Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/2804
標題: 具有小間距的不等直徑錯列圓柱下游流場特性之研究
Study on Flow Characteristics behind Staggered Cylinders of Unequal Diameter at Small Gap
作者: 許尚文
Hsu, Shang-Wen
關鍵字: 間隙流
gap flow
錯列雙圓柱
渦旋
不等直徑
staggered cylinder
vortex
unequal diameter
出版社: 機械工程學系所
引用: 1. Spivack, H.M., Vortex frequency and flow pattern in the wake of two parallel cylinders at varied spacing normal to an airstream, 1945, Catholic University of America. 2. Bloor, M.S., The transition to turbulence in the wake of a circular cylinder. Journal of Fluid Mechanics, 1964. 19(02): p. 290-304. 3. Zdravkovich, M., Review of flow interference between two circular cylinders in various arrangements. ASME Transactions Journal of Fluids Engineering, 1977. 99, p. 618-633. 4. Kiya, M., et al., Vortex shedding from two circular cylinders in staggered arrangement. Journal of Fluids Engineering, 1980. 102: p. 166. 5. Williamson, C. H. K. , Evolution of a single wake behind a pair of bluff bodies. Journal of Fluid Mechanics, 1985. 159, p. 1-18. 6. 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, p. 309-338. 7. Sumner, D., S. Price, and M. Paidoussis, Flow-pattern identification for two staggered circular cylinders in cross-flow. Journal of Fluid Mechanics, 2000. 411(1): p. 263-303. 8. Xu, S., Y. Zhou, and R. So, Reynolds number effects on the flow structure behind two side-by-side cylinders. Physics of Fluids, 2003. 15: p. 1214. 9. Zhao, M., Cheng, L., Teng, B., Liang, D., Numerical simulation of viscous flow psst two circular clinder of different diameters. Applied Ocean Research, 2004. p 1-17 10 Akilli, H., A. Akar, and C. Karakus, Flow characteristics of circular cylinders arranged side-by-side in shallow water. Flow Measurement and Instrumentation, 2004. 15(4): p. 187-197. 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, p. 362-377. 12. Hu, J. and Y. Zhou, Flow structure behind two staggered circular cylinders. Part 1. Downstream evolution and classification. Journal of Fluid Mechanics, 2008. 607: p. 51-80. 13. Gao, Y., et al., Experimental study on the near wake behind two side-by-side cylinders of unequal diameters. Fluid dynamics research, 2010. 42(5): p. 055509. 14. 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, 2005. 15. 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. 16. Roshko, A., On the development of turbulent wakes from vortex streets. 1954.
摘要: 本論文利用質點影像測速系統(PIV)、流場可視化、以及快速傅立葉轉換(FFT)來進行流場結構及特性分析,探討當雷諾數為1000時,具有直徑比為1、2、4之錯列圓柱下游之流場結構及能量消長變化。其中,錯列雙圓柱之垂直間距固定為G/D=0.25,水平間距為L/D=-3.5~3.5。研究結果顯示:在D/d=1時,沒有mode 1和mode 2之分別。當D/d=1、-3.5≦L/D≦-2.0與2.0≦L/D≦3.5均屬於渦旋A+B+C型流場,在更下游處,A、B、C渦旋結合成一大尺度渦旋再脫離。當D/d=1、-2.0<L/D<-0.5與0.5<L/D<2.0均屬於渦旋A+C型流場,C渦旋與窄域A渦旋結合為A+C渦旋並與B渦旋往下游流場移動。當D/d=1、-0.5≦L/D≦0.5,則為窄域尾流被寬域尾流切斷的流場。當直徑不相等且間隙流偏向大圓柱時,此類流場為Mode 1流場;反之間隙流向小圓柱偏擺時,此類流場為Mode 2流場。在Mode 1流場中:D/d=2、-3.5≦L/D<-1.0,D/d=4、-3.5≦L/D<-1.5,寬域C渦旋與窄域A渦旋結合為A+C渦旋,並與B渦旋往下游流場移動;其中,在D/d=2、-3.5≦L/D≦-3.0,D/d=4、-3.5≦L/D<-1.5時,會發生小圓柱尾流被抑制,使得流場中呈現單一頻率。D/d=2、-1.0≦L/D≦1.0,D/d=4、-1.5≦L/D≦0時,窄域尾流在近域中會被寬域尾流切斷,在下游處形成單一卡氏渦街。此類流場結構可分為Mode 1或Mode 2兩種,但均屬於窄域尾流被寬域尾流切斷的流場。在Mode 2流場中:當D/d=2、2.0<L/D≦3.5,D/d=4、3.0<L/D≦3.5屬於間隙流推擠窄域尾流,大、小圓柱下游的A、B與C、D渦旋均交替脫離,但仍受到間隙流之推擠。當D/d=2、1.0<L/D≦2.0,D/d=4、0<L/D≦3.0為間隙流推擠窄域尾流並形成Bn渦旋,流場結構為小圓柱下游的C、D渦旋交替脫離;唯當C渦旋流經B渦旋下方時,會影響B渦旋進而產生Bn渦旋,在更下游處以A、Bn的渦旋交替脫離。
This study investigates the flow characteristics using Particle Image Velocimetry (PIV), Laser Doppler measurement system (LDV), flow visualization and fast Fourier transform (FFT). The Reynolds number is 1000, and the diameter ratios of staggered cylinders are 1.0, 2.0 and 4.0. The staggered cylinders are arranged at same gap ratio (G/D=0.25) with varying horizontal spacing within -3.5≤L/D≤3.5. For D/d=1, the modes 1 and 2 are exact mirror image of each other. For D/d=1, -3.5≦L/D≦-2.0 and 2.0≦L/D≦3.5, the vortices A, B, C merge into a large vortex in the downstream region. For -2.0<L/D<-0.5 and 0.5<L/D<2.0, vortex C will combine with vortex A and merge with B vortex further downstream. For the case of D/d=1, -0.5≦L/D≦0.5, the narrow wake will be terminated by wide wake in the near field. For the case of staggered cylinders of unequal diameter, the flow structures can be divided into two main categories. First, as the gap flow biases toward the large cylinder, it is defined as Mode 1; while the gap flow biases toward the small cylinder, the flow is defined as Mode 2. In the category Mode 1, for D/d=2, -3.5≦L/D<-1.0 and D/d=4, -3.5≦L/D<-1.5, the vortex C of small cylinder (wide wake) and the A vortex of large cylinder (narrow wake) merges and move downstream with B vortex. For D/d=2, -3.5≦L/D≦-3.0 and D/d=4, -3.5≦L/D<-1.5, the wake behind small cylinder is completely suppressed and only a single frequency is detected in the flow field. In both D/d=2, -1.0≦L/D≦1.0 and D/d=4, -1.5≦L/D≦0, the narrow wake is always terminated by the wide wake and may be presented by either Mode 1 or Mode 2. Further, in Mode 2 category, for D/d=2, 2.0<L/D≦3.5 and D/d=4, 3.0<L/D≦3.5, the individual vortex street will shed alternately which are still affected by the biased gap flow. When D/d=2, 1.0<L/D≦2.0 and D/d=4, 0<L/D≦3.0, C, D vortices alternately shed behind the small cylinder. In additions, the successive vortices B from the inner shear layer of the large cylinder are induced by the successive formation of vortices C and D, and merge into a large scale Bn vortex in the downstream region. In the further downstream region, the Bn vortex and A vortex will shed alternatively.
URI: http://hdl.handle.net/11455/2804
其他識別: U0005-2308201311170700
文章連結: http://www.airitilibrary.com/Publication/alDetailedMesh1?DocID=U0005-2308201311170700
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