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Numerical Investigations on Flow Around a Two-Dimensional Trapezoidal Bluff Body
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:||
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.
|Appears in Collections:||土木工程學系所|
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