臺灣博碩士論文加值系統

本論文主要探討縱列半圓柱間距內與下游流場的特性，雷諾數固定為1000。運用質點影像測速儀對流場結構進行瞬間速度場之量測，再透過適當正交分解方法分析，深入了解間距中與下游尾流場結構的變化，並將流場分類。結果顯示：下游尾流結構均為卡門渦列，其差異為渦漩形成強度的不同。但在間距中的流場結構可分為四種類型：當間距為S/D=0.1~0.9時，間距中的流場結構具有週期性的吸噴現象，特徵頻率與下游尾流者相同，且兩者皆高於單一圓柱，此時，下游尾流渦漩強度最強。當間距為S/D=1.0~3.5時，間距的前半部為平順剪力層，而後半部仍呈現週期性吸噴，但其振盪振幅較弱。此時，間距內之特徵頻率仍與下游者相同，但隨著間距變大其值逐漸下降，且下游尾流渦旋強度也持續減弱。當間距為S/D=4.0~4.5時，間距中的流場已不具有週期性的吸噴特性，但具有空穴自激式振盪特性。此時，在間距的上、下緣剪力層形成對稱的渦漩結構，其不穩定波動的史卓赫數約等於2。此時，其下游尾流強度持續減弱。當間距為S/D=5.0時，間距中的流場處於自激式振盪特性與兩個交替脫離尾流流場結構的轉換階段，其尾流強度為最弱，但在間距內與下游尾流的特徵頻率相同，也與下游單一半圓柱者相同。

The study investigates the flow characteristics in the gap between and downstream of two half cylinders arranged in tandem at the Reynolds number 1,000, based on the cylinder diameter. The particle image velocimetry is employed to measure the flow field and the proper orthogonal decomposition method is used to analyze the coherent flow structures. It is found that in the downstream region, the flow structures are the Karman vortex-street. The strength of circulation and the frequencies decreases mildly as the gap increases. However, in the gap region, four kinds of flow characteristics are categorized. As S/D=0.1~0.9, the flow in the gap exhibits periodic blowing/suction at the same frequency as that in the wake. This frequency is higher than that behind a single cylinder of the same diameter and the circulation strength is the strongest. For S/D=1.0~3.5, the fluctuating amplitudes are larger near the trailing-edge than that near the leading-edge of separating shear-layer across the gap. As the gap increases, this frequency in the gap decreases and the coherency of the periodic blowing/suction becomes less pronounced. The characteristic frequencies in the gap and in the wake are the same and also greater than that behind a single cylinder of the same diameter. For S/D=4.0~4.5, the vortex structures along the upper and the lower separating shear-layers are symmetric. For these gaps, the characteristic of self-sustained oscillations is found and no periodic blowing/suction is detected in the gap. The characteristic frequency in the gap is about 1.6 times that in the wake. For S/D=5.0, multiple characteristic frequencies are detected, representing that the flow structures in the gap switches between the self-sustained oscillations and the shedding vortex streets.

摘要 i
Abstract ii
目錄 iii
圖目錄 v
表目錄 x
符號表 xi
第一章 緒論 1
1-1 研究動機及目的 1
1-2 文獻回顧 2
1-2-1 渦流流量計之應用實例-單一鈍體 2
1-2-2 渦流流量計之應用實例-縱列鈍體 3
1-2-3 適當正交分解方法 6
第二章 實驗設備與數據分析方法 8
2-1低速循環水槽 8
2-2 三維精密移動平台 8
2-3 實驗架構和模型 8
2-4 質點影像測速儀系統介紹 9
2-5 具有特徵頻率的速度擾動量振幅分析 11
2-6 剪力層分析 11
2-7 開縫出口方向速度分析 12
2-8 環流量分析 13
2-9 適當正交分解法(Proper Orthogonal Decomposition)[2] 14
2-10 間距上方之水平方向力量計算 16
第三章 實驗結果與討論 18
3-1 單一圓柱與單一半圓柱之流場結構探討 18
3-2適當正交分解與相位平均法差異 18
3-3縱列半圓柱間與下游流場結構特性探討 19
3-3-1 不同間距對縱列半圓柱間流場影響 19
3-3-2 縱列半圓柱之頻率分析 21
3-3-3 縱列半圓柱間距中流場特性探討 21
3-3-4 縱列半圓柱尾流流場結構特性探討 23
第四章 結論 25
參考文獻 27

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