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研究生：	莊偉良 Chuang, Wei-Liang
論文名稱：	抽水井流場之數值模擬研究 Numerical Study on Pump Sump Flows
指導教授：	蕭士俊 Hsiao, Shih-Chun
學位類別：	碩士 Master
系所名稱：	工學院 - 水利及海洋工程學系 Department of Hydraulic & Ocean Engineering
論文出版年：	2010
畢業學年度：	98
語文別：	英文
論文頁數：	134
中文關鍵詞：	抽水井、鐘形吸入口、大渦紊流模式
外文關鍵詞：	pump sump, suction bell, Large Eddy Simulation
相關次數：	點閱：108 下載：3
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大型抽水井廣泛應用於電廠冷卻水系統、污水處理廠及防洪抽水站等，抽水井流場是否均勻且穩定為評估泵之效率及機件壽命之主要關鍵因素。過去研究以實驗探討物理模型為主，然而隨著電腦計算能力提升，三維數值模式近年來廣泛地應用於模擬抽水井模型之流場及探討其產生渦流之機制，模擬結果不僅展現一定之準確度及可靠性，相較於實驗中觀察易受限於量測方式，模擬結果可呈現模型中任一處之流場。對於評估不同形式之改善方案時，數值模擬可大量節省建構實驗模型及操作之成本。

本研究求解不可壓縮流之三維Navier-Stokes方程式及大渦紊流模式，以有限體積法離散結構及非結構之混合網格，固體邊界使用不可滑移邊界條件，而入流及出流皆給定均勻流流況。模式驗證部分，引用兩種不同型式之抽水井模型的實驗：林（2004）及Ansar等人（2001）。比較結果顯示，本模式模擬之速度剖面及流場分佈皆與實驗結果相當一致，同時不受過去僅能將具複雜形狀之鐘形吸入口簡化成簡單圓柱管的限制，具更廣泛之應用性。除此之外，Ansar等人（2002）以非黏性流模擬具橫向漸進流之抽水井流場，其模擬結果與本研究比較發現，包含主渠道之大計算域與給定已知速度剖面而取代主渠道之小計算域相比，更能模擬符合實驗量測之細部結果。

本研究進一步模擬林（2004）之抽水井模型探討吸入管內之流況，並額外考慮三種不同之分流裝置。由管內流之垂直速度分佈中發現，在鐘型吸入口內並無逆向之垂直流速，而通過吸入口喉部後，於管壁附近形成逆向流之區域。在管內渦度分佈可得知管中心附近存在一組對稱之強烈渦旋。另外在實驗上，吸入口喉部之旋轉角為評估抽水效益之主要參數，而本研究於此嘗試以渦度計算之環流量推估此參數並與實驗值比較及討論。

Large-scale hydraulic pump sumps are widely used in cooling system of power-generation plants, flooding control station, and sewage-disposal plants. It is crucial to evaluate the uniformity and stability of the pump-sump flow which has significant influence on the pump performance. For this problem, experimental approach is mainly applied in assessing such problem for many years. However, with the rapid development of the computer capability, three-dimensional numerical modeling becomes an alternative to simulate the pump-sump flows and understand the mechanism of the vortex formation. In contrast to the limitation caused by the measuring method, numerical modeling can perform the flow field anywhere in the intake model. Moreover, if several sets of modified setups are concerned, numerical modeling can reduce a great number of costs in construction and operation for experiment.

In this study, three-dimensional incompressible Navier-Stokes equation is solved, and the turbulent fluctuation is filtered and modeled by Large Eddy Simulation model. The momentum equation is discretized by Finite Volume Method in hybrid structured and unstructured grids. The solid wall is treated as no-slip condition. The uniform flow condition is employed at inflow and outflow surfaces. In this thesis, the validation on numerical model will be performed in two distinct intake models. Two experiments are cited: Lin (2004) and Ansar et al. (2001). For the comparisons in the approaching flow, including velocity profiles and flow patterns, the simulation results well agree with both experiments. Meanwhile, the simulation consisting of a complicated suction bell is made in contrast to consider it as simple circular cylinder in previous study. Furthermore, instead of replacing the main channel with known velocity profile done by Ansar et al. (2002) who solved the inviscid solution, present study considering the main channel can capture further subtle phenomena.

In case study, the flows in the intake pipe are numerically investigated for various flowrates and modified setups. As for vertical velocity distribution, reverse flow occurs in the region above the throat, but no negative vertical velocity appears in the suction bell. The vorticity distribution indicates that a pair of strong, nearly symmetric swirl exists around the pipe center. Since swirl angle is widely used to evaluate the pump performance in experiment, the approach with numerical results is performed and discuss in this thesis.

摘  要  I
ABSTRACT  III
誌  謝  V
Contents  VI
List of Tables  IX
List of Figures  X
List of Symbols  XVII
Chapter 1 Introduction  1
1-1 Motivation  1
1-2 Literature Review  5
1-2-1 Review of Pump-Sump Flow Problems  6
1-2-2 Review of Experimental Studies  7
1-2-3 Review of Numerical Studies  8
1-2-4 Review of Design Criterion  11
1-3 Scope of Present Study  14
Chapter 2 Methodology  15
2-1 Numerical Model  15
2-2 Governing Equations  16
2-3 Large Eddy Simulation Model  17
2-4 Finite Volume Method  20
2-5 Volume of Fluid  22
2-6 Volume Tracking Algorithm  24
2-7 Projection Method  25
2-8 Computational Cycle  27
2-9 Implementation on Boundary Conditions  28
2-9-1 No-Slip Boundary Condition  28
2-9-2 Inflow and Outflow Boundary Condition  28
2-10 Numerical Stability  28
2-11 Mesh Generation  30
Chapter 3 Model Validation I: A Sump Model with Straight Approaching low  36
3-1 Introduction  36
3-2 Setup Description  37
3-3 Velocity Profiles  43
3-4 Flow Patterns  45
3-5 Vorticity Contour  48
Chapter 4 Model Validation II: Intake Model with Cross Approaching Flow  69
4-1 Introduction  69
4-2 Setup of Present Study  70
4-3 Streamwise Velocity Distribution  76
4-4 Flow Patterns  77
Chapter 5 Case Study on Flows in the Intake Pipe  84
5-1 Layout of Modified SetupsU  85
5-2 Numerical Setup  87
5-3 Vertical Velocity Distribution  88
5-3-1 Comparisons between Different Discharges  88
5-3-2 Comparisons between Different Modified Setups  90
5-4 Fluid Dynamics in the Intake Pipe  100
5-4-1 Vorticity Contour  100
5-4-2 Circulation Distribution  103
5-4-3 Swirl Angle Approach  104
Chapter 6 Conclusions and Future Works  117
References  118
Appendix A  124
Appendix B  129

                                    

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