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Study on Wake and Lock on Characteristics behind Staggered Cylinders of Diameter Ratio Two at Large Gap Ratio
|關鍵字:||大間距;large gap ratio;錯列雙圓柱;頻譜能量;staggered cylinders;spectral energy||出版社:||機械工程學系所||引用:||參考文獻 1.Kiya, M., Vortex shedding from two circular cylinders in staggeed arrangement. Journal of Fluids Engineering, Transactions of the ASME, 1980, 102, pp. 166-173 2.Bloor, M. S., The transition to turbulence in the wake of a circular cylinder. Journal of Fluid Mechanics, 1964. 19, pp. 290-304. 3.Ko, N. W. M., Wong, P. T. Y., and Leung, R. C. K., Interaction of flow structures within bistable flow behind two circular cylinders of different diameters.Experimental Thermal and Fluid Science, 1996, 12, pp. 33-44 4.Lin.J.-C., Rockwell,D.,Quantitative interpretation of vortices from a cylinder oscillating in quiescent fluid.Experiments in Fluids 1997,99-104 5.Baek, S. J.and Sung Hyung Jin, Quasi-periodicity in the wake of a rotationally oscillating cylinder. Journal of Fluid Mechanics,2000,vol408,pp275-300 6.Baek, S. J., and Lee, S. B., and Sung, H. J., Response of a circular cylinder wake to superharmonic excitation. Journal of Fluid Mechanics, 2001, 442, pp. 67-88 7.Choi Sungho,and Haecheon Choi, Characteristics of flow over a rotationally oscillating cylinder at low Reynolds number.Physics of fluids,2002,vol 14,8 8.Lu, X. Y., Numerical study of the flow behind a rotary oscillating circular cylinder. International Journal of Computational Fluid Dynamics, 2002, 16, pp. 65-82 9.Xu, S. J., Zhou, Y., and So, R. M. C., Reynolds number effects on the flow structure behind two side-by-side cylinder. Physics of Fluids, 2003, 15, pp. 1214-1219 10.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. 26, pp. 362-377. 11.Liu Kun,MA,SUN,andYIN, Wake patterns of flow past a pair of circular cylinders in side-by-side arrangments at low Reynolds numbers.Journal of Hydrodynamics,2007,19,pp690-697. 12.Sumner, D., Richards, M. D., and Akosile, O. O., Strouhal number data for two staggered circular cylinders. Journal of Wind Engineering and Industrial Aerodynamics, 2008. 96, pp. 856-871. 13.Lee, S. J.,and Lee, J. Y., PIV measurements of the wake behind a rotationally oscillating circular cylinder, Journal of Fluids and Structures, 2008, 24, pp. 2-17 14.Zheng Z.C.,Frequency effects on lift and drag for flow past an oscillating cylinder. Journal of Fluids and Structures,2008,pp392-399 15.Gao Yangyang, Yu Dingyong, Experimental study on the near wake behind two side-by-side cylinders of unequal diameters.Fluid Dynamics Reasearch,2010,42 16.張修豪,具有兩倍直徑比之錯列圓柱下游流場特性之研究,中興大學機械工程系 碩士論文,2010.||摘要:||
本論文探討具兩倍直徑比與大間距之錯列圓柱尾流結構及鎖定特性。實驗皆在低速循環水槽中進行，以流場可視化作定性觀察，利用雷射測速儀以及質點影像測速系統做定量量測。實驗條件如下：雷諾數為1000、直徑比為2、固定圓柱垂直中心間距(T/D=2)，變化水平間距(L/D)。以能量的觀點探討具大間距以及兩倍直徑比之錯列圓柱下游，不同模式間流場特性的變化，研究重點歸納如下。模式1的流場特性:小圓柱下游對應渦漩脫離頻率的頻譜能量比單一小圓柱者高，最大值約佔入流能量總和約5.5%，且大圓柱下游對應渦漩脫離頻率的頻譜能量分布與單一大圓柱者相似，其分布偏向均勻流側，但其最大值約佔入流能量約14%。兩者之能量均隨著水平間距減少而減弱。在過渡區的特性:錯列大、小圓柱下游對應渦漩脫離頻率的頻譜能量均具有最小值，大圓柱約為4%、小圓柱約為1.9%。模式2的流場特性:大圓柱下游的頻譜能量分佈仍偏向均勻流側，但隨著水平中心間距增加，能量分布開始回復到與單一圓柱者相似，且其最大值也逐漸增加至入流能量約9.8%:相反的，小圓柱下游對應渦漩脫離頻率的頻譜能量卻持續減弱。換言之: Mode 1流場中，小圓柱下游對應渦漩脫離頻率的頻譜能量仍較Mode2流場者高。在不同模式流場中，當大圓柱受到一倍及三倍頻的激擾時，鎖定頻段並沒有太大變化，但大、小圓柱尾流被鎖定頻段之相位差確實有變化；當大圓柱被鎖定之後，對應於擾動頻率的頻譜能量佔入流能量之比例皆比未加擾動下高。
This study investigates the wake and lock-on characters behind two staggered cylinders of diameter ratio 2 at large gap ratios. All the experiments are performed in a low-speed recirculation water channel at Reynolds number 1000. Qualitative flow structures and quantitative velocity measurements were obtained by dye flow visualization, the LDV system and the PIV system. From the fluctuating energy viewpoint, some important results are summarized as follows. For Mode 1 flow structures: The spectral energy at vortex shedding frequency behind small cylinder in staggered arrangement is higher than that of a single small cylinder; and the maximum energy is about 5.5% of inflow energy. The spectral energy distribution at vortex shedding frequency behind large cylinder is similar to that of a single large cylinder; but the magnitude on the free stream side is large. The maximum spectral is about 14% of inflow energy. Both the spectral energy become weak as the horizontal spacing reduces. In transition region between modes 1 and 2, the spectral energy behind both staggered cylinders attains the local minimal. For Mode 2 flow structures: The spectral energy distribution at vortex shedding frequency behind large cylinder is still similar to those in Mode 1. While the horizontal spacing increases, the magnitudes of the spectral energy distribution behind large cylinder gradually recover to that behind a single large cylinder (about 9.8% of inflow energy). However, that behind the small cylinder decreases monotonously as the horizontal spacing increases. While the wake of large cylinder experiences the primary and 1/3 sub-harmonic lock-on, the wake of small cylinder is not locked on. The frequency bands of both lock on range didn’t change too much; but the phase shift between the flow structures across the lock-on frequency band indeed varies. The spectral energy behind large cylinder at exciting frequency is higher than that of a single cylinder.
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