臺灣博碩士論文加值系統

本研究針對直立圓管噴流受振盪橫風衝擊時，在風洞中使用實驗方法觀察橫風中之噴流的流場特徵行為及混合性能。在風洞下游處裝置一旋轉擋板，當擋板旋轉時，使得風洞測試段中的橫風產生週期性的速度振盪。藉由改變擋板的轉速及阻塞比，可改變橫風振盪的速度特性。本研究固定橫風速度振盪的頻率為4 Hz，橫風速度振盪的振幅為1 m/s，橫風雷諾數變化介於700與1,500之間，噴流對應橫風之動量通量比變化介於1.6至4.0之間，噴流在穩定橫風中的流場特徵為噴流型式流動。使用流場可視化技術擷取噴流於橫風中之瞬時與長時間曝光的流場影像；藉由影像邊界辨識技術取得噴流之穿透高度及擴散寬度。利用追蹤氣體濃度測試法，量測噴流於橫風中的混合特性。透過觀察瞬時流場的衍化照片，在橫風雷諾數及噴流對應橫風之動量通量比的域面上，可劃分出三種流場特徵模態，分別為波狀流動、擺動噴流及噴流主導模態。振盪橫風對噴流產生週期性地衝擊，在低噴流對應橫風之動量通量比時，噴流動量太低不足以抵抗振盪橫風的週期性衝擊，所以，噴流氣柱上下擺動，形成波狀流動行為。在高噴流對應橫風之動量通量比時，噴流動能足夠大，能夠承受振盪橫風的週期性衝擊，噴流在振盪橫風呈現噴流型式流動。在居中的噴流對應橫風之動量通量比時，振盪噴流的衝擊對噴流出口的氣柱造成前後擺動。在波狀流動及擺動噴流模態時，橫風噴流迎風面之剪流層渦漩會間歇性地消失。相較於噴流在穩態橫風中，噴流在振盪橫風中之穿透、擴散與混合較大。針對直立噴流於振盪橫風中的模態，波狀流動模態的穿透、擴散與混合的性能最佳。

Flow and mixing characteristics of a stack-issued jet in pulsating crossflow were experimentally investigated in an open-loop wind tunnel. A rotating baffle installed in downstream of wind tunnel was used to generate the periodic pulsating crossflow in test section. The pulsating conditions of the pulsating crossflow were controlled by the rotating speed and blockage ratio of the rotating baffle. The pulsating frequency and amplitude of the pulsating crossflow were fixed at 4 Hz and 1 m/s, respectively. The crossflow Reynolds number and jet-to-crossflow momentum flux ratio were within the ranges of 700 – 1500 and 1.6 – 4.0, respectively. The flow characteristic of the jet in steady crossflow is jet type flow mode. The characteristic flow patterns in the median and horizontal planes of the stack-issued jet in pulsating crossflow were captured by smoke flow visualization method. The penetration height and spread width of the transverse jet were measured by edge detection technique. The mixing properties of the transverse jet were detected by tracer-gas concentration detection method. According to the instantaneous flow patterns in median plane, three characteristics flow regimes—wavy flow, flapping jet flow, and jet dominated flow modes—were classified in the domain of crossflow Reynolds number and jet-to-crossflow momentum flux ratio. The pulsating crossflow produces periodic impingement on the stack-issued jet. At low jet-to-crossflow momentum flux ratio, the jet momentum is too low to sustain the periodic impingement from the pulsating crossflow. Therefore, the jet column tilts up-and-down and induces the wave flow behavior. At high jet-to-crossflow momentum flux ratio, the jet momentum is large enough to sustain the pulsating impingement of the crossflow. The jet in pulsating crossflow behaves jet type flow. At mediate jet-to-crossflow momentum flux ratio, the periodic impingement of pulsating crossflow induces back-and-forth flapping of the jet column near jet exit. The upwind side shear-layer vortices of the transverse jet disappear intermittently in wavy flow and flapping jet flow modes. The penetration, spread, and mixing of the jet in the pulsating crossflow are larger than those in steady crossflow. For the stack-issued jet in pulsating crossflow, the best penetration, spread, and mixing of the transverse jet is obtained in wavy flow mode.

摘要..........................i
Abstract.....................ii
誌謝.........................iv
目錄..........................v
表目錄.....................viii
圖目錄.......................ix
符號索引..................xxvii
第一章 緒論...................1
1.1 研究動機..................1
1.2 文獻回顧..................1
1.3 研究目標..................3
第二章 實驗設備、儀器與方法.....4
2.1 實驗設備..................4
2.1.1 風洞....................4
2.1.2 橫風擾動特性.............4
2.2實驗儀器....................5
2.2.1 風洞速度量測.............5
2.2.2 煙霧流場可視化...........6
2.2.3 濃度均勻度量測...........8
2.3 實驗方法..................9
2.3.1邊緣偵測方法..............9
第三章 流場特徵................11
3.1垂直中立面之流場特徵行為.....11
3.2 流場特徵模態...............13
3.3 水平切面之流場特徵行為......14
3.4 長時間曝光流場.............16
3.5 噴流擴散尺寸...............17
第四章 混合特性................21
4.1 追蹤氣體分佈...............21
4.2 混合寬度..................22
4.3 噴流軌跡...................23
第五章 結論及建議...............25
5.1 結論.......................25
5.2 建議.......................25
參考文獻.......................156
Extended Abstract.............158

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