流場流經有限高圓柱表面之三維流場現象為學者探究之目標，有限高圓柱雖然形狀簡單但其形成之流場三維結構卻極為複雜，由於分離泡存在使流場於不同雷諾數區間產生不同現象，若於光滑圓柱加上粗糙度則能使整體現象於較低雷諾數時發生。
本研究主要目標為以二進位排名法將光滑與粗糙圓柱表面之分離泡分佈進行統計。首先，判別壓力孔訊號是否有分離泡生成，將有分離泡之狀態設定為1，無分離泡則為0，再將所有壓力孔蒐集到之0與1訊號以二進位方式統合，將其數值進一步進行排名分析，藉此得知分離泡於臨界轉換區之流場分佈情況與出現機率，其結果可充分說明分離泡於臨界轉換區之間歇性、非對稱性，非同步性，同時，此方式能描述瞬時分離泡之分布結構，藉此觀察高寬比2-4之分離泡分佈變化。隨後於圓柱表面套上布料，測量圓柱於有粗糙度下之流場差異，與分離泡非定常現象，探討粗糙度對有限高圓柱流場，於臨界轉換區對分離泡之影響。

The three-dimensional structure of the flow field on a finite-height circular cylinder is extremely complex, while its simple shape. Under critical transition conditions, the generation of separation bubbles causes different phenomena in the flow field at different Reynolds numbers. Adding roughness to a smooth cylinder can induce these phenomena at lower Reynolds numbers, and the location of the separation bubbles can also be different.
The primary objective of this study is to statistically analyze the distribution of separation bubbles on the surfaces of smooth and rough finite-height circular cylinders by using a binary ranking method. Firstly, we determine whether the pressure signals have separation bubbles or not, and set the state of having separation bubbles as 1 and no separation bubbles as 0. Then we combine all the 0 and 1 signals in a binary way, and analyze the values in a ranked way. The results can illustrate the intermittent, asymmetric, and asynchronous nature of the separation bubble in the critical transition region on the circular cylinder with aspect ratio of 2-4. This method describes the distribution structure of the instantaneous separation bubbles, and we observe the changes in the distribution of the separation bubbles on the surface of a cylinder with an aspect ratio of 2-4.
After that, we put a fabric on the surface of the cylinder and measure the flow field difference and the non-stationary phenomenon of the separation bubbles under the roughness of the cylinder to investigate the effect of roughness on the flow field of a finite height cylinder on the generation of separation bubbles under the critical transition condition.

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