為了探討光滑圓柱流場情況下臨界轉換區中分離泡形成之特性，本研究提出滑窗法(sliding window method)及峰谷法(peak-valley method)以辨識從圓柱模型兩側得到的壓力時間訊號中之間歇性跳動，於本研究中此間歇性跳動稱為特徵事件。由滑窗法和峰谷法得到的合格事件數量可知，峰谷法較容許壓力時間訊號中的小尺度干擾，因此較適合用於後續分析中。峰谷法從壓力時間訊號中辨識出特徵事件後，分為兩類：類型一事件為壓力下降事件，而類型二為壓力上升事件。隨後，計算出的每分鐘事件數量可用以描述分離泡形成的間歇性，且每個特徵事件的時間尺度代表分離泡形成之時間尺度。由結果可知，每分鐘事件數量在臨界轉換區內隨著雷諾數變化，且在預臨界至單分離泡轉換區中最高。雖然特徵事件的時間尺度會隨著雷諾數變化，在本研究三個案例中，預臨界至單分離泡轉換區中的無因次化時間尺度 L⁄(V_ref τ_F ) 之加權平均值接近文獻中升力跳動的時間尺度無因次化值。因此於物理層面而言，壓力時間訊號中的特徵事件與分離泡形成的三維特性有關。透過與特徵事件對應的短時交互相關分析，儘管三個案例中情況各有不同，但雙側事件之相關係數結果大多分布在1或-1左右，代表大多為同相或反相情況。然而因為高同步雙側事件數量不足，特徵事件無法進一步透過相關係數分類。
在本研究中也嘗試將峰谷法應用於T-40模型實驗，並且得到三種案例中可代表間歇性分離泡形成之特徵事件的無因次化時間尺度。由結果可知，無因次化時間尺度的機率分布圖較圓柱實驗結果少差異性，雖然三種案例中壓力係數隨雷諾數之變化有明顯不同。另外，T-40模型三種案例中的無因次化時間尺度皆在0.1到0.6之間，與圓柱實驗結果類似。需要更多不同模型的實驗結果以驗證本研究的發現。

To investigate the characteristics of the separation-bubble formation of flow over a smooth circular cylinder in the critical transition range, a sliding-window (SW) method and a peak-valley (PV) method were proposed to identify the intermittent jumps, named the characteristic events, in the real-time pressure signal obtained on both sides of the cylinder model. By evaluating the counts of the qualified events of the SW and PV methods, the PV method was found less sensitive to the small-scale disturbances in the real-time pressure signal, therefore was adopted for later analysis. With the PV method, the characteristic events were identified from the real-time pressure signal and categorized into two types: Type-1 is referred to the events of pressure descending and Type-2 is referred to the events of pressure ascending. Subsequently, the count per minute of the characteristic events was determined for describing the intermittency of the separation-bubble formation, and the time scale of each of the characteristic event was regarded as the time length of the separation-bubble formation. The count per minute of the characteristic events was varying with the Reynolds number in the critical transition range. As noted, it appeared to be the highest in the transition from pre-critical to one-bubble regime. Despite the time scales of the characteristic events were varying with respect to the Reynolds number, the weighting-averaged altered normalized time scales L⁄(V_ref τ_F ) in the transition from the pre-critical to one-bubble regime of the three cases studied were found comparable to the normalized time scale of the lift jump noted in the literature. Physically, the characteristic events found in the real-time pressure signals in this study can be attributed to the three-dimensional aspect of separation-bubble formation. By the short-time cross correlation corresponding to the characteristic event, the correlation coefficients of the two-side events in the three cases mostly distributed around 1 or -1, which represents in-phase or anti-phase situations, despite the results were various in the three cases. However, the characteristic events are not able to be further categorized by the cross correlation due to the lack of the highly overlapped two-side events.
The PV method was also applied on the experimental result of the T-40 model, the normalized time scales of the characteristic events that indicating the intermittent separation-bubble formation were determined in the three cases. The results showed that the histograms of the normalized time scales were relatively similar compared to those shown in the circular cylinder cases, although the variations of the pressure coefficients versus the Reynolds number are different in the three cases. Moreover, the altered normalized time scales in the three cases with T-40 model, which ranged between 0.1 and 0.6, are comparable to the results deduced in the circular cylinder cases. More experimental data with different model are required to verify the finding in this study.

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