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研究生:周士欽
研究生(外文):CHOU SHIH CHIN
論文名稱:具不同直徑與淨間距之並列雙圓柱尾流鎖定特性之研究
論文名稱(外文):Lock on Characteristics of Wake behind Two Side by Side Circular Cylinders with Different Diameters and Various Gaps
指導教授:郭正雄郭正雄引用關係
指導教授(外文):KUO CHENG HSIUNG
學位類別:碩士
校院名稱:國立中興大學
系所名稱:機械工程學系
學門:工程學門
學類:機械工程學類
論文種類:學術論文
論文出版年:2001
畢業學年度:90
語文別:中文
論文頁數:119
中文關鍵詞:鎖定雙鎖定異相位同相位並列圓柱
外文關鍵詞:lock-ondouble lock-onanti-phasein-phaseside-by-side cylinder
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摘 要
本文係以實驗方法研究具有不同直徑、不同淨間距的並列雙圓柱下游尾流被鎖定之特性,藉以瞭解外加擾動的頻率與振幅的變化,對於並列雙圓柱下游尾流結構被鎖定的影響。本文的實驗是在低速循環迴路式的水槽中進行,以螢光染液釋放法紀錄流場可視化,以瞭解並列雙圓柱近域尾流定性演化的情形,並佐以雷射都普勒測速儀系統進行定量流場量測。
本研究的主要內容分為:(1)固定切線速度擾動振幅,變化淨間距以及外加擾動頻率,探討具有相同直徑(D1/D2=1)的並列雙圓柱下游尾流被鎖定的特性。(2)當淨間距G/D2=1時,探討切線速度擾動振幅與頻率變化時,對具有相同直徑(D1/D2=1)的並列雙圓柱下游尾流被鎖定的特性。(3)固定切線速度擾動振幅時,探討淨間距以及外加擾動頻率變化,對具有不同直徑比(D1/D2=1/2)的並列雙圓柱下游尾流被鎖定的特性。
當具有相同直徑之並列雙圓柱下游的尾流受到外加擾動影響時,其結果顯示:(1)隨著兩圓柱的淨間距增大時,並列雙圓柱下游的寬、窄域尾流被鎖定區域的頻寬皆有縮小的現象,同時兩者的鎖定頻段均往單一圓柱特徵頻率(fe*=1)的方向偏移,最後並匯合在一起;(2)當外加擾動頻率接近單一圓柱特徵頻率時,並列雙圓柱下游的寬、窄域尾流結構具有雙鎖定的特性。此時,並列雙圓柱下游的渦流結構具有同相位或異相位交互脫離的現象。(3)當淨間距為G/D2=1時,並列雙圓柱下游寬、窄域尾流被鎖定的範圍,隨著外加擾動振幅持續增大,而有向兩側擴張的趨勢,同時兩個鎖定區域均往單一圓柱之特徵頻率方向匯合。在寬、窄域尾流同時被鎖範圍的重疊區域內,並列雙圓柱下游的尾流具有雙鎖定的現象。(4)當外加擾動頻率接近未擾動前並列雙圓柱下游之寬、窄域尾流特徵頻率時,具有不同直徑比的並列雙圓柱下游的寬、窄域尾流通常會被鎖定。
Abstract
The present investigation is to study the lock-on characteristics of wakes behind two side-by-side circular cylinders with different diameters and various gaps. Quantitative velocity measurements and qualitative dye flow visualization were performed by way of the LDA system and the laser sheet technique, respectively.
Three aspects are investigated in this study: (1) the lock-on characteristics of the wakes behind two side-by-side circular cylinders as functions of excitation frequency and the net gap ratios when excitation amplitude is held constant. (2) the lock-on characteristics as functions of excitation frequencies and amplitudes while the net gap ratio is kept constant at G/D2=1. (3) the lock-on characteristics of two side-by-side circular cylinders with the different diameter(D1/D2=1/2), as functions of excitation frequencies and the net gap ratios.
It is found that (1) when the net gap ratio increases, the lock-on band of the narrow and wide wakes behind each cylinder shrink in bandwidth and tend to shift towards the characteristic frequency of a single circular cylinder(fe*=1). (2) When the excitation frequency approaches fe*=1, both the wakes behind two circular cylinders are locked at the excitation frequency. This is called double lock-on phenomena. When double lock-on characteristic occurs, the flow patterns exhibit either anti-phase or in-phase shedding that appears at random time interval. (3) when the net gap ratio is kept at G/D2=1, the lock-on bandwidth of both narrow and wide wakes become widened with increasing excitation amplitudes. Within the overlapped region of the each lock-on bandwidth, double characteristics of of both narrow and wide wakes occur. (4) When the diameter ratio of two side-by-side circular cylinders becomes unequal (D1/D2=1/2), the lock-on characteristics of either the narrow or the wide wake occurs while the excitation frequency approaches the characteristics frequency of either wake (narrow or wide) behind two side-by-side cylinders.
目 錄
符 號 說 明.....................................................................................1
無因次符號說明..................................................................................2
希臘符號: .....................................................................................2
圖 表 目 錄 ....................................................................................6
第一章 緒 論 .................................................................................11
1-1 研究目的 ...................................................................................11
1-2 文獻回顧 ...................................................................................12
1-3 本文結構 ...................................................................................17
第二章 實驗設備與模型 ..........................................................................18
2-1 循環式水槽 .................................................................................18
2-2 速度量測系統 ...............................................................................19
2-3 圓柱振盪系統 ...............................................................................19
2-4 模型製作 ...................................................................................20
2-4-1 實驗模型系統配置 .........................................................................20
2-4-2 圓柱模型的裝配 ...........................................................................20
第三章 實驗方法及步驟 ..........................................................................22
3-1 流場可視化 .................................................................................22
3-2 FLDV速度量測 ...............................................................................23
第四章 實驗結果與討論 ..........................................................................26
(A) 相等直徑的並列雙圓柱 .....................................................................26
4-1流場可視化定性結果 ..........................................................................26
4-1-1 淨間距為G/ D2=1/2時,並列雙圓柱近域尾流結構.............................................26
4-1-2 淨間距為G /D2=1時,並列雙圓柱近域尾流結構 ..............................................28
4-1-3 淨間距為G/ D2=2時,並列雙圓柱近域尾流結構 ..............................................30
4-1-4 淨間距變化時,寬、窄域尾流結構可視化小結 ................................................31
4-2淨間距變化,流場定量量測結果 ................................................................33
4-2-1 淨間距為G/D2=1/4時,並列雙圓柱近域尾流結構 .............................................33
4-2-2 淨間距為G/D2=1/2時,並列雙圓柱近域尾流結構 .............................................34
4-2-3 淨間距為G/D2=1時,並列雙圓柱近域尾流結構 ...............................................35
4-2-4 淨間距為G/D2=1.22時,並列雙圓柱近域尾流結構 ............................................36
4-2-5 淨間距為G/D2=2時,並列雙圓柱近域尾流結構 ...............................................37
4-2-6 淨間距變化,固定切線擾動量,並列雙圓柱近域尾流場鎖定特性之小結 ..........................39
4-3淨間距G/D2=1時,切線擾動量變化流場量測定量結果 .............................................40
(B)直徑比為1:2的並列雙圓柱 ..................................................................43
4-4流場可視化定性結果討論 ......................................................................43
4-4-1 淨間距為G/D2=1/4時,並列雙圓柱近域尾流結構 .............................................43
4-4-2 淨間距為G/D2=3/4時,並列雙圓柱近域尾流結構 .............................................44
4-4-3 具有不同直徑的並列雙圓柱下游流場可視化小結 ..............................................46
4-5流場定量量測結果 ............................................................................48
4-5-1 淨間距為G/D2=1/4時,並列雙圓柱近域尾流結構 .............................................48
4-5-2 淨間距為G/D2=3/4時,並列雙圓柱近域尾流結構 .............................................50
第五章 結 論 ..............................................................................53
第六章 建議與未來發展方向 ...................................................................55
參 考 文 獻 ....................................................................................56
參 考 文 獻
1.Bearman, P.W., and Wadcock, A.J., ”The Interaction between A Pair of Circular Cylinders Normal to A Stream”, Journal of Fluid Mechanics, vol. 61, 1973, pp. 499-511.
2.Filler, J.R., Marston, P.L., and Mih, W.C., “Response of The Shear Layers Separating from A Circular Cylinder to Small-Amplitude Rotational Oscillations”, Journal of Fluid Mechanics, vol. 231, 1991, pp. 481-499.
3.Hall, M.S., Griffin, O.M., “Vortex Shedding and Lock-on in A Perturbed Flow”, Journal of Fluid Engineering, vol. 115, 1993, pp. 283-291.
4.Hall, M.S., Griffin, O.M., “Review-Vortex Shedding Lock-On and Flow Control in Bluff Body Wakes”, Journal of Fluid Engineering, vol. 113, 1991, pp. 526-537.
5.Mahir, N., and Rockwell, D., “Vortex Formation From a Forced System of Two Cylinders”, Journal of Fluids and Structures, vol. 10, 1996, pp. 491-500.
6.Miau, J. J.,Wang,G. Y.,Chou,J. H., “Intermittent Switching of Gap Flow Downstream of Two Flat Plates Arranged Side By Side”, Journal of Fluids and Structures, vol. 6, 1992, pp. 563-582.
7.Zdravkovich, M.M.., “Review-Review of Flow Interference Between Two Circular Cylinders in Various Arrangements”, Journal of Fluid Engineering, vol. 99, 1977, pp. 618-633.
8.顏光輝, “二維並列雙圓柱尾流流場特性之探討”, 國立中興大學土木工程研究所碩士論文, 1993.
9.張志偉,”具有上蓋平板之空穴內振盪流場之探討”, 國立中興大學機械研究所碩士論文, 1994.
10.林呈, 顏光輝, 郭正雄, “臨界淨間距比條件下並列雙圓柱尾流場特性之實驗研究-雷諾數效應之影響”, 中國土木水利學刊, vol. 4, 1995, pp. 487-523.
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