| 姓名 |
李文心(Wen-hsin Lee)
查詢紙本館藏 |
畢業系所 |
土木工程學系 |
| 論文名稱 |
二維矩形柱體尾流之數值模擬
(Numerical Simulation of Two-dimensional Rectangular Cylinders)
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| 相關論文 | |
| 檔案 |
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| 摘要(中) |
本研究利用計算流體動力學數值模式，計算靜止及振動二維矩形柱體周圍流場及柱體所受的阻力與升力。紊流流場的計算採用大渦紊流模式，計算結果並與前人的實驗結果驗證、比對。探討在均勻流況中，長寬比L/D = 1, 3, 5, 10矩形柱體，側牆上的再接觸現象與其所受之升力、阻力。結果顯示：長寬比L/D 3才出現再接觸現象，在接近接觸點位置區域會產生一個最大壓力擾動值，往下游逐漸達到一個穩定值，而時間平均壓力係數會隨著柱體長寬比的增加而減小。另外，本研究亦針對L/D = 5的柱體探討邊牆效應對於渦流逸散和再接觸現象的影響，隨著間隙比越小，柱體上下流場不對稱現象越明顯。且因為柱體和邊牆的間隙縮小，通過的流速增大，導致柱體下方壓力減小，故平均升力係數皆增加。接著，研究週期性振動的方柱體(L/D = 1)和矩形柱體(L/D = 10)的阻力和升力係數。結果顯示：當方柱體水平振動，且振動頻率等於渦流逸散頻率時，平均阻力係數和擾動升力係數有最大值;而垂直上下之矩形柱體，振動頻率等於渦流逸散頻率振動，隨著振幅增大，其升力係數也隨之增大。
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| 摘要(英) |
The unsteady forces and wake flows of two-dimensional rectangular cylinders are numerically simulated by using the Computational Fluid Dynamics (CFD) model. The turbulent flow was computed by the Large Eddy Simulation (LES) model, and the Partial Cell Treatment (PCT) was used to handle the moving solid. The aerodynamic forces, and wake flow of stationary cylinders with different aspect ratios L/D = 1, 3, 5, 10 (L is the length of the rectangular cylinder and D is the height of the cylinder) were investigated in details. The results indicated that the distribution of time-average pressure coefficients on the cylinder wall is related to the reattachment phenomenon.
This study also investigated the wall effect on the flow field around a stationary rectangular cylinder L/D = 5. The rectangular cylinder was placed close to a solid wall with different gap ratio. It is found that as the gap ratio S/D (S is the distance from the wall to the lower face of cylinder) decreased, the mean pressure coefficient on upper and lower walls became asymmetric, and the time-averaged lift coefficient increased as the gap ratio decreased.
Finally, the wake flows of oscillating cylinders were simulated by varying oscillation frequency and amplitude, the resulting drag and lift coefficient of the cylinders are analyzed systematically. The numerical results reveal that for square cylinder (L/D = 1), the time-averaged drag and lift coefficient reach maximum value for in-line oscillation when the forced oscillation frequency equal to the vortex shedding frequency (lock-in region). Also, the transversely oscillated cylinder has the maximum drag coefficient in the lock-in region. The rms lift coefficient of rectangular cylinder of aspect ratio L/D = 10 increased as the oscillation amplitude increased.
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| 關鍵字(中) |
★ 阻力和升力係數
★ 大渦紊流模式
★ 邊牆效應
★ 渦流逸散
★ 計算流體動力學 |
關鍵字(英) |
★ Oscillating cylinder
★ Wake flow
★ Drag and lift coefficient
★ Wall effect
★ Large Eddy Simulation
★ Vortex shedding |
| 論文目次 |
Contents
Abstract I
Contents III
Figure Captions IV
Table Captions VII
1. Introduction 1
2. Numerical Method 7
3. Model Verification 16
4. Results and Discussion 19
4.1 Stationary rectangular cylinder 19
4.2 Stationary cylinders of different length 21
4.3 Stationary cylinder with wall effect 22
4.4 Oscillating cylinder 23
5. Conclusions 24
Reference 26
Figures 29
Tables 57
Appendix 62
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| 參考文獻 |
References
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| 指導教授 |
朱佳仁(Chia-Ren Chu)
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審核日期 |
2010-10-26 |
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