本研究以實際量測流場的方式，分析透水性筐網圓柱周圍及其後方流場之特性，包括水深平均速度場分佈、流速時序性分佈及流場擾動程度等，並探討筐網圓柱物理參數(直徑、表面空隙比)對流場結構之影響。經由實驗結果與相關理論驗證得知，水流通過筐網圓柱後，流速將因筐網圓柱的遮蔽效應而降低。另外，流入結構物內部而抵達柱體後方之穿越流具有穩定流場的特性，故於筐網圓柱後方會形成一流況穩定之低流速區域，稱為「穩定低速區」。
　　在本試驗條件下(平均來流速度27.2cm/sec；平均水深14cm)，筐網圓柱之表面空隙比為主控流場的要素，其影響流場結構的程度高於直徑變化對流場之影響。當筐網圓柱表面空隙比愈大時，透水程度將會愈高而使得穿越流愈強，故其流場將愈穩定。然而，此時柱後流速將因結構物之遮蔽效應減弱而提高。
　　筐網圓柱後方會形成穩定低速區域，而柱體兩側則為紊亂的流速超射區，利用此種流場特性而將筐網圓柱應用於河渠導流或橋墩沖刷防治應可獲得良好成效。

註：
1.表面空隙比：筐網圓柱表面孔洞之總面積與圓柱總表面積之比。
2.穿越流：流經透水構造物內部而抵達結構物後方之水流稱之。

　　This study uses the measurement of flow-field to analyze the characteristics of the fluid around and behind a permeable porous cylinder, such as depth-averaged velocity distribution, time sequence analysis of velocity and disturbance level. The relation between flow structure and physical parameters of porous cylinder, including diameter and void proportion, is investigated.According to the experiment results and the confirmation of related researches, flow velocity decreases after running through the porous cylinder because of the shelter effect. The “bleed flow,” which goes through inner structure and reaches the backward of porous cylinder, has the function to steady flow-field, so there is a steady and low-velocity area behind the porous cylinder, called “steady low-velocity area.”
　　On the same experimental condition (the averaged flow-velocity is 27.2 cm/sec, the averaged flow depth is 14 cm), void proportion is a major factor to flow-field. The influence on the flow-field of void proportion is more than the one of porous cylinder diameter. If the void proportion of porous cylinder is bigger, the permeability will be higher and the bleed flow will become stronger. Therefore, the flow-field will be steadier. However, the flow velocity will become higher because of the decrease of shelter effect.
　　The steady low-velocity area develops behind a porous cylinder, but the both sides of cylinder are turbulent exceeding-velocity zones. To take advantage of this velocity distribution type, using porous cylinder as flow diversion and pier-scour countermeasure could get an excellent result.

1.　Adaramola, M. S., Akinlade, O. G., Sumner, D., Bergstrom, D. J. and Schenstead, A. J., “Turbulent wake of a finite circular cylinder of small aspect ratio,” Journal of Fluids and Structures 22, pp.919 -928, 2006.
2.　Akilli, H. and Rockwell, D., “Vortex formation from a cylinder in shallow water,” Physics of Fluids, Volume 14, Number 9, pp.2957 -2967, 2002.
3.　Allen, D. W. and Henning, D. L., “Vortex-induced vibration current tank tests of two equal-diameter cylinders in tandem,” Journal of Fluids and Structures 17, pp.767-781, 2002.
4.　Baker, C. J., “The Laminar Horseshoe Vortex,” Journal of Fluid Mech., Volume 95, part 2, pp.347-367, 1979.
5.　Besir Sahin, N. Adil Ozturk and Hüseyin Akilli, “Horseshoe vortex system in the vicinity of the vertical cylinder mounted on a flat plate,” Flow Measurement and Instrumentation, 10.1016/ j.flowmeasinst.12.002, 2006.
6.　Bhattacharyya, S., Dhinakaran, S. and Khalili, A., “Fluid motion around and through a porous cylinder,” Chemical Engineering Science 61, pp.4451-4461, 2006.
7.　Daoyi Chen and Gerhard H. Jirka, “Experimental study of plane turbulent wakes in a shallow water layer,” Fluid Dynamics 16, pp. 11-41, 1995.
8.　Edimilson J. Braga and Marcelo J.S. de Lemos, “Simulation of turbulent natural convection in a porous cylindrical annulus using a macroscopic two-equation model,” International Journal of Heat and Mass Tranfer 49, pp.4340-4351, 2006.
9.　Fransson, J. H. M., Konieczny, P. and Alfredsson, P. H., “Flow around a porous cylinder subject to continuous suction or blowing,” Journal of Fluids and Structures 19, pp.1031-1048, 2004.
10.　Gabbai, R. D. and Benaroya, H., “An overview of modeling and experiments of vortex-induced vibration of circular cylinders,” Journal of Sound and Vibration 282, pp.575-616, 2005.
11.　Kawaji, Y. and Ikemoto, K., “Feedback control of vortex shedding from a circular cylinder by rotational oscillations,” Journal of Fluids and Structures 15, pp.23-37, 2001.
12.　Kim, T., Hodson, H. P. and Lu, T. J., “Contribution of vortex structures and flow separation to local and overall pressure and heat transfer characteristics in an ultralightweight,” International Journal of Heat and Mass Transfer 48, pp.4243-4264, 2005.
13.　Kiya, M. and Matsunura, M., “Incoherent turbulence structure in the near wake of a normal plate,” Journal of Fluid Mech., Vol. 190, pp. 343-356.
14.　Konstantinos Marakkos and John T. Turner, “Vortex generation in the cross-flow around a cylinder attached to an end-wall,” Optics & Laser Technology 38, pp.277-285, 2006.
15.　Laura Zima and Norbert L. Ackermann, “Wave Generation in Open Channels by Vortex Shedding from Channel Obstructions,” Journal of Hydraulic Engineering 128:6, pp.596-603, 2002.
16.　Lienhard, J. h., “Synopsis of Lift, Drag and Vortex Frequency Data for Rigid Circular Cylinders,” Washington State University, College of Engineering, Research Division Bulletin, pp.300, 1966.
17.　Lin, Y., So, R. M. C. and Cui, Z. X., “A finite cantilevered cylinder in a cross-flow,” Journal of Fluids and Structures 20, pp.589-609, 2005.
18.　Marco Vanni, “Creeping flow over spherical permeable aggregates,” Chemical Engineering Science 55, pp.685-698, 2000.
19.　Mathelin, L., Bataille, F. and Lallemand, A., “Near wake of a circular cylinder submitted to blowing - Ⅰ,” International Journal of Heat and Mass Transfer 44, pp.3701-3708, 2000.
20.　Mathelin, L., Bataille, F. and Lallemand, A., “Near wake of a circular cylinder submitted to blowing - Ⅱ,” International Journal of Heat and Mass Transfer 44, pp.3709-3719, 2000.
21.　Mathelin, L., Bataille, F. and Lallemand, A., “The effect of uniform blowing on the flow past a circular cylinder,” Journal of Fluids Engineering 124 (2), pp.452–464, 2002.
22.　Muammer Ozgoren, “Flow structure in the downstream of square and circular cylinders,” Flow Measurement and Instrumentaion 17, pp.225-235, 2005.
23.　Munshi, S. R. and Modi, V. J., “Aerodynamics and dynamics of rectangular prisms with momentum injection,” Journal of Fluids and Structures 11, pp.873-892, 1997.
24.　Norberg, C., “Fluctuating lift on a circular cylinder: review and new measurements,” Journal of Fluids and Structures 17, pp.57-96, 2003.
25.　Roger L Simpson, “Junction Flows,” Fluid Mech., 33:415-443, 2001.
26.　Sahin, B., Akkoca, A., Öztürk, N. A. and Akilli, H., “Investigations of flow characteristics in a plate fkin and tube heat exchanger model composed of single cylinder,” International Journal of Heat and Fluid Flow 27, pp.522-530, 2006.
27.　Sobera, M. P., Klijn, C. R. and Van den Akker, H. E. A., “Subcritical flow past a circular cylinder surrounded by a porous layer,” Physics of Fluids 18, 038106, pp.1-4, 2006.
28.　Strouhal, V., “Uber enie Besondere Art der Tonerregung,” Annalen der Physik und Chemie(Leipzig), pp.217-251, 1878.
29.　Von Karman, T., “Uber den Mechanismuss des Windersstandes den ein bewegter Korper in einen Flussigkeit Erfahart,” Nachrichten der k. Gesellschaft der Wissenschaften zu Gottingen, pp.547-556, 1912.
30.　Wang, H. F., Zhou, Y., Chan, C. K. and Lam, K. S., “Effect of initial conditions on interaction between a boundary layer and a wall-mounted finite-length-cylinder wake,” Physics of Fluids 18, 065106, pp.1-12, 2006.
31.　Wontae Kim, Jung Yul Yoo, and Jaeyong Sung, “Dynamics of vortex lock-on in a perturbed cylinder wake,” Physics of Fluids 18, 074103, pp.1-22, 2006.
32.　Xie, O. and Wroblewski, D., “Effect of periodic unsteadiness on heat transfer in a turbulent boundary layer downstream of a cylinder-wall junction,” Int. J. Heat and Fluid Flow 18, pp.107-115, 1997.
33.　Zhang, H. J., Zhou, Y. and Antonia, R. A., “Longitudinal and spanwise vortical structures in a turbulent near wake,” Physics of Fluids, Volume 12, Number 11, 2000.
34.　田中周治、村田暹 ，「計算機援用可視化法による圓柱の後流構造研究」，日本機械學會論文集(B編)，第50卷A58號，pp.2563-2570，1985。
35.　李維人 ，「水中圓柱體振動受力之研究」，第八屆水利工程研討會論文，頁1251~1258，1996。
36.　何宗浚 ，「應用PIV與FLDV於低雷諾數下鈍形體來流端穩態馬蹄型渦流特性之探討」，中興大學土木工程研究所碩士論文，2000。
37.　吳虹邑 ，「筐網結構物對橋墩沖刷保護之研究」，成功大學水利及海洋工程研究所碩士論文，2005。
38.　林呈、謝世圳 ，「應用PIV與FLDV同步量測技術於單圓柱尾流流場之特性探討」，第十三屆水利工程研究會論文，頁M45~M52，2002。
39.　柯亭帆、林正祥、吳志興 ，「亂流通過不同迎面角度方形柱周圍流場之分析」，第八屆水利工程研討會論文，頁297~304，1996。
40.　洪勝榮、張三郎、黃進坤、洪丕振、徐立昌 ，「筐網結構物對凹岸沖刷保護現地測試探討」，水利，第16期，頁97~103，2006。
41.　徐華勇 ，「應用PIV探討圓柱及平版尾流流場之速度分佈特性」，中興大學土木工程研究所碩士論文，2002。
42.　黃進坤 ，「橋墩保護新工法之研究」，台灣公路工程，第32卷第8期，頁39-44，2006。
43.　傅家揚 ，「筐網結構物在不同水流攻角對橋墩沖刷保護之影響」，成功大學水利及海洋工程研究所碩士論文，2006。