加速氣流對於二維圓柱模型之氣動力行為探討

自工業時代以來，持續的燃燒化石燃，使大氣溫度不斷上升，然而天氣變得更加極端，這意味著會有更猛烈的風暴、強風。這些天氣變化也帶來了挑戰。而台灣地區位處於熱帶地區，每逢夏季受熱帶氣旋影響，每年平均會出現三次以上的颱風侵襲，然而天災帶來的損失是極其重大，因此在結構物安全性及舒適性的考慮是不可或缺的。然而世界各地對於風載重之設計皆有一定程度之發展，有著相當多理論以及規範，不過皆是基於較穩定之風場狀況來進行探討，忽略許多實際存在於大自然中急劇變化的天氣現象，使得在設計上趨於保守。颱風、雷雨等急劇變化的天氣特性對於建築物之影響，將會是未來著重探討的項目之一。本研究利用位於淡江大學風工程研究中心的主動控制型、開放式複數風扇風洞機具，探討當氣流在穩態流和急加速的變化下對於二維圓柱之氣動力現象;本研究主要分成四個部分進行實驗：(1)使用淡江複數風扇風洞模擬定常性流場風速範圍為4 m/s ~ 14 m/s以每1 m/s作為間隔，共有11種均勻風速剖面，與非定常性流場4 m/s加速至14 m/s，加速時間2s、4 m/s加速至14 m/s，加速時間5s兩種加速氣流場。(2)將圓柱模型放入上述(1)進行定常性以及非定常性之風洞試驗。完成上述(1)、(2)項實驗後，再進行(3)模型係數的探討，比較圓柱模型在不同的穩態流(低紊流)及加速氣流下的表面風壓分布特性及拖曳向、升力向風力係數的差異。(4)進而改變加速區間探討加速區間的變化是否會造成係數上的影響。數據分析上，透過比對算術平均（Arithmetic average）以及集合平均(Ensemble average)之概念，數據在定常性以及非定常性下的一致性以及正確性。針對渦散特性之探討則使用短時傅立葉轉換(STFT)。然而更進一步探討圓柱是否與深寬比1:1之方柱在非定常性流場下，模型表面風壓與風力係數是否有相同的現象發生，並討論加速區間的長短是否會因幾何形狀的關係而有不同的趨勢。

關鍵字

加速氣流；二維圓柱；非穩態；風壓實驗

並列摘要

Since the industrial age, the continuous burning of fossil fuels has continuously increased the atmospheric temperature, also make weather more extreme, this means having more intense major storms and strong winds.These changes in weather pose challenges. Taiwan is located in the tropics, and it is affected by tropical cyclones in summer. There will be an average of three typhoons per year. causing extremely heavy losses. Therefore, it is indispensable to consider the safety and comfort of the structure. This study Investigation the aerodynamic behavior of the two-dimensional circular cylinder model excited by accelerating wind flows generated by the actively-controllable multiple fan wind tunnel at Tamkang university. The experiment has four phases. The first phase is to make a comparison test under steady flows; the second phase is to collect enough ensemble size of testing results under the accelerating flow. By comparing the concepts of Arithmetic average and Ensemble average, the consistency and correctness of the data under constant and unsteady nature. For the discussion of vortex characteristics, short-time Fourier transform (STFT) is used. However, we further explore whether the cylinder and the square column with an aspect ratio of 1:1 are in an unsteady flow field, and whether the wind pressure on the model surface and the wind coefficient have the same phenomenon, and whether the length of the acceleration interval will be affected by the geometry Relationships have different trends.

並列關鍵字

Accelerating Flows ； Circular cylinder ； Non-stationary ； Pressure coefficient

參考文獻

【1】 ANSYS FLUENT Theory Guide. (2011). Release 14.0, Nov.

Google Scholar

【2】 Biggs. (1954). Wind Load on Truss Bridges. ASCE, 879.

Google Scholar

【3】 Cheng Xiao-Xiang Zhao Lin Ge Yao-Jun. (2016). Field measurements on flow past a circular cylinder in transcritical Reynolds number regime. Wuli Xuebao/Acta Phys. Sin. 65.

Google Scholar

【4】 Cobra Probe. (2015). Turbulent Flow Instrumentation Pty .

Google Scholar

【5】 Geric& EckelmaeD. (1982). Influence of end plates and free ends on the shedding frequency of circular cylinders. J. Fluid Mech.vol. 122, pp. 109-121.

Google Scholar

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加速氣流對於二維圓柱模型之氣動力行為探討

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