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  • 學位論文

雙方柱於均勻流下干擾引致雙穩態氣動力現象之探討

Investigation on the interference induced bistable aerodynamic phenomenon of double square prisms under uniform flows

指導教授 : 羅元隆
共同指導教授 : 張正興(Cheng-Hsin Chang)

摘要


隨著社會經濟發展、人口密集,導致建築物高度提升、相互間之距離縮減。而群體型建築物之干擾效應會使流場產生變化,進而改變其氣動力現象。以往,已有許多學者針對三維之雙棟建物進行研究與探討,而由於三維流場之高度複雜性,加上干擾效應之成因為諸多不同因素形成,導致此研究目前仍停留在以實驗數據呈現其結果之階段,無法依照各干擾成因分別獨立探討,且未能與設計風載重之規範進行結合。因此本研究選擇採用以二維方式進行實驗,深入探討風力於雙方柱之相互干擾影響下之變化,及其引致之雙穩態現象。 本研究使用淡江風工程研究中心之橋梁斷面模型風洞,進行雙方柱之氣動力與強制振動實驗,並以壓力量測系統取得雙方柱之風壓數據。以單方柱之氣動力現象做為對照數據,將雙方柱之氣動力現象與其進行比較,觀察當雙方柱改變其之間距離時,其相互間所造成的干擾影響。且特別探討雙方柱於特定間距下所引致的雙穩態現象,主要與Sakamoto(1988)之結論進行驗證與討論。且更透過8%紊流下之雙方柱氣動力實驗,將其現象於不同紊流流場下之變化能更加完整地呈現,初估出雙穩態現象於不同紊流強度下之變化趨勢。 本研究於氣動力實驗之結果顯示,上游方柱會因下游方柱之存在而受抑制,下游方柱則因上游方柱之遮蔽影響,其本身承受之風速偏低於上游方柱。並於紊流強度0.5%下,發現雙穩態現象出現在X⁄D=3.25~3.6之間距內,其兩種流場特性以間歇交替性形式進行轉換,而於8%紊流雖無發現此現象之產生,但其流場則以連續性形式依照相同趨勢轉換其特性。

並列摘要


With the development of the social economy and the density of population, the buildings are raised in height and shortened the distance among each other. The interference effect of structures causes the variation of the flow and in turn, changes the aerodynamic phenomenon. Previously, many academics studied in the interference effect of high-rise buildings. However, the conclusions still stay at the stage that can only show the results of the experiment because of the high complexity of the three-dimensional flow pattern, and the cause of the interference effect is formed by lots of different factors. Therefore, this study will be a two-dimensional experiment to focus on the change of aerodynamic phenomenon under the interference effect of the two square prisms and the bistable phenomenon caused by the specific distance of the prisms. This study does the aerodynamic and forced vibration experiment in Tamkang University Wind Engineering Research Center, and uses Scanvavle to get the prisms' surface pressure. And it compares the experiment results of the isolated prism with the double prisms to observe the interference effect when the distance of the prisms changed. Also, this study discusses the bistable phenomenon at the specific distance of the prisms and verifies with the results of Sakamoto(1988). Then, it does the same aerodynamic experiment at the turbulent intensity of 8%, aims to show the bistable phenomenon of the different turbulent intensity more completely. The results show that the upstream prism is reduced by the presence of the downstream prism. And the velocity of the downstream prism is caused by the blockage of the upstream prism that is lower than the original velocity setting. It finds that under the turbulent intensity of 0.5%, the bistable phenomenon appears at the 3.25 to 3.65 times the distance of the two prisms and that the two different flow patterns switch in an intermittent and alternate form. However, when the turbulent intensity is under 8%, the bistable phenomenon does not occur but the flow pattern is switched in the same trend.

參考文獻


【1】B E Lee, “The effect of turbulence on the surface pressure field of a square prism”, J. Fluid Mech., Vol. 69, part 2, pp. 263~282, 1975.
【2】P W Bearman, D M Trueman, “An investigation of the flow around rectangular cylinders”, The Aeronautical Quarterly, Vol. 13, pp. 229~237, 1972.
【3】Hiroshi Nakaguchi, Kikuhiro Hashimoto, Shinri Muto, “An experimental study on aerodynamic drag of rectangular cylinders”, Japan society of aeronautical engineering, Vol. 16, issue 168, pp. 1~5, 1968.
【4】P. A. Bailey, K. C. S. Kwok, “Interference excitation of twin tall buildings”, Wind Engineering and Industrial Aerodynamics, Vol. 21, 323~338, 1985.
【5】Yuan-Lung Lo, Yong Chul Kim, Yi-Chao Li, “Downstream interference effect of high-rise buildings under turbulent boundary layer flow”, Wind Engineering and Industrial Aerodynamics, Vol. 159, pp. 19~35,2016.

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