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標題: 多圓柱流場之數值分析
Numerical Analysis of Flow Over Circular Cylinders in Various Arrangements
作者: 施洪寬
關鍵字: 多圓柱流場;高雷諾數
出版社: 機械工程研究所
本研究及探討在高雷諾數下,亦即為近非黏性流場,均勻流(Uniform Flow)流經一個或多個不同排列方式之圓柱所造成的流場。在滿足卡達條件(Kutta Condition)下,模擬自圓柱上固定脫落點脫落之大型漩渦結構及尾流現象,並得到整個圓柱流場之總體性質,如升阻力係數、史戳荷數(Strouhal Number)、壓力係數等。本研究利用表面過度法(Surface Vorticity Method)先求得流場之勢流解,再將此勢流解延伸,以離散渦流模式(Discrete Vortex Model)來模擬整個流場之現象。此外,並嘗試分析多圓柱流場之尾流干擾效應。
藉由與過去其他研究所得結果相比較,基本上對於一個圓柱之模擬,本研究已有不錯的結果,雖然CD與CL值比實驗值稍低,但對於St值,流場脫落型態,及整個流場總體性質變化趨勢之預測,比較下均有相當吻合的結果。此外,對於兩個及三個圓柱的情形,除了雙圓柱水平併放(Tandem)以外,本文所採用的方法均能有效的予以分析。而對於三個圓柱的情形,過去較少有資料可供比對,但由流場型態(Flow Pattern)趨勢來看,與視流實驗(Flow Visualization)所得之結果相比較下,亦有相當合理的結果。

The main purpose of this thesis is to analyze the flow field with the uniform flow over circular cylinders in various arrangements. The flow field is considered to be inviscid for high Reynolds number flows. By the satisfaction of the Kutta condition, the vortex shedding phenomena with fixed separation points behind the cylinders are carefully investigated. The global properties of the flow field are obtained from the numerical analysis. For solving the question, first, the surface vorticity method is applied to predict the solutions of the potential flow. Then the vortex shedding phenomenon at the separation points is simulated by the discrete vortex model. For more of analysis, we also try to analyze the interference effects of the wake flow for more than one cylinder case.
The predictions about the trend of the flow field in one circular cylinder are in good agreements with the other researches, but the values of CD and CL, as presented in this thesis, are lower than that from the experiments. For the cases of the two or three cylinders, the numerical scheme used in this dissertation predicts a reasonable results by comparing with the results from the flow visualizations and experiments except for the tandem arrangement of the two circular cylinders.
For the wake intrference study, it was found that the lift and drag forces of the downstream cylinder increase due to the effects of the upstream cylinder. As to the shedding frequency, flow effect to the Strouhal number is not obvious. It was found that the exist of upstream cylinder does not affect this quantity into large extent for the downstream cylinders.
Appears in Collections:機械工程學系所

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