1、1核准通过，归档资料。未经允许，请勿外传！毕业设计（论文）外文翻译题 目 姚家河水电站 溢流坝及消能工优化设计专 业 水利水电工程 9JWKffwvG#tYM*Jg t 是时间;A i是小数区开放流标方向; 5VF是在每个单元的流体体积分数; 密度; p 是静水压力; gi是在标方向的引力;f i代表一个需要封闭湍流模型的雷诺应力。通过数值 FLOW-3D 模型求解水流经过反弧段的流速变化准确地追踪流体体积（VOF模型）函数代表了流体占据的比例量的自由表面。 两方程的整理总结的理论模型（RNG 模型）用于湍流闭合。 RNG 模型来描述更准确的低强度的湍流流动和流具有较强的剪切区域。流区域被细分
2、成固定的矩形单元网格。每个单元有关联的当地所有相关的变量的平均值。所有变量都位于网格中面孔（交错网格布置） 。弯曲的障碍、壁面边界或其他几何特征是嵌入在网状定义分区和分开流动的变量。4.结论在这项研究中,流动特性如流量、水的表面,堰顶S形的泄洪道承受了巨大的压力,和垂直速度及压力分布在考虑模型规模和表面粗糙度的影响利用商业CFD模型进行详细的研究,验证了FLOW-3D被广泛用于溢洪道流分析领域。探讨了尺度和表面粗糙度的影响,六例被采用。也就是对数值模拟液压平滑(PR00),k = 0.5毫米(PR05)和k = 3.0毫米(PR30)进行了调查研究和对原型粗糙度影响(PR05)、1/50模型(
3、M50)、1/00模型(M100)、1/200模型(M200)的调查进行的尺度效应。在建模过程中按比例改变后的模型、网格分辨率、表面粗糙度、上游边界条件和几何相似度调整来排除不同的数值误差。重要的仿真结果包括以下几点:1)流量略微减少排放做为该模型表面粗糙度的高度和长度尺度的增加标准。水面波动是可以忽略不计的，和一些由于发生改变的表面粗糙度和模型的规模引起的波峰压力变化。由于数值误差表面粗糙度是渺小的,如果我们仅仅使用一般的建筑材料和粗糙高度的尺度效应，如长度尺度比小于100年或200年，模型就会出现在一个可接受的误差范围内。2)建模结果表明,增加的比率引起长度尺度相似现象，是由于日益增长的表
4、面粗糙度造成的。如果hm选中作为参考点,速度的模型比在模型参考点以下,但速度的原型是低于按比例改变后的模型参考点。表面粗糙度和尺度效应的更为严重低于参考点。3)溢洪道顶的压力会有所不同。在改变表面粗糙度和模型的规模后，垂直压力分布几乎还是一样上网。4)最高速度稍微减少，任何部分的表面粗糙度和长度尺度比例增加。出现最大速度的垂直位置位于较低位置处作为上层水源，并且在溢洪道正前方很远处成直线增加。6文章出处：土木工程研究所 KSCE.第 2/2005 年 3 月 9 日，第 161169外文原文：Analysis of Flow Structure over Ogee-Spillway in Co
5、nsideration of Scale and Roughness Effects by Using CFD Model By Dae Geun Kim* and Jae Hyun Park* AbstractIn this study, flow characteristics such as flowrate, water surfaces, crest pressures on the ogee-spillway, and vertical distributions of velocity and pressure in consideration of model scale an
6、d surface roughness effects are investigated in detail by using the commercial CFD model, FLOW-3D, which is widely verified and used in the field of spillway flow analysis. Numerical errors in the discharge flowrate, water surfaces, and crest pressures due to the surface roughness are insignificant
7、if we just use a general roughness height of construction materials, and the scale effects of the model are in an acceptable error range if the length scale ratio is less than 100 or 200. The roughness and scale effects are more severe below hm, where the maximum velocity occurs in perpendicular coo
8、rdinate to the weir crest. The velocity of the prototype is larger than that of the scaled model below but the phenomena are contrary above hm. Maximum velocity at any section slightly decreases as the surface roughness and the length scale ratio increase. The vertical location where maximum velocit
9、y occurs is located on a lower position as the upstream water head increases and the location almost linearly increases with the distance from the front of the spillway. Keywords: FLOW-3D, ogee-spillway, roughness effect, scale effect1. IntroductionThe ogee-crested spillways ability to pass flows ef
10、ficiently and safely, when properly designed and constructed, with relatively good flow measuring capabilities, has enabled engineers to use it in a wide variety of situations as a water discharge structure (USACE, 71988; USBR, 1973).The ogee-crested spillways performance attributes are due to its s
11、hape being derived from the lower surface of an aerated nappe flowing over a sharp-crested weir. The ogee shape results in near-atmospheric pressure over the crest section for a design head. At heads lower than the design head, the discharge is less because of crest resistance. At higher heads, the
12、discharge is greater than an aerated sharp-crested weir because the negative crest pressure suctions more flow. Although much is understood about the general ogee shape and its flow characteristics, it is also understood that a deviation from the standard design parameters such as a change in upstre
13、am flow conditions, modified crest shape, or change in approach channel owing to local geometric properties can change the flow properties. For the analysis of the effects, physical models have been used extensively because a spillway is very important for the safety of dams. The disadvantages with
14、the physical models are high costs and that it can take fairly long time to get the results. Also, errors due to scale effects may increases in severity as the ratio of prototype to model size increases. So, numerical modeling, even if it cannot be used for the final determination of the design, is
15、valuable for obtaining a guide to correct details because computational cost is low relative to physical modeling.In the past few years, several researchers have attempted to solve the flow over spillway with a variety of mathematical models and computational methods. The main difficulty of the prob
16、lem is the flow transition from subcritical to supercritical flow. In addition, the discharge is unknown and must be solved as part of the solution. This is especially critical when the velocity head upstream from the spillway is a significant part of the total upstream head.An early attempt of mode
17、ling spillway flow have used potential flow theory and mapping into the complex potential plane (Cassidy, 1965). A better convergence of Cassidys solution was obtained by Ikegawa and Washizu (1973), Betts (1979), and Li et al. (1989) using linear finite elements and the variation principle. They wer
18、e able to produce answers for the free surface and crest pressures and found agreement with experimental data. Guo et al. (1998) expanded on the potential flow theory by applying the analytical functional boundary value theory with the substitution of variables to derive nonsingular boundary integra
19、l equations. This method was applied successfully to spillways with a free drop. Assy (2000) used a stream function to analyze the irrotational flow over spillway crests. The approach is based on the finite difference method with a new representation of Neumanns problem on 8boundary points, and it g
20、ives positive results. The results are in agreement with those obtained by way of experiments. Unami et al. (1999) developed a numerical model using the finite element and finite-volume methods for the resolution of two dimensional free surface flow equations including air entrainment and applied it
21、 to the calculation of the flow in a spillway. The results prove that the model is valid as a primary analysis tool for the hydraulic design of spillways. Song and Zhou (1999) developed a numerical model that may beapplied to analyze the 3D flow pattern of the tunnel or chute spillways, particularly
22、 the inlet geometry effect on flow condition. Olsen and Kjellesvig (1988) included viscous effects by numerically solving the Reynolds-averaged Navier-Stokes (RANS) equations, using the standard-equations to model turbulence. They showed excellent agreement for water surfaces and discharge coefficie
23、nts. Recently, investigations of flow over ogee-spillways were carried out using a commercially available computational fluid dynamics program, FLOW-3D, which solves the RANS equations (Ho et al., 2001; Kim, 2003; Savage et al., 2001). They showed that there is reasonably good agreement between the
24、physical and numerical models for both pressures and discharges. Especially, Kim (2003) investigated the scale effects of the physical model by using FLOW-3D. The results of numerical simulation on the series of scale models showed different flow discharges. Discharge and velocity of larger scale mo
25、dels has shown larger value than the smaller scale models.Existing studies using CFD model mostly deal with the models applicability to discharge flowrate, water surfaces, and crest pressures on the spillway. In this study, flow characteristics such as flowrate, water surfaces, crest pressures on th
26、e spillway, and vertical distributions of velocity and pressure in consideration of model scale and surface roughness effects are investigated in detail by using commercial CFD model, FLOW-3D, which is widely verified and used in the field of spillway flow analysis. The objective of this study is to
27、 investigate quantitatively the scale and roughness effects on the flow characteristics by analyzing the computational results.2. Scaling and RoughnessA hydraulic model uses a scaled model for replicating flow patterns in many natural flow systems and for evaluating the performance of hydraulic stru
28、ctures. Shortcomings in models usually are termed scale effects of laboratory effects. Scale effects increase in severity as the ratio of prototype to model size increases or the number of physical processes 9to be replicated simultaneously increases. Laboratory effects arise because of limitations
29、in space, model constructability, instrumentation, or measurement. Generally, steady nonuniform flow characteristics in open channel flow with hydraulic structures can be explained as a following relationship (ASCE, 2000).where Sw is water surface slope, So is channel bottom slope, h is water depth,
30、 k is roughness height of solid boundary, V is flow velocity, g is gravitational acceleration, and v, are dynamic iscosity, density, surface tension of water, respectively. Eq. (1) states that water surface profile is expressed as bottom slope, relative roughness height, Froude number, Reynolds numb
31、er and Weber number. Similarity of variables in Eq. (1) between scaled model and prototype is maintained for the hydraulic model to properly replicate features of a complicated prototype flow situation.Generally, geometric similarity (So) is achieved and experiments are carried out by using Froude n
32、umber similarity in the hydraulic Table 1. Approximate Values of Roughness Height, kmodel on the open channel flow and hydraulic structures. Water is used to analyze the flow characteristics of scaled model, thus modeling accuracy is compromised because the properties of water are not scaled. So, a
33、small scale model may causes a failure to simulate the forces attendant to fluid properties such as viscosity and surface tension, to exhibit different flow behavior than that of a prototype. Moreover, relative roughness height of the scaled model cannot be exactly reproduced because materials of ex
34、periment are limited.Previous study on the scale limits of hydraulic models leads to some guidelines. The Bureau of Reclamation (1980) used length scale ratios of Lr = 30100 for models of spillways on large dams. And model flow depths over a spillway crest should be at least 75 mm for the 10spillway
35、s design operating range. The average roughness height for a given surface can be determined by experiments. Table 1 gives values of roughness height for several kinds of material which are used for construction of hydraulics structures and scaled models (Hager, 1999).To determine quantitatively how
36、 scale and roughness effects influence the model results, it is possible to use a series of scale models with different surface roughness including prototype. But the hydraulic model experiments are expensive, time-consuming, and there are many difficulties in measuring the data in detail. Today, wi
37、th the advance in computer technology and more efficient CFD codes, the flow behavior over ogee-spillways can be investigated numerically in a reasonable amount of time and cost.3.Governing Equations and Computational Scheme The commercially available CFD package, FLOW-3D, uses the finite-volume app
38、roach to solve the RANS equations by the implementation of the Fractional Area / Volume Obstacle Representation (FAVOR) method to define an obstacle (Flow Science, 2002). The general governing RANS and continuity equations for incompressible flow, including the FAVOR variables, are given bywhere ui
39、represent the velocities in the xi directions which are x, y, z-directions; t is time; Ai is fractional areas open to flow in the subscript directions; VF is volume fraction of fluid in each cell; is density; p is hydrostatic pressure; gi is gravitational force in the subscript directions; fi repres
40、ents the Reynolds stresses for which a turbulence model is required for closure.To numerically solve the rapidly varying flow over an ogee crest, it is important that the free surface is accurately tracked. In FLOW-3D, free surface is defined in terms of the volume of fluid (VOF) function which repr
41、esents the volume of fraction occupied by the fluid.A two-equation renormalized group theory models (RNG model) was used for turbulence closure. The RNG model is known to describe more accurately low intensity turbulence flows and flow having strong shear regions (Yakhot et al., 1992).11The flow reg
42、ion is subdivided into a mesh of fixed rectangular cells. With each cell there are associated local average values of all dependent variables. All variables are located at the centers of the cells except for velocities, which are located at cell faces (staggered grid arrangement). Curved obstacles,
43、wall boundaries, or other geometric features are embedded in the mesh by defining the fractional face areas and fractional volumes of the cells that are open to flow.4. ConclusionsIn this study, flow characteristics such as flowrate, water surfaces, crest pressures on the ogee-spillway, and vertical
44、 distributions of velocity and pressure in consideration of model scale and surface roughness effects are investigated in detail by using commercial CFD model, FLOW-3D which is widely verified and used in the field of spillway flow analysis. To investigate the scaling and roughness effects, six case
45、s are adopted. Namely, numerical modeling on the hydraulically smooth (PR00), k = 0.5 mm (PR05), and k = 3.0 mm (PR30) for the investigation of roughness effects and prototype (PR05), 1/ 50 model (M50), 1/00 model (M100), 1/200 model (M200) for the investigation of scale effects are carried out. In
46、the modeling of the scaled model, grid resolution, surface roughness,and upstream boundary conditions were adjusted as the geometric similarity to exclude a generation of different numerical error. The important simulation results comprise the following: 1) The discharge flowrate decreases slightly
47、as surface roughness height and the length scale of the model to the prototype increase. The water surface fluctuation is negligible and some crest pressure variation occurs with a change of surface roughness and model scale. Numerical errors due to the surface roughness are insignificant if we just
48、 use a general roughness height of construction materials and the scale effects of the model are appeared in within an acceptable error range if the length scale ratio is less than 100 or 200. 2) The modeling results show that increasing of the length scale ratio give rise to similar phenomena due t
49、o increasing of the surface roughness. If hm is chosen as a reference point, the velocity of the prototype is larger than that of the scaled model below the reference point but the velocity of the prototype is smaller than that of the scaled model above the reference point. The roughness and scale effects are more severe below the reference point. 3) The pressures on the spillway crest are somewhat different with a change of the surface roughness and model scale. But the vertical pressure distributions are almost same to each other regardless of 12the surface roughness
