臺灣博碩士論文加值系統

摘 要

本研究以兩個3 cm x 3 cm之方柱，在直立式水槽中，以縱列方式排列，探討在不同雷諾數、間距比及下游方柱攻角變化下的流場特徵模態、阻力係數及渦漩逸放特性。實驗中先利用流場可視化(partical tracking flow visualization，PTFV) ，觀察流場之特徵模態，從中發現不同雷諾數下，上下游方柱不轉角度時，隨著間距比之變化有三種不同的特徵模態，為單一方柱模態(single mode) 、再回附模態(reattach mode)及跳躍模態(jump mode)；在固定雷諾數下，上游方柱不轉角度，下游方柱轉角度時有三種特徵模態，為模態I、模態II及模態III。並利用質點影像測速儀(particle image velocimetry，PIV)分析得到在不同模態下之速度向量、流線、渦度及渦漩時序，進而得到流場之阻力及渦漩逸放頻率，便可發現各模態之驅勢，並得知無因次化渦漩逸放頻率在以黏滯力主導之流場會呈現隨雷諾數增加而減少;在以慣性力主導之流場會呈現隨雷諾數增加而增加之趨勢。實驗中並搭配臨界點理論之拓樸學(Topology)分析不同之流場模態以印證之前所得到之實驗結果。
關鍵字：雙方柱，流場可視化，質點影像測速儀，渦漩逸放

Abstract

In this research, two 3 cm x 3 cm square cylinders were aligned in a vertical water tank. The flow field characteristic modes, drag coefficients and vortex shedding properties were explored with changing the Reynolds numbers, spacing ratio and downstream cylinder’s angles of attack. Utilizing the particle tracking flow visualization (PTFV) technique was applied to observe the flow fields. The flow field can be classified into three characteristic modes, that is, the single mode, reattach mode and jump mode under the conditions of variable Reynolds number, changeable angles of cylinders and adjustable spacing ratio. Three characteristic modes are classified, that is, mode I, mode II and mode III, under the conditions of fixed Reynolds number, fixed upstream cylinder and angle-adjustable downstream cylinder. The particle image velocimetry (PIV) was applied to analyze the velocity, streamline, vorticity and vortex sequence in different modes. Furthermore, the trend of these modes can be found by the drag and vortex shedding frequency. The results show that, in the viscosity-dominated flow fields, the non-dimensional vortex shedding frequencies decrease when the Reynolds numbers are raised. Additionally, in the inertia-dominated flow fields, the frequencies change coordinately with the Reynolds numbers. The topological analysis was also utilized in this research to verify the experimental results.
Keyword: Twin square cylinders, PTFV, PIV, Vortex shedding

目 錄
頁次
致謝……………………………………………………………….. i

摘要……………………………………………………………….. ii
Abstract……………………………………………………………. iii
目錄……………………………………………………………….. iv

表目錄…………………………………………………………….. vi

圖目錄…………………………………………………………….. vii

符號索引………………………………………………………….. x

第一章 緒論……………………………………………………… 1
1-1 研究動機…………………………………………………. 1
1-2 文獻回顧…………………………………………………. 1
1-3 研究目的…………………………………………………. 4
第二章 研就構思及實驗設備、儀器與方法…………………….. 5
2-1 研就構思…………………………………………………. 5
2-2 實驗設備…………………………………………………. 5
2-2.1 水洞………………………………………………. 5
2-2.2 方柱模型…………………………………………. 6
2-3 實驗儀器及方法………………………………………… 6
2-3.1 流量量測…………………………………………. 6
2-3.2 流場可視化………………………………………. 6
2-3.3 速度場量測………………………………………. 7
2-3.4 雷射光頁…………………………………………. 11
第三章 縱列雙方柱的流場特徵………………………………… 12
3-1 流場的特徵模態…………………………………………. 12
3-2 流場特徵模態之PIV分析………………………………. 14
3-2.1 速度向量場、流線、渦度……………………….. 15
3-2.2 特徵模態的拓樸分析…………………………….. 17
第四章 縱列雙方柱的阻力及渦漩逸放特性…………………… 21
4-1 阻力係數…………………………………………………. 21
4-2 渦漩逸放特性……………………………………………. 21
4-2.1 流場的衍化過程………………………………….. 22
4-2.2 尾流紊流特性的統計分析……………………….. 23
4-2.3 特徵長度尺度…………………………………….. 25
4-2.4 渦漩逸放頻率…………………………………….. 25
第五章 結論與建議……………………………………………… 29
5-1 結論………………………………………………………. 29
5-2 建議………………………………………………………. 30
參考文獻………………………………………………………….. 31
附錄一………………………………………………………….. 36

參考文獻

[1] Rockwell, D. O., “Organized fluctuations due to flow past a square cross section cylinder,” Journal of Fluids Engineering, Vol. 99, pp. 511-516 (1977).
[2] Obasaju, E. D., “An investigation of the effects of incidence on the flow around a square section cylinder,” Aeronautical Quarterly, Vol. 34, pp. 243-259 (1983).
[3] Lyn, D. A., Einav, S., Rodi, W., and Park, J.-H., “A laser-Doppler velocimetry study of the ensemble-averaged characteristics of the turbulent near wake of a square cylinder,” Journal of Fluid Mechanics, Vol. 304, pp. 285-319 (1996).
[4] Dutta, S., Muralidhar, K., and Panigrahi, P. K., “Influence of the orientation of a square cylinder on the wake properties,” Experimental in Fluids, Vol. 34, pp. 16-23 (2003).
[5] Okaijma, A., “Strouhal number of rectangular cylinders,” Journal of Fluid Mechanics, Vol. 123, pp. 379-398 (1982).
[6] Norberg, C., “Flow around rectangular cylinders : pressure forces and wake frequencies,” Journal of Wind Engineering and Industrial Aerodynamics, Vol. 49, pp. 187-196 (1993).
[7] Cheng, M., and Liu, G. R., “Effects of afterbody shape on flow around prismatic cylinders,” Journal of Wind Engineering and Industrial Aerodynamics, Vol. 84, pp. 181-196 (2000).
[8] Zdravkovich, M. M., “Review of interference-induced oscillations of two pararrel circular cylinders in various arrangements,” Journal of Wind Engineering and Industrial Aerodynamics, Vol. 28, pp. 183-200 (1988).
[9] Wong, P. T. Y., Ko, N. W. M., and Chiu, A. Y. W., “Flow characteristics around two parallel adjacent square cylinders of different sizes,” Journal of Wind Engineering and Industrial Aerodynamics, Vol. 54/55, pp. 263-275 (1995).
[10] Kolar, V., Lyn, D. A., and Rodi, W., “Ensemble-averaged measurements in the turbulent near wake of two side-by-side square cylinders,” Journal of Fluid Mechanics, Vol. 346, pp. 201-237 (1997).
[11] Lou, S. C., Li, L. L., and shah, D. A., “Aerodynamics stability of the downstream of two tandem square-section cylinders,” Journal of Wind Engineering and Industrial Aerodynamics, Vol. 79, pp.79-103 (1999).
[12] Kang, S., “Characteristics of flow over two circular cylinders in a side-by-side arrangement at low Reynolds numbers,” The Physics of Fluids, Vol. 15, 9 (2003).
[13] Liu, C. H., and Chen, J. M., “Observations of hysteresis in flow around two square cylinders in a tandem arrangement ” Journal of Wind Engineering and Industrial Aerodynamics, Vol. 90, pp.1019-1050 (2002).
[14] Robichaux, J., Balachandar, S., and Vanka, S. P., “Three-dimensional floquet instability of the wake of square cylinder,” The Physics of Fluids, Vol. 11, 3 (1999).
[15] Richard, C. F., and John, H. S., Fundamental of air pollution engineering,New Jersey, pp.290-357(1988)
[16] Mei, R., “Velocity fidelity of flow tracer particles, “Experimental in Fluids, vol.22,1(1996)
[17] Lighthill, M. J., Laminar boundary layer, Ed. Rosenhead, L., Oxford University, College of Engineer, pp. 44-88 (1963).
[18] Perry, A. E., and Fairlie, B. D., “Critical points in flow patterns,” Advances in Geophysics. B, Vol. 18, pp. 299-315 (1974).
[19] Perry, A. E., Chong, M. S., and Lim, T. T., “The vortex-shedding process behind two-dimensional bluff bodies,” Journal of Fluid Mechanics, Vol. 116, pp. 77-90 (1982).
[20] Perry, A. E., and Steiner, T. R., “Large-scale vortex structures in turbulent wakes behind bluff bodies. Part I, vortex formation process,” Journal of Fluid Mechanics, Vol. 174, pp. 233-270 (1987).
[21] Hunt, J. C. R., Abell, C. J., Peterka, J. A., and Woo, H., “Kinematical studies of the flows around free or surface-mounted obstacles applying topology to flow visualization,” Journal of Fluid Mechanics, Vol. 86, part I, pp. 179-200 (1978).
[22] Coutanceau, M., and Pineau, G., “Some typical mechanisms in the early phase of the vortex-shedding process from particle-streak visualization, Atlas of Visualization III,” Eds. Nakayama, Y. and Tanida, Y., CRC Press, Boca Raton, pp. 43-68 (1997).
[23] Tennekes, H., and Lumley, L., A First Course in Turbulence, MIT Press, Cambridge, 8 (1972).
[24] McGillem, C. D., and Cooper, G. R., Continuous and Discrete Signal and System Analysis, Holt, Rinehart and Winston, New York, 52 (1984).
[25] 李漢文, “紊流對機翼表面流、氣動力性能及尾流區非穩態運動的效應, ”國立台灣科技大學機械工程系博士學位論文(1999)
[26] Roshko, A., “On the development of turbulent wakes from vortex streets,” NACA Report 1911 (1954).