Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/1703
標題: 運用小波方法分析並列雙圓柱尾流的長時間特性
Wavelet Analysis on Long Time Characteristic of Wake Flow behind Two Side-by-Side Circular Cylinders
作者: 李宜儒
Li, Yi-Ru
關鍵字: side-by-side circular cylinders;並列雙圓柱;gap flow;intermittent switching, in-phase;anti-phase;double lock-on.;間隙流;間歇性的搖擺;同相位渦漩脫離;異相位渦漩脫離;雙鎖定
出版社: 機械工程學系所
引用: [1]Bearman, P. W., and Davies, M.E., “The Flow about Oscillating Bluff Structures” Proc. 4th Int.Conf. Wind Eff. Bulid. Struct.,ed. K. J. Eation, Cambridge Univ. Press., 1975, pp.285-295. [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 Oscillation”, Journal of Fluid Mechanics, 1991, vol.231, pp.481-499. [3]Hall, M.S., and Griffin, O.M., “Review-Vortex Shedding Lock-on and Flow Control in Bluff Body”, Journal of Fluid Engineering,1991, vol.113, pp.526-537. [4]Ikemoto, K., and Nagaya, K.,“Vortex Shedding Resonance from a Rotational Oscillating Cylinder”, Journal of Fluids and Structures, 1998, vol.12, pp.1041-1053. [5]Kim, H.J., and Durbin P.A., “Investigation of the Flow between a Pair of Circular Cylinders in the Flooping Regime”, Journal of Fluids Mechanics, 1988, vol.196, pp.431-448. [6]Kiya, M., Arie, M., Tamura, H., and Mori, H., “Votex Shedding from Two Circular Cylinders in Staggered Arrangement”, ASME Journal of Fluids Engineering, vol.102, 1980, pp.166-173. [7]Mahbub Alam, Md., Moriya, M., and Sakamto, H., “Aerodynamic Characteristics of Two Side-by-Side Circular Cylinders and Application of Wavelet Analysis on the Switching Phenomenon”, Journal of Fluids and Structures, 2003, vol.18, pp.325-346. [8]Mahir, N., and Rockwell, D., “Vortex Formation From a Forced System of Two Cylinders”, Journal of Fluids and Structures, 1996, vol.10, pp.491-500. [9]Ongoren, A., and Rockwell, D., “Flow Structure from Oscillating Cylinder. Part II:Model Competition in the Near Wake”, Journal of Fluid Mechanics, 1988, vol.191, pp.225-245. [10]Spivack, H.M., “Vortex Frequency and Flow Pattern in the Wake of Two Parallel Cylinders at Varied Spacing Normal to an Air Stream”, Journal of the Aeronautical Sciences, 1946, vol.13, pp.289-297. [11]Sumner, D., Wong, S.T., Price S. J., and Païdoussis, M. P., “Fluid Behavior of Side-by-Side Circular Cylinder in Steady Cross Flow”, Journal of Fluids and Structures, 1999, vol.13, pp.309-338. [12]Wang, Z.J., and Zhou, Y., “Vortex Interactions in a Two Side-by-Side cylinder Near-Wake”, International Journal of Heat and Fluid Flow, 2005, vol.26, pp362- 377. [13]Zdravkovich, M.M., “Review of Flow Interference between Two Circular Cylinder in Various Arrangements”, Journal of Fluid Engineering , 1977, Vol.99, pp.618-633. [14]林呈, “定溫式熱膜流速儀之量測原理及檢定曲線之探討 (一)”, 1986. [15]顏光輝, “二維並列雙圓柱尾流流場特性之探討”, 國立中興 大學土木研究所碩士論文, 1994. [16]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, pp.487-523, 1995. [17]林呈, 顏光輝, “應用流場可視化法探討並列雙圓柱尾流場之 特性研究”, 中國土木水利學刊, vol.2, pp.151-160, 1996. [18]周士欽, “具不同直徑與淨間距之並列雙圓柱尾流鎖定特性之 研究”, 國立中興大學機械研究所碩士論文, 2001. [19]陳信安, “以小波方法分析並列雙圓柱尾流場鎖定特性”, 國 立中興大學機械研究所碩士論文, 2004. [20]楊婷勻, “應用小波轉換法探討並列鈍體間隙流不穩定搖擺之 特性”, 國立中興大學土木研究所碩士論文, 2004.
摘要: 
本文主旨在於研究具不同淨間距、不同直徑比的並列雙柱下游尾流場的長時間特性,並針對間隙流不穩定搖擺的特性、渦漩脫離的相位特性、外加擾動對於並列雙柱尾流結構被鎖定的影響等主題作探討。本實驗於低速循環迴路式的水槽中進行,以螢光染液可視化來觀察並列雙圓柱近域尾流場結構的變化。並使用雷射都卜勒測速儀進行定量流場量測,或搭配熱膜測速儀來進行同步量測。最後將速度訊號運用小波轉換法,藉以瞭解上、下圓柱尾流場的瞬時頻率變化。經長時間的量化統計,結果如下:
(A)等直徑的並列雙圓柱
1.Re=2000、淨間距比為G/D1=1.0〜1.5及Re=5000、淨間距比為 G/D1=0.75〜1.0的條件下,並列雙圓柱之間隙流會呈現間歇性的搖擺。隨著淨間距的增大,寬、窄域尾流交替轉換的頻繁性會增加,不過在大部份的時段內,仍以穩定偏向其中一側的機率為最高。
2.當Re=2000、G/D1≧2.0以及Re=5000、G/D1≧1.25時,並列雙圓柱的間隙流穩定地偏向水平角度。經由長時間統計同(異)相位渦漩離的特性:(1)隨著淨間距的變大,並列雙圓柱尾流渦漩為異相位脫離的機率逐漸變低,而同相位脫離的機率逐漸變高。直到G/D1=5.0(Re=2000),G/D1=4.0(Re=5000),兩者皆往10~20%來靠近。(2)當Re=2000與5000、G/D1≧5.0時,絕大部份則以既非同相位亦非異相位者的機率為最高。
(B)不等直徑的並列雙圓柱
1.當D1=2D2、G/D1=0.75、Re=2000且無因次擾動振幅0.16448,並列雙圓柱受到不同頻率的外加擾動時,其結果為:(1)因為未施加擾動時的窄、寬域尾流的特徵頻率比值fn/fw=3.3,故當大圓柱受到外加擾動時,擾動頻率在3倍的單一大圓柱自然脫離頻率附近(fe/fos=3.03〜3.18)時,寬、窄域尾流具有雙鎖定特性。(2)當大、小圓柱各自受到外加擾動頻率接近各別單一圓柱自然脫離頻率附近(fe/fos=0.970〜1.02與0.848〜0.884)時,寬、窄域尾流也具有雙鎖定特性(3)但整體而論,大圓柱的激擾對窄域尾流的影響較顯著;但小圓柱的激擾對寬域尾流的影響不顯著。

This study investigates the long time characteristics of wake flow behind two side-by-side circular cylinders with different diameter ratios and at various net gaps. The switching characteristics of gap-flow, the phase characteristics of vortex structures and the locked-on characteristics of wakes flow will be emphasized. The experiments are performed in a low-speed recirculation water channel. Qualitative flow visualization and quantitative velocity measurements were performed by way of the laser sheet technique and the FLDV system, respectively. To acquire the phase information, the two velocity signals from FLDV and hot-film anemometer were taken simultaneously and analyzed by cross Wavelet transformation. In the following, some important results are concluded:
(A)Cylinders with equal diameters
1.For the cases, Re=2000, G/D1=1.0〜1.5 and Re=5000, G/D1=0.75〜1.0, the gap-flow between two side-by-side circular cylinders switches intermittently. When the net gap ratio increases, the probability of the switching gap flow increases largely. However, the stably biased gap flow still occupies the most significant portion of the detecting time.
2.For the cases, Re=2000, G/D1≧2.0 and Re=5000、G/D1≧1.25, the gap flow becomes nearly parallel to the free-stream flow during most of the detecting time.(1)When the net gap ratio increases, the probability of the anti-phase vortex shedding decreases and the probability of the in-phase vortex shedding increases. Both of them approaches 10~20% till the net gap ratio is equal to 5(Re=2000)or equal to 4(Re=5000).(2)For the cases, Re=2000 and 5000, G/D1≧5.0, the flow patterns, in form of neither anti-phase shedding nor in-phase shedding, occur most frequently.
(B)Cylinders with unequal diameters
1.For the case,D1=2D2、G/D1=0.75、Re=2000, the following results will be summarized:(1)The ratio of the characteristic frequencies of the narrow and the wide wakes equals 3.3(fn/fw=3.3)in case of no perturbation. When the large cylinder is perturbed at various excitation frequency, the bandwidth of double lock-on for both wakes occurs within the region fe/fos=3.03〜3.18, indicating a subharmonic resonance.(2)When the large and the small cylinder are perturbed separately at various excitation frequencies, the double lock-on bandwidth of both wakes is located at fe/fos=0.970〜1.02 and 0.848〜0.884, respectively.(3)Perturbations on the large cylinder can influence the narrow wake more efficiently. But perturbations on the small cylinder affect the wide wake more insignificantly.
URI: http://hdl.handle.net/11455/1703
其他識別: U0005-2508200614341100
Appears in Collections:機械工程學系所

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