近年來，由於氣候變化的影響，極端氣候的現象比過去更為頻繁，如:暴雨、強風、颱風...等，由於考慮到圓柱結構放置在戶外的情況下，我們在設計外型的階段時必須將惡劣氣候的條件考慮進去。因此，對於在大雨影響下柱體尾流情形的數值模擬更為重要且不可忽視。利用商用軟體FLUENT於不同數量和外型的柱體和大雨機制的模擬。
	在此篇論文中，我們首先對於在雷諾數為100和200流體流經單一圓柱後的尾流分離做數值模擬。接下來，在對於雷諾數為200的情況下兩個相同直徑前後串聯的圓柱做模擬。透過成功的模擬前面3個不同的情況，我們對於接下來的研究更有信心。模擬雷諾數為2.5×104~1.0×105的LP-810纜線在大雨下的情形，則是採用FLUENT內二相流(Two-Phase Flow)的DPM模組(Discrete Phase Model)和改變圓柱的表面出糙度來計算空氣動力特性。雖然模擬出的結果和實驗值不完全相同，但是我們成功的模擬出LP-810在晴空狀態及大雨影響下阻力係數的變化趨勢。本研究在對於工業用纜線在側風及大雨影響條件下的空氣動力特性分析是非常有用的。

In recent years, due to the impact of climate changing, the phenomenon of extreme weather is more frequently compared to the past, such as heavy rain, strong wind, typhoon-weather conditions etc. For the cylindrical structure being located outdoors, we must put these severe weather influences into considerations in the stage of geometry design.  Therefore, the importance of numerical simulation for circular cylinder vortex flow under the heavy rain effects can never be neglected. 
	In this work, we first investigated the vortex shedding behind a circular cylinder at Re=100 and 200. Secondly, two circular cylinders in tandem arrangement at Re=200 are simulated also. Through the simulation of these three cases successfully, we will be more confident for the following research. For the heavy rain simulations, the two-phase flow approach plus the wall film mechanism on the body surface are implemented for LP-810 cable and at Re=2.5×104 to 1.0×105. Although the numerical results for the cable under the heavy rain effects show that aerodynamic degradation was not perfectly match to the experimental data, the correct tendency of the cable aerodynamic performance under both the clear weather and heavy rain situations are simulated successfully. The proposed simulation results will be quite useful to understand the industrial suspension cable’s behavior in cross wind and heavy rain conditions.

Contents

Abstract	I
Contents	III
List of Tables	IV
List of Figures	V
Nomenclatures	VII
Chapter 1 Introduction	1
Chapter 2 Research Background	4
Chapter 3 Characteristics of Rain	9
Chapter 4 Numerical Modeling	13
4-1 Geometry Model Construction	13
4-2 Grid Generation	16
4-3 Flow Solver	20
4-4 Turbulence Modeling	23
4-5 Discrete Phase Model	25
4-6 Surface Roughness	29
4-7 Heavy Rain Physics	31
Chapter 5 Results and Discussion	34
Chapter 6 Conclusions	55
References	57

 
List of Tables

Table 5-1 The average drag coefficients and Strouhal number for a single circular cylinder at Re=100 and Re=200 [9]	38
Table 5-2 Numerical results for a single circular of pressure and viscous drag coefficient at Re=100 and 200	39
Table 5-3 The Strouhal number and mean drag coefficients for two circular cylinders in tandem arrangement at Re=200	40
Table 5-4 Numerical results for two circulars of pressure and viscous drag coefficient at Re=200	41
Table 5-5 The drag coefficient of the LP-810 cable for different turbulence models	43
Table 5-6 The comparison of the drag coefficient for the cable and smooth circular cylinder with V=10 m/s and V=40 m/s	46
Table 5-7 Heavy rain conditions	47
Table 5-8 Numerical results for cable LP-810 of drag coefficients degradation percentage	49
Table 5-9 Experiment results for cable LP-810 of drag coefficients degradation percentage [19]	49
Table 5-10 Numerical results for cable LP-810 of viscous drag coefficients degradation percentage	51
Table 5-11 Numerical results for cable LP-810 of pressure drag coefficients degradation percentage	51
 
List of Figures

Figure 2-1 Regimes of fluid flow over a circular cylinder [4]	7
Figure 2-2 Normalized distribution of the total data sample [16]	10
Figure 4-1 Computational domain of a single circular cylinder	14
Figure 4-2 Computational domain of two circular cylinders in tandem arrangement	14
Figure 4-3 The geometric model of cable compared to Kikuchi's Model [19]. (a) Kikuchi's Model (LP-810) and (b) present numerical model	15
Figure 4-4 Computational domain of cable LP-810	15
Figure 4-5 Mesh of the entire calculation domain for a single cylinder	17
Figure 4-6 Near mesh of a single circular cylinder	17
Figure 4-7 Mesh of the entire calculation domain for two cylinders	18
Figure 4-8 Near mesh of the downstream cylinder	18
Figure 4-9 Mesh of the entire calculation domain for cable LP-810	19
Figure 4-10 Near mesh of cable LP-810	19
Figure 4-11 Physics of splashing, momentum, heat, and mass transfer for the Wall-Film [20]	27
Figure 5-1 (a) Vorticity (b) Pressure field at Re=100	35
Figure 5-2 (a) Vorticity (b) Pressure field at Re=200	36
Figure 5-3 Lift and drag coefficient for a single cylinder at Re=100	37
Figure 5-4 Lift and drag coefficient for a single cylinder at Re=200	37
Figure 5-5 Pressure and viscous drag for a single cylinder at Re=100 and 200	38
Figure 5-6 (a) Vorticity and (b) Pressure contours for two circular cylinders in tandem arrangement	40
Figure 5-7 The averaged drag coefficient for LP-810	cable numerical and experimental results..................................................................................42
Figure 5-8 Drag coefficient for cable LP-810 numerical result comparing to experimental data	42
Figure 5-9 Pressure contours for different free stream velocities with LWC=0 g/m3	44
Figure 5-10 Vorticity contours for different free stream velocities with LWC=0 g/m3	45
Figure 5-11 Local view of rain droplets impingement	48
Figure 5-12 Drag coefficient for cable LP-810 numerical and experimental results	50
Figure 5-13 Viscous drag coefficient for different wind speed with LWC=0 g/m3 and LWC=9.23 g/m3	52
Figure 5-14 Pressure drag coefficient for different wind speed with LWC=0 g/m3 and LWC=9.23 g/m3	52
Figure 5-15 Pressure contours for different free stream velocity with LWC=9.23 g/m3	53
Figure 5-16 Vorticity contours for different free stream velocity with LWC=9.23 g/m3	54

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