低雷諾數繞流振盪有限圓柱之鎖定效應

Lock-in phenomenon of low Reynolds number flow past a vibrational finite-span circular cylinder

陳逸儒(Yi-Ju Chen)

指導教授 ： 朱錦洲

共同指導教授 ： 張建成(Chien-Cheng Chang)

國立臺灣大學/工學院/應用力學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202102865

摘要

本篇文章在研究有限長圓柱在低雷諾數流場中進行簡諧振盪的數值模擬。
計算模擬的使用的軟體為一般商用軟體Ansys Fluent。
有限長圓柱在特定的條件下，BCP面(bisectional cross section plane)的SP(saddle point)與MCP面(middle cross section plane)的CS(center of source)上會有重和的現象，造成會有類點源的現象發生，在本篇文章中針對有限長振盪圓柱在雷諾數從Re=50-100，AR(aspect ratio number)的範圍從1.5到5尾流型態做分類，定義ss強度與狹長度做歸納統整與解釋，並利用高斯球面解釋類點源並非真正的源。
振盪圓柱在特定的範圍下會有鎖頻的效應，將使用快速傅立葉法分析主頻，調整圓柱強制振盪頻率fb與自然脫落頻率f0之間的比值與AR值、A/D值，在Re=90、AR=1.5-4、fb/ f0=0.8-1.2、振幅A(amplitude) / D=0.2、0.3，來做鎖定現象的討論。歸納出有限圓柱的鎖頻範圍因為AR值造成和文獻有所不同，並針對有限長圓柱在振盪過程中，會因為AR值與A/D的不同造成升力跳躍的現象。

關鍵字

有限長圓柱 ； 鎖定現象 ； 低雷諾數 ； 類點源 ； 振盪圓柱

並列摘要

This article is studying the numerical simulation of vibration finite-span circular cylinder in low Reynolds number flow.
The software used for calculation and simulation is general commercial software Ansys Fluent.
The finite-span circular cylinder under certain conditions, the SP (saddle point) of the BCP (bisectional cross section plane) and the CS (center of source) of the MCP (middle cross section plane) will overlap and rejoin together, resulting in a similar point source. In this article, we classify the wake pattern of a finite length oscillating cylinder with Reynolds number from Re=50-100 and AR (aspect ratio number) from 1.5 to 5, and define the source strength and slenderness will be summarized and explained. We also use Gaussian surface to explain that point source are not real source.
The oscillation cylinder will have a lock-in phenomenon in a specific range. Fast Fourier transform will be used to analyze the dominant frequency, and the ratio between forced oscillation frequency fb and the natural shedding frequency f0 of the cylinder will be adjusted in Re= 90, AR=1.5-4, fb/ f0=0.8-1.2, A(amplitude) / D=0.2, 0.3,discuss the lock-in phenomenon. It is concluded that the lock-in range of the finite cylinder is different from the literature due to the AR value, and for the finite-length cylinder in the oscillation process, the lift jumps due to the difference in the AR、A/D value.

並列關鍵字

finite-span circular cylinder ； lock-in phenomenon ； low Reynolds number ； source like pattern ； oscillating cylinder

參考文獻

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