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標題: Experimental Study on Self-Sustained Oscillating Characteristics between Two Tandem Bluff Bodies
作者: 郭正雄
關鍵字: Tandem Bluff Bodies;縱列鈍體;太空科技;Self-Sustained Oscillation;Shear Layer Instability;Wavelet Analysis;PIV;自激式振盪;剪力層不穩定坡動;小波分析;PIV;應用研究
計畫名稱:縱列雙鈍體間流場特性之轉換與減阻機制的實驗探討本研究擬以二年之時程利用高質點密度之高速PIV系統,量測具有不同形狀、不同中心間距,以及不同之排列順序的縱列鈍體間以及下游鈍體尾流的全流域流場結構與特性。例如:相位平均或瞬間速度場、渦度、擾動能量之分布、環流量,以及剪力層在側展方向之變化,期望深入了解縱列鈍體間多樣化的流場特性形成之機制。各年之工作重點如下:第一年:首先,以LDA以及熱膜測速(HF)系統為主,同步量測流場中的速度信號,並以小波分析法探討當雷諾數為1000時,不同形狀(非圓柱)的縱列雙鈍體具有不同中心間距時,流場中的特徵頻率,以及縱列鈍體間剪力層波動的相位隨著時間之變化;瞭解是否與縱列雙圓柱同樣具有自激式振盪的特性。其二,撰寫相位平均分析技術之程式,並完成測試。利用高速高質點密度之PIV系統量測具有不同形狀(非圓柱)、不同中心間距的縱列鈍體間以及下游鈍體尾流場之特性;量化全流域流場之物理量,諸如:相位平均或瞬間之速度場、渦度、擾動能量等分布,以及下游鈍體尾流之環流量隨時間之變化等,期望進一步了解縱列鈍體間不穩定剪力層特性之變化與下游鈍體尾流交互作用之影響。第二年:同步量測流場中的速度信號,並以小波分析法探討在相同雷諾數時,不同形狀(非圓柱)、不同中心間距、不同排列順序的縱列雙鈍體具有不同中心間距時,流場中的特徵頻率,以及縱列鈍體間剪力層波動的相位隨著時間之變化。利用高質點密度之高速PIV系統量測不同形狀、不同排列順序的縱列鈍體間以及下游鈍體尾流的相位平均或暫態的全流域流場結構特性。量化全流域流場之物理量(與第一年同),深入了解不同形狀、不同排列順序的縱列鈍體間不穩定剪力層特性之變化與其下游尾流交互作用之影響。並與第一年之結果比較其異同與優劣。利用高質點密度之高速PIV系統量測分離剪力層在側展方向的流場結構,了解具有不中心間距時,縱列鈍體間剪力層在側展方向(z方向)的變化與雙鈍體間xy截面上流場特性之變化關係。以小波方法進一步分析側展(Spanwise)方向次渦漩(Secondary Vortices)流場結構之波數(Wave Number),進一步了解縱列鈍體間剪力層不穩定波動(Kelvin Helmholtz Instability)的三維性與縱列鈍體間多樣化流場特性形成之影響與所扮演之角色,以及與下游尾鈍體尾流場之交互作用。

Experimental Study on Self-Sustained Oscillating Characteristics between Two Tandem Bluff BodiesThis two-year project is proposed to investigate experimentally the mechanism for the self-sustained oscillating characteristics between two tandem bluff bodies at Reynolds number around 1000. It is to measure, via high speed high particle density PIV system, the phase-averaged or instantaneous velocity field between two tandem bluff bodies and the wake flows behind the downstream bluff body at various longitudinal spacing. Besides, the instantaneous spanwise flow structures of the separated shear layers will also be evaluated. It is intended to understand the influence of the secondary vortices on the flow characteristics between tandem bluff bodies with the hope to unveil the mechanism for the versatile flow characteristics between tandem bluff bodies. The contents are listed as follows.he first year: For the tandem bluff bodies of the same size but different shape, the flow characteristics between the bluff bodies of various longitudinal spacings are characterized via the LDA and hot film signals and the wavelet analysis. Using the PIV system, the instantaneous flow structures (in x-y plane) between tandem bluff bodies and the wake flow behind the downstream bluff body are measured. Develop the conditional sampling technique that can evaluate the phase-averaged flow field, the vorticity contours, the fluctuating energy distributions within the oscillating cycle, and the time-dependent circulation behind the downstream bluff body as the bases to relate the versatile flow structures between tandem bluff bodies and the interaction with the wake behind the downstream bluff body.he second year: At the same Reynolds number, determine whether the self-sustained oscillating feature exists between tandem bluff bodies of different shapes arranged at various sequences and spacings via LDA, hot film and the wavelet analysis. Using the PIV system, the phase-averaged characteristics of the corresponding flow structures are determined to understand the extent of the mutual interactions of the flows between tandem bluff bodies and the downstream wake. Further, the PIV system oriented in the spanwise direction in conjunction with the LDA signal is employed to investigate the degree of spanwise variation (or the secondary vortices) of the separated shear layerbetween two tandem bluff bodies. The wave number in the spanwise direction will be evaluated in order to unveil the role of the spanwise flow on the versatile flow patterns between tandem bluff bodies.
其他識別: NSC97-2221-E005-039-MY2
Appears in Collections:機械工程學系所

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