外文翻譯--使用cfd模型分析規(guī)模和粗糙度對反弧泄洪洞的影響

1、<p><b>　　畢業(yè)設計（論文）</b></p><p><b>　　外文翻譯</b></p><p>　　題 目 姚家河水電站 </p><p>　　溢流壩及消能工優(yōu)化設計</p><p>　　專 業(yè) 水利水電工程 </p><

2、p>　　班 級 五 班 </p><p>　　學 生 敖 杰 </p><p>　　指導教師 鐘 亮 </p><p><b>　　重慶交通大學</b></p><p><b>　　2012 年</b>&

3、lt;/p><p>　　使用CFD模型分析規(guī)模和粗糙度對反弧泄洪洞的影響</p><p>　　作者 Dae Geun Kim1and Jae Hyun Park2</p><p><b>　　摘 要</b></p><p>　　在這項研究中，利用CFD模型、FLOW-3D模型詳細調查流量特性如流量、水面、反弧溢洪道上的峰值

4、壓力，并考慮到模型規(guī)模和表面粗糙度對速度和壓力的垂直分布特征的影響，因此，在領域中被廣泛驗證和使用。由于表面粗糙度數(shù)值的誤差是微不足道的，對于流量，水面平穩(wěn)，波峰壓力影響較小。但是我們只是使用長度比例小于100或200在可接受的誤差范圍的建筑材料一般粗糙度高度和規(guī)模效應的模型，最大速度在垂直的坐標堰發(fā)生更嚴重的粗糙度和規(guī)模效應。原型的速度比縮尺比模型的更大，但現(xiàn)卻相反的。在任何一節(jié)的最大速度略有降低或者表面粗糙度和長度的比例增加。最大速

5、度出現(xiàn)在上游水頭的增加幾乎呈線性增加溢洪道前的距離和位置較低的垂直位置位上。</p><p>　　關鍵詞：FLOW-3D，反弧溢洪道，粗糙度效應，規(guī)模效應</p><p><b>　　1.簡介</b></p><p>　　工程師在大多數(shù)情況下都選著設計建造具有過流高效、安全地反弧溢洪道，并且它在使用過程中具有良好的測量能力。反弧溢洪道的形狀是從

6、較高頂堰的直線段流到半徑R的網弧形段，在反弧附近的大氣壓力超過設計水頭。在低于設計水頭時波峰阻力減少。在高水頭的時候，頂堰的大氣壓較高產生負壓使水流變得更緩。雖然這是關于一般反弧的形狀和其流動特性的理解，但是從上游流量條件下的變化、修改的波峰形狀或改變航道由于局部幾何性質等的標準設計參數(shù)的偏差都會改變的水流的流動性，影響的分析結果。物理模型被廣泛的用來確定溢洪道非常重要的大壩安全。物理模型的缺點是成本高，它可能需要相當長的時間得到的結果

7、。此外，由于規(guī)模效應的誤差的嚴重程度增加原型模型的大小比例。因此在指導以正確的模型細節(jié)時，計算成本相對較低物理建模、數(shù)值模擬，即使它不能被用于為最終確定的設計也是非常寶貴的資料。</p><p>　　在過去的幾年中，一些研究人員試著解決各種數(shù)學模型和計算方法的流量超過溢洪道的問題，主要困難是從亞臨界流到超臨界流過渡。此外，速度是未知的也必須作為解決方案的一部分，速度水頭是上游泄洪時上游水頭的重要組成部分。<

8、/p><p>　　泄洪流量建模最早被試用在卡西迪（1965）復雜的平面勢流理論和映射中。一個更好的解決卡西迪的問題的利用非線性有限元和變分原理方案被貝茨（1979年），李等提出 。這個方案能夠自由表面和波峰壓力并且發(fā)現(xiàn)現(xiàn)實與實驗數(shù)據的相似性。然后，郭（1998）擴大了對勢流理論的運用與分析，對邊界值理論推導出邊界積分方程的變量代換，此方法已成功應用到了自由下落的溢洪道中。艾斯（2000）采用流函數(shù)分析對溢洪

9、道波峰無旋流動。有限差分法的方法給邊界點上的問題提供了積極的成果。結果與實驗的方式獲得這些關系。1990年，開發(fā)了一個采用有限元和有限體積方法為二維自由表面流動方程，包括空氣夾帶的決議，并將其應用到在泄洪流量計算數(shù)值模型。實驗證明該模型是有效的溢洪道水力設計作為主要分析工具。宋和周（1999）開發(fā)了一個數(shù)值模型可能被用來分析隧道或槽溢洪道，特別是進口水流條件幾何效應的三維流模式。奧爾森（1988年），通過求解雷諾數(shù)方程來解釋標準方程模型

10、湍流粘性的影響。他們表現(xiàn)出優(yōu)秀的水面和流量系數(shù)的相似。最近，在反弧溢洪道水流進行調查中發(fā)現(xiàn)，使用計算二維流體力學，三維流體學。他們還發(fā)現(xiàn)有相當不錯的物理模型和數(shù)值模型之</p><p>　　現(xiàn)有的研究大多使用CFD模型處理模型的適用性，以估算泄洪流量、水面和峰值壓力對原型的影響。在這項研究中，利用CFD模型、FLOW-3D模型通過流量、水面、溢洪道壩頂上的壓力、模型規(guī)模和表面粗糙度等流量特性對的速度和壓力的垂直分

11、布的影響。泄洪流量分析方法在溢流壩設計領域中被廣泛驗證和使用，本研究的目的是調查、定量分析的計算結果對流動特性的規(guī)模和粗糙度的影響。</p><p><b>　　2.縮放和粗糙度</b></p><p>　　一個采用在許多自然流系統(tǒng)和水工結構性能評估縮尺模型的的水力模型的缺點，通常被稱為實驗室效果的規(guī)模效應。規(guī)模效應的嚴重程度增加，比例模型的大小增加或物理過程的數(shù)量增

12、加同時增加。實驗室在空間、施工性模型、儀器儀表、或測量的限制，一般來說，水工結構的明渠流量恒定非均勻流動特性可以解釋為以下關系（ASCE，2000）。</p><p>　　Sw是水面坡度，S0所以渠道底坡，h是水深，k為固體邊界的粗糙度高度，V為流速，g是重力加速度，和V，ρ，σ分別是動態(tài)粘度厘泊，密度，水的表面張力。方程（1）水面線為底坡，相對粗糙度高度、弗勞德數(shù)、雷諾數(shù)和韋伯數(shù)表示式中的變量的相似性。方程（1

13、）之間保持正確復制功能復雜的原型流動情況的水工模型縮尺模型和原型。</p><p>　　一般來說，幾何相似并進行了實驗用液壓表1中的弗勞德數(shù)相似。粗糙高度，K的近似值</p><p>　　明渠流量和水工結構模型中水是用來分析縮尺模型的流動特性。當建模精度受到損害，水的特性是不進行縮放，一個小規(guī)模的模型可能導致失敗的模擬失敗，如粘度和表面張力的流體性質，比原型表現(xiàn)出不同的流態(tài)。此外，因為實驗

14、材料有限縮尺模型的相對粗糙度高度不能完全復制。</p><p>　　先前由于研究水力模型的規(guī)模限制導致一些誤差。Lr的尺度比率為 30?100型號的大型水壩溢洪道。和模型流深度超過溢洪道的設計水頭工作范圍至少為75毫米。對于一個給定的表面平均粗糙度高度可通過試驗確定。</p><p>　　為了確定規(guī)模和粗糙度如何影響模型結果的，實驗中使用不同的表面粗糙度和一系列與原型成比例的模型，但水工模

15、型試驗費用昂貴而且在測量數(shù)中還有許多困難。隨著計算機技術和更有效的CFD模型的進步，在一個合理的時間和金錢條件下進行反弧溢洪道的流態(tài)模型進行模擬實驗。</p><p><b>　　3.方程應用</b></p><p>　　通過CFD模型、三維流動模型，采用有限體積方法來解決RANS方程的分數(shù)面積/體積的方程表示方法來定義一個流量的實施過程。由一般平均雷諾連續(xù)性方程和不

16、可壓縮流、包括其他變??量可得：</p><p>　　其中ui代表的是X，Y，Xi方向的速度，z方向; t是時間;Ai是小數(shù)區(qū)開放流標方向; VF是在每個單元的流體體積分數(shù);ρ密度; p是靜水壓力; gi是在標方向的引力;fi代表一個需要封閉湍流模型的雷諾應力。</p><p>　　通過數(shù)值FLOW-3D模型求解水流經過反弧段的流速變化準確地追蹤流體體積（VOF模型）函數(shù)代表了流

17、體占據的比例量的自由表面。 </p><p>　　兩方程的整理總結的理論模型（RNG模型）用于湍流閉合。 RNG模型來描述更準確的低強度的湍流流動和流具有較強的剪切區(qū)域。</p><p>　　流區(qū)域被細分成固定的矩形單元網格。每個單元有關聯(lián)的當?shù)厮邢嚓P的變量的平均值。所有變量都位于網格中面孔（交錯網格布置）。彎曲的障礙、壁面邊界或其他幾何特征是嵌入在網狀定義分區(qū)和分開

18、流動的變量。</p><p><b>　　4.結論</b></p><p>　　在這項研究中,流動特性如流量、水的表面,堰頂S形的泄洪道承受了巨大的壓力,和垂直速度及壓力分布在考慮模型規(guī)模和表面粗糙度的影響利用商業(yè)CFD模型進行詳細的研究,驗證了FLOW-3D被廣泛用于溢洪道流分析領域。探討了尺度和表面粗糙度的影響,六例被采用。也就是對數(shù)值模擬液壓平滑(PR00),k

19、 = 0.5毫米(PR05)和k = 3.0毫米(PR30)進行了調查研究和對原型粗糙度影響(PR05)、1/50模型(M50)、1/00模型(M100)、1/200模型(M200)的調查進行的尺度效應。在建模過程中按比例改變后的模型、網格分辨率、表面粗糙度、上游邊界條件和幾何相似度調整來排除不同的數(shù)值誤差。重要的仿真結果包括以下幾點:1)流量略微減少排放做為該模型表面粗糙度的高度和長度尺度的增加標準。水面波動是可以忽略不計的，和一些由

20、于發(fā)生改變的表面粗糙度和模型的規(guī)模引起的波峰壓力變化。由于數(shù)值誤差表面粗糙度是渺小的,如果我們僅僅使用一般的建筑材料和粗糙高度的尺度效應，如長度尺度比小于100年或200年，模型就會出現(xiàn)在一個可接受的誤差范圍內。2)建模結果表明,增加的比率引起長度尺度相似現(xiàn)象，是由于日</p><p>　　文章出處：土木工程研究所KSCE.第2/2005年3月9日，第161?169</p><p><

21、;b>　　外文原文：</b></p><p>　　Analysis of Flow Structure over Ogee-Spillway in Consideration of Scale and Roughness Effects by Using CFD Model </p><p>　　By Dae Geun Kim* and Jae Hyun Park** &

22、lt;/p><p><b>　　Abstract</b></p><p>　　In this study, flow characteristics such as flowrate, water surfaces, crest pressures on the ogee-spillway, and vertical distributions of velocity a

23、nd pressure in consideration of model scale and 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. N

24、umerical errors in the discharge flowrate, water surfaces, and crest pressures due to the surface roughness are insignificant if we </p><p>　　Keywords: FLOW-3D, ogee-spillway, roughness effect, scale effect&

25、lt;/p><p>　　1. Introduction</p><p>　　The ogee-crested spillway’s ability to pass flows efficiently and safely, when properly designed and constructed, with relatively good flow measuring capabiliti

26、es, has enabled engineers to use it in a wide variety of situations as a water discharge structure (USACE, 1988; USBR, 1973).The ogee-crested spillway’s performance attributes are due to its shape being derived from the

27、lower surface of an aerated nappe flowing over a sharp-crested weir. The ogee shape results in near-atmospheric pressure</p><p>　　In the past few years, several researchers have attempted to solve the flow o

28、ver spillway with a variety of mathematical models and computational methods. The main difficulty of the problem is the flow transition from subcritical to supercritical flow. In addition, the discharge is unknown and mu

29、st 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.</p><p>　　An early attempt of modeling s

30、pillway flow have used potential flow theory and mapping into the complex potential plane (Cassidy, 1965). A better convergence of Cassidy’s solution was obtained by Ikegawa and Washizu (1973), Betts (1979), and Li et al

31、. (1989) using linear finite elements and the variation principle. They were able to produce answers for the free surface and crest pressures and found agreement with experimental data. Guo et al. (1998) expanded on the

32、 potential flow theory by appl</p><p>　　Existing studies using CFD model mostly deal with the model’s applicability to discharge flowrate, water surfaces, and crest pressures on the spillway. In this study,

33、flow characteristics such as flowrate, water surfaces, crest pressures on the spillway, and vertical distributions of velocity and pressure in consideration of model scale and surface roughness effects are investigated i

34、n detail by using commercial CFD model, FLOW-3D, which is widely verified and used in the field of spillway flow </p><p>　　2. Scaling and Roughness</p><p>　　A hydraulic model uses a scaled model

35、 for replicating flow patterns in many natural flow systems and for evaluating the performance of hydraulic structures. Shortcomings in models usually are termed scale effects of laboratory effects. Scale effects increa

36、se in severity as the ratio of prototype to model size increases or the number of physical processes to be replicated simultaneously increases. Laboratory effects arise because of limitations in space, model constructabi

37、lity, instrumentation, </p><p>　　where Sw is water surface slope, So is channel bottom slope, h is water depth, k is roughness height of solid boundary, V is flow velocity, g is gravitational acceleration, a

38、nd 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 number and Webe

39、r number. Similarity of variables in Eq. (1) between scaled model and prototype is maintained for the hydr</p><p>　　Generally, geometric similarity (So) is achieved and experiments are carried out by using F

40、roude number similarity in the hydraulic Table 1. Approximate Values of Roughness Height, k</p><p>　　model on the open channel flow and hydraulic structures. Water is used to analyze the flow characteristics

41、 of scaled model, thus modeling accuracy is compromised because the properties of water are not scaled. So, a small scale model may causes a failure to simulate the forces attendant to fluid properties such as viscosity

42、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</p><p>　　Previous study on the s

43、cale limits of hydraulic models leads to some guidelines. The Bureau of Reclamation (1980) used length scale ratios of Lr = 30~100 for models of spillways on large dams. And model flow depths over a spillway crest should

44、 be at least 75 mm for the spillway’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 whic

45、h are used for construction of hydrau</p><p>　　To determine quantitatively how scale and roughness effects influence the model results, it is possible to use a series of scale models with different surface r

46、oughness including prototype. But the hydraulic model experiments are expensive, time-consuming, and there are many difficulties in measuring the data in detail. Today, with the advance in computer technology and more ef

47、ficient CFD codes, the flow behavior over ogee-spillways can be investigated numerically in a reasonable amount of time </p><p>　　3.Governing Equations and Computational Scheme </p><p>　　The com

48、mercially available CFD package, FLOW-3D, uses the finite-volume approach to solve the RANS equations by the implementation of the Fractional Area / Volume Obstacle Representation (FAVOR) method to define an obstacl

49、e (Flow Science, 2002). The general governing RANS and continuity equations for incompressible flow, including the FAVOR variables, are given by</p><p>　　where ui represent the velocities in the xi direction

50、s 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

51、in the subscript directions; fi represents the Reynolds stresses for which a turbulence model is required for closure.</p><p>　　To numerically solve the rapidly varying flow over an ogee crest, it is importa

52、nt that the free surface is accurately tracked. In FLOW-3D, free surface is defined in terms of the volume of fluid (VOF) function which represents the volume of fraction occupied by the fluid.</p><p>　　A tw

53、o-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 a

54、l., 1992).</p><p>　　The flow region 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

55、 centers of the cells except for velocities, which are located at cell faces (staggered grid arrangement). Curved obstacles, wall boundaries, or other geometric features are embedded in the mesh by defining the fractiona

56、l face areas and fractional volumes of the cells that are open to flow.</p><p>　　4. Conclusions</p><p>　　In this study, flow characteristics such as flowrate, water surfaces, crest pressures on

57、the ogee-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 verif

58、ied and used in the field of spillway flow analysis. To investigate the scaling and roughness effects, six cases are adopted. Namely, numerical modeling on the hydraulically smooth (PR00), k </p><p>　　KSCE J