Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/13902
標題: 均勻來流中二維梯形鈍體紊流流場之數值探討
Numerical Investigations on Flow Around a Two-Dimensional Trapezoidal Bluff Body
作者: 陳鴻嵐
Chen, Hung Lan
關鍵字: Computational Wind Engineering;計算風工程;Large Eddy Simulation;大渦模擬
出版社: 土木工程學系
摘要: 
鈍體在風域中的受風效應之分析一向為建築研究領域裡重要的一環,為了獲取結構物承受之風荷重,以為推算其相應動態反應之依據,現行的方法多採用簡化狀況的風洞試驗配合實場量測資料而得之風函數。但此類風函數並不足以提供實際情況中複雜幾何與流力狀況下準確之風荷重數據,如結構物之造型特殊、風場中存在著其他建築物、或當來流屬非典型風況時,應用此類函數於設計中將導致誤差,甚至造成不保守的結果。
本研究旨在以微可壓縮流加大渦模擬的方法,計算均勻來流中二維梯形鈍體紊流流場。研究中以雷諾數為107,在均勻來流下流經梯形斷面,變化幾何形狀與風攻角探討流場特性之相關特性,期藉流場之模擬系統化地探討梯形結構物受到風力作用所引起的氣動行為。
研究結果指出,風攻角對於流場的速度場及風力係數的影響大於幾何斷面的影響。當流場雷諾數大於105後,流場已具備不變性。平均阻力係數 值隨著幾何張角之增大而增大,而平均昇力係數 亦是隨著來流攻角之遞增而遞增,在攻角為零時有最小之擾動阻力係數 與擾動昇力係數 值。而在低攻角下(-2O≦α≦+2O)昇力係數之頻譜受梯形截面上下方之渦散剝離頻率影響且出現單一主頻;一般而言當幾何角為15度時有較佳之風力效應,但當風攻角較大時會有較大之昇力攝動量需謹慎注意。

Investigation on flow around a bluff body has been an important subject in building research. To evaluate the dynamic response of a structure, the flow effects on the body and related flow characteristics are necessary during the design stage. Nowadays, there are mostly obtained by wind tunnel model testings. However, the accuracy of the experimental results usually suffers from scale effect. Besides, the achievement of the complete flow data is generally costly. Therefore, the application of high-speed computation in flow simulation becomes an important way of the analyses.
The objective of the study is to investigate numerically the turbulent flow around a two dimensional trapezoidal bluff body. In the study, a weakly-compressible-flow method incorporated with a space-average large-eddy-simulation technique is adopted. By varying the shape of the trapezoidal deck section and the attack angle of the approaching flow, the resulting surrounding flow characteristics and the wind effect on the body are assessed.
Results show that the major influence of the flow characteristics is the approaching-flow attack angle. As the geometric angle of the trapezoidal body increases, the mean drag coefficient also increases. On the other hand, as the attack angle increases, the mean lift coefficient also increases. When the angle of attack is zero the root-mean-square values of the drag and lift coefficient become minimum. When the attack angle is small, the spectrum of lift coefficient shows a single peak. Generally, a better wind effect on the body is obtained as the geometric angle equals 15o. However, it may result in a large fluctuating lift force at a large attack angle. Finally, The general characteristics of the flow remains unchanged as Reynolds number exceeds about 105.
URI: http://hdl.handle.net/11455/13902
Appears in Collections:土木工程學系所

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