱼道内的位置来改变边壁对流态影响程度。     

NUMERICAL AND EXPERIMENTAL RESEARCH ON CURRENT GENERATION IN DEEPWATER OFFSHORE BASIN

During the design and construction of the deepwater offshore basin, its current generation system is considered to be one of the key technologies. In this article, the state-of-the-art deepwater offshore basin at Shanghai Jiaotong University was examined as a case study. Different 3-D numerical models of the current generation system were developed and calculated. The uniformity of flow field in the basin, such as horizontal and vertical current velocity profiles, were calculated in detail. Besides, a 1:10 scaled model test was also carried out. The current velocities at different locations in the basin were measured and compared with the calculated results. It is concluded that satisfactory agreement can be resulted between the numerical simulation and model test. In addition, it is suggested that transition sections and turning vanes need to be set in inflow and outflow culverts to improve the uniformity of flow field in the basin. And the hydraulic performance of the deepwater current generation system can meet the requirements of model tests in deep water.     

二维溃坝洪水波演进的数值模拟

采用基于MacCormack预测-校正技术的隐式数值格式求解控制水流运动的二维浅水方程，建立了模拟大坝瞬间全溃或局部溃倒所致的洪水演进过程数学模型．应用该模型对矩形明渠中缓、急流过渡的水面曲线进行了数值计算，并与理论解进行了比较。最后用该模型预测了矩形河道中大坝瞬间局部溃倒时下游有多个障碍物的洪水演进过程，算例说明该数学模型对模拟溃坝洪水波很有效。     

导流板对桥墩周围紊动特性的影响

水流通过桥墩在桥墩区域形成复杂的三维流场,会对桥墩底部冲刷和桥区通航产生很大的影响,所以控制桥墩紊流区水流形态十分重要。采用RNGκ-ε紊流模型对桥墩绕流进行三维数值模拟,在墩尾设置不同长度导流板,计算分析墩周围的水流紊动强度值。设置导流板后,墩周围X/D=0~5.3断面的水流最大紊动强度值明显减小,而墩后的紊动强度普遍有减小趋势,且长度不同的导流板对同一墩型的绕流控制作用不同。合适长度的导流板能束窄紊动强度变化值σ0.1的范围,即能减小紊流宽度。     

基于FLOW-3D软件的溢洪道三维水流数值模拟

采用FLOW-3D水流计算软件模拟了溢洪道挑流消能的三维水流流场,并通过调整溢洪道平面布置、增设贴角和改变预挖冲坑范围等措施对溢洪道原设计方案进行了优化。结合水工模型试验成果,对原设计方案和优化方案的水流流态、流速分布和水面线等水力特性进行了对比分析。数值模拟计算结果与水工模型试验比较吻合,说明优化方案的有效性,也进一步表明三维数值模拟的可行性。     

导流屏在河流弯道护岸工程中的应用研究

本文分析了弯道水流的基本特性，阐述了充分淹没在水下的导流屏特性和由此引起的河床剪应力之间的关系，给出了弯段河道导流屏护岸原理及设计方法。工程实例表明：本文给出的理论和设计方法是合理的。     

弯道处溢流坝闸孔水流水力稳定性分析及优化

为研究弯道对溢流坝闸孔水流水力特性的影响,探求弯道处水流进入闸室运动状态的优化措施,以某水库弯道处溢流坝为例建立物理模型。通过对不同流量级下试验数据分析,探讨弯道处某水库溢流坝闸孔挑流对左右岸稳定性、闸孔泄流能力的影响,同时运用 Flow-3d 软件设置导墙措施进行优化数值模拟。结果表明：水流在闸室以螺旋式向下泄流,且在闸室及溢流面上左右碰撞和交汇,使得水流极其不稳定,对左右岸稳定影响极大且降低闸孔泄流能力,对相邻闸孔泄流量增大值的幅度有所减小,最大差值从 1.95 m3/s 降为 0.95 m3/s;设置导墙可以有效减缓弯道对闸孔挑流的水力稳定性的影响,提高闸孔水流泄流能力,为弯道处溢流坝建设提供理论参考。     

无粘沙质床面上冲积性河湾形成和演变规律自然模型试验研究

基于雷诺方程和有限体积法建立了描述弯道水流运动的三维数学模型，并利用室内物理模型试验进行验证，验证结果表明，数学模型能够较好地模拟弯道内水流的流速分布以及湍流特征。以验证后的模型为工具，对具有不同平面形态和床面形态的弯道中的水流运动进行了模拟，模拟结果表明：弯道中浅滩和深槽相间的地形起伏加剧了断面流速分布的不均匀性，同时使得水流动力轴线更加偏向凹岸，流速的沿程变化也较平整床面更为复杂；另外，与对称型河弯（正弦派生曲线型）相比，非对称河弯（Kinoshita派生曲线型）中在两弯顶中间存在较多的低流速区，有利于泥沙的落淤，而对岸流速一般较大，形成河岸的快速崩退，这能够从一个侧面解释非对称河弯向下游方向整体的快速迁移。     

180°弯曲水槽内床面冲淤演化过程数值模拟

为准确掌握180°弯曲水槽内床面冲淤特征及其演化过程,采用基于非结构化三角形网格的三维流动和地形冲淤数值模型对180°弯曲水槽内床面的冲淤演化过程进行复演。运用标准k-ε紊流模型和显式2步投影方法求解RANS方程,推移质输沙率选取VanRijn输沙公式计算,对于二次流强度较强、横向坡度对输沙方向影响较大的强弯曲水槽,采用方便实用的Engelund方法计算横向底坡所引起的输沙方向的偏移,同时对河床变形所引起的河床临界起动切应力变化进行修正及对流动和地形冲淤相同时间步模拟非恒定的河床冲淤演化过程。与试验测量结果对比显示数值模型对强弯曲水槽冲淤特征有较好的模拟效果;Engelund方法对计算输沙方向偏移角度具有明显的改进;模型同样也具备复演内床面非恒定冲淤演化过程的能力。     

三峡水轮机全流道三维流动数值模拟研究

本文使用商业CFD软件FLUENT,开发了部分接口程序,进行了全流道原型水轮机三维湍流数值模拟研究,计算对象是中国水利水电科学研究院机电研究所为三峡右岸开发的水轮机模型,该水力模型有完整的模型试验资料,可用于检验计算结果。水轮机全流道三维湍流数值模拟,计算区域为包括蜗壳、固定导叶、活动导叶、转轮和尾水管的全部流道。模拟中控制方程采用了三维时均N—S方程、湍流模型采用两方程RNG k-ε模型,数值方法采用贴体坐标的有限体积法。共进行了3个开度条件下的计算,每个开度各进行4个典型工况的三维湍流流场模拟,通过数值方法求解控制方程,获得了全流道的流速和压力分布。计算结果表明流速和压力分布合理,数值计算得到的效率与试验得到的效率进行比较,结果吻合良好。     

Flow over embankment gabion weirs in free flow conditions

In this study, a series of laboratory tests were performed to investigate the effects of side ramp slope, crest length, and porous media properties on the flow regimes, water-surface profiles, discharge coefficients, and energy dissipation in embankment gabion weirs with upstream and downstream slopes. 24 physical models of solid and gabion weirs with three different upstream/downstream slopes (90°, 45° and 26.5°) were created. To investigate the complexity of flow over the porous-fluid interface and through the porous material, three-dimensional (3D) numerical simulations were developed. In numerical simulation, the standard k-ε turbulence model was utilized. A structured mesh domain was used to simulate the physical model. Water surface profiles above the porous weirs were used for comparison between the numerical simulations and measured data. These comparisons helped determine variables in the numerical simulations. Numerical simulation enables visualization of streamlines around and through the gabion weirs. In addition, mean stream wise velocity profiles above and within the porous structures were obtained. Numerical simulations showed that a reduction in the slope of the upstream face leads to an increased curvature of streamlines and the velocity distribution exhibits a non-uniform wavy shape due to the geometrical properties of the weirs. As the velocity profiles move downstream, the velocity distribution within the porous structures were more affected by the presence of the pores. The experimental results show that decreasing upstream slopes, from 90° to 26.5°, leads to decreased discharge coefficients. However, in all cases, gabion weirs lead to greater discharge coefficients than those of similar solid weirs. For milder side slopes, discharge ratios (flow passing through all faces of the gabion weirs over the inlet discharge) decreased nonlinearly. Moreover, with increasing the inlet discharge, relative energy dissipation was reduced up to 45% in gabion weirs.     

Simulation of subcritical flow pattern in 180° uniform and convergent open-channel bends using SSIIM 3-D model

In meandering rivers, the flow pattern is highly complex, with specific characteristics at bends that are not observed along straight paths. A numerical model can be effectively used to predict such flow fields. Since river bends are not uniform-some are divergent and others convergent-in this study, after the SSIIM 3-D model was calibrated using the result of measurements along a uniform 180° bend with a width of 0.6 m, a similar but convergent 180° bend, 0.6 m to 0.45 m wide, was simulated using the SSIIM...     

杨房沟水电站截流进占水力特性数值模拟分析

为分析比选杨房沟水电站截流工程进占方案,通过建立相关三维数值模型,采用水力模拟计算技术对单戗堤单向及双向立堵进占方式的水流条件进行了计算,并将单向立堵进占数值模拟计算结果与物理模型试验结果进行了对比分析。结果表明:三维数值模拟与试验结果较为吻合,计算结果偏于安全;同时指出在现场条件允许的情况下,双向立堵进占能够有效降低该工程截流难度。     

基于正交设计的黄池沟退水道弯道体型优化的数值模拟分析

为探求黄池沟退水道弯道的合理体型,采用正交设计与数值模拟相结合的方法研究了体型参数对弯道水流的影响。选取弯道宽度、弯道曲率半径、纵向坡度3个主要影响参数按正交试验设计,确定了9组正交试验方案,利用经水工模型试验结果验证的数学模型对正交试验方案进行模拟,分析了体型参数对弯道及下游陡坡段横向水位差的影响。结果表明,3个体型参数影响作用由大到小依次为纵向坡度、弯道宽度和弯道曲率半径;坡度为显著影响因素,且平坡最佳,弯道曲率半径和弯道宽度影响不显著,据此推荐合理体型参数为坡度取0,弯道宽度和弯道曲率半径采用原设计值。