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Study on Flow Characteristics behind Two Staggered Circular Cylinder of Diameter Ratio Two
|關鍵字:||staggered;錯列;bluff body;gap flow;two circular cylinders;鈍體;間隙流;雙圓柱||出版社:||機械工程學系所||引用:||1. Alam, M. M. and Zhou, Y., Strouhal numbers,forces and flow structures around two tandem cylinders of different diameters. Journal of Fluids and Structures, 2008. 24, pp. 505-526. 2. Auteri, F., Belan, M., Gibertini, G., and Grassi, D., Normal flat plates in tandem: An experimental investigation. Journal of Wind Engineering and Industrial Aerodynamics 2008. 96, pp. 872-879. 3. Bloor, M. S., The transition to turbulence in the wake of a circular cylinder. Journal of Fluid Mechanics, 1964. 19, pp. 290-304. 4. Igarashi, T., Characteristics of a flow around two circular cylinders of dofferent diameters arranged in tandem. Bulletin of the JSME, 1982. 25, pp. 349-357. 5. Kiya, M., Vortex shedding from two circular cylinders in staggered arrangement. Journal of Fluids Engineering, Transactions of the ASME, 1980. 102, pp. 166-173. 6. 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. 7. Spivack, H. M., Vortex frequency and flow pattern in the wake of two parallel cylinder at naried spacing normal to an air stream. Aeronautical Sciences, 1946. 13, pp. 289-297. 8. Sumner, D., Price, S. J., PA, Iuml, and DOUSSIS, M. P., Flow-pattern identification for two staggered circular cylinders in cross-flow. Journal of Fluid Mechanics, 2000. 411, pp. 263-303. 9. 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. 10. Sumner, D., Wong, S. S. T., and Price, S. J., Fluid behaviour of side-by-side circular cylinders in steady cross-flow. Journal of Fluids and Structures, 1999. 13, pp. 309-338. 11. 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. 12. 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. 13. Zdravkovich, M. M., Review of flow interference between two circular cylinder in various arrangements.ASME Trans. Journal of Fluid Engineering, 1977. 26, pp. 618-633. 14. Zhou, Y. and Antonia, R. A., Effect of initial condition on structures in a turbulent near-wake. AIAA, 1994, pp. 1207-1213. 15. Zhou, Y. and Antonia, R. A., The effect of Reynolds number on a turbulent far-wake. Experiments in Fluids, 1998. 25, pp. 118-125. 16. ProVISION-XS User Manual, 2007. 17. 李宜儒, 運用小波方法分析並列雙圓柱尾流的長時間特性,中興大學 機械工程系 碩士論文,2006. 18. 廖景晨, 縱列圓柱-垂直平板間自激式振盪流場及下游水平板影響之實驗研究,中興大學 機械工程系 碩士論文,2009.||摘要:||
本論文係研究具有兩倍直徑比之錯列雙圓柱下游流場之特性。雷諾數為1000時，錯列圓柱之中心間距在L/D=-2.0~1.0，T/D=1.0~2.0間變化。本實驗在低速循環式水槽中進行，以流場可視化作定性的觀察，再以雷射都普勒測速儀、質點影像測速系統作定量量測。並且運用小波分析以及環流量之變化，進一步了解具有兩倍直徑比之錯列雙圓柱下游流場之特性。實驗結果顯示：當錯列雙圓柱之中心間距較大時，大、小圓柱下游流場會形成兩對平行流向的渦街結構，其特徵頻率會趨近單一大、小圓柱者。當錯列雙圓柱之中心間距逐漸縮小，因大、小圓柱相對位置之不同，導致間隙流偏斜，形成模式1(Mode 1)與模式2(Mode 2)。當錯列雙圓柱之中心間距持續縮小時，寬域兩側形成剪力層特性，往下游演化過程中，可能會產生渦漩配對，其特徵頻率會逐漸變為近域特徵頻率的 倍，在更下游處則會形成一交替脫離的渦列；而窄域下游尾流則形成交替脫離的渦漩，其特徵頻率為高頻。當錯列雙圓柱之中心間距很小時，圓柱後方為寬域者，其外側之剪力層特性更明顯，僅在下游處形成無渦漩配對低頻的渦漩結構；圓柱後方為窄域者，在下游則先形成尾流特性。因三個渦漩形成的位置相當靠近，且渦漩形成長度很短，尾流特性之範圍很小，往下游演化過程中，陸續結合成一大尺度渦漩，其特徵頻率接近寬域外側剪力層者。在更下游處，與寬域外側之渦漩逐漸形成一個具有低頻的交替脫離渦漩列。
This study investigates the flow characteristics behind two staggered circular cylinders of diameter ratio two by experiment. The Reynolds number was kept 1000; and the streamwise and the transverse distances between the cylinder centers are located within the range of L/D=-2.0~1.0, T/D=1.0~2.0, respectively. All the experiments are performed in a low-speed recirculation water channel. The qualitative flow structures were observed by the dye flow visualization technique, and the quantitative velocity measurements were performed by the FLDV system. Some of the data are analyzed by the cross Wavelet transformation. Further, using the PIV system acquire the instantaneous vorticity and circulation of the related flow structures between these two staggered cylinders. Some important results are summarized as follows: When the distances (either streamwise or transverse) between the centers of staggered circular cylinders are large, the gap flow becomes nearly parallel; and the flow structure forms two parallel vortex streets shed alternatively in the downstream regions. In these cases, the characteristic frequencies are very close to those behind a single large and small circular cylinders. While the center spacing decreases, two modes of the flow structures are defined, mode 1 and 2, depending upon the phases of the gap vortices. At smaller gap, the flow of the narrow wake shows the characteristic with much higher frequency. However, the two outer shear layers of the wide wake sometimes show the pairing of the vortices, forming the 1/2 subharmonic component of the frequency of the narrow wake during the evolution process. In the further downstream region, the wake character may be formed with a low characteristic frequency. Further decrease of the distances (L/D and T/D) between two cylinders much shorter vortex formation length is found behind the narrow wake. On the other hand, the outer shear layers of the wide wake can only form the vortices of much low frequency due to instability. The widely spread shear layer interacts strongly with the vortex street of the narrow wake and will form a much large scale vortex in the farther downstream region. The characteristic frequencies of the two shear layers are close, and may form a vortex street shed alternatively with much lower frequency.
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