本研究針對脈衝雙環噴流，藉由實驗方法研究噴流的流場行為與混合特性。透過電磁閥使環噴流產生脈衝特性，利用雷射光頁輔助流場可視化技術，觀察瞬時煙霧流動影像、脈衝流動衍化過程及長時間曝光流場照片；針對長時間曝光照片，利用二階邊緣偵測影像處理技術，計算噴流擴散寬度；使用熱線風速儀量測軸向與徑向速度分佈；透過拓撲流動形態解釋渦漩流動結構；利用質點影像速度儀檢視時間平均速度場；使用追縱氣體濃度偵測技術研究噴流擴散特性。在中心噴流雷諾數與環流雷諾數的域面上，可畫分出三個流場特徵模態，分別為環流主導模態、中心噴流主導模態-低剪切及中心噴流主導模態-高剪切。當脈衝環流在高振幅時，環流的軸向動量明顯地轉換為徑向動量，導致環流內部與外部剪流層形成，並且往橫向造成分歧。環流的內部剪流層渦漩往中心噴流偏折並衝擊中心噴流，在環流主導模態時，間歇地形成停滯點於中心軸附近；環流的外部剪流層渦漩往下游滾動，使流場形成大的噴流擴散。因為環流脈衝的強列衝擊，使得廻流區沿軸向增長，造成流場大的紊流擾動。在中心噴流主導模態-低剪切時，中心噴流足夠強健，將廻流區對分，中心噴流強列牽引控制噴流在橫向的擴散。在中心噴流主導模態-高剪切時，迴流區往中心線收縮，並且與中心噴流結合。流場的紊流強度在心噴流主導模態-低剪切及中心噴流主導模態-高剪切較不顯著。脈衝雙環噴流混合特性的增強主要受兩種局部流場結構影響；中心軸附近間歇形成的停滯點以及流場中的大紊流擾動。因此，環流主導模態的混合性能被顯著地增強。計算徑向擴散改善指數的結果顯示，雙環噴流之環流受到大振幅脈衝時，混合能力可提升約80%。

The flow behaviors and mixing characteristics of the pulsed double-concentric jets were investigated experimentally. The annular flow pulsation was generated by employing a solenoid valve. The instantaneous smoke flow patterns, evolution process of the pulsed flow, and long-exposure flow patterns were observed by means of the laser-light sheet assisted flow visualization method. A binary edge-detection technique was used to compute the jet spread width by using long-exposure flow images. Velocity distributions on the axial and radial directions were measured by a hot-wire anemometer. Topological flow patterns were analyzed to interpret the vortical flow structures. The time-averaged velocity fields were examined by utilizing the Particle Image Velocimetry. The tracer gas concentration detection technique was used to study the dispersion characteristics. Based on the flow patterns and topological structures, four characteristic flow modes were identified in the domain of the central jet and the annular flow Reynolds numbers, namely the annular flow dominated mode, transition mode, central jet dominated mode-low shear, and central jet dominated mode-high shear. When the annular flow was pulsed with high amplitudes by the solenoid valve, the transition mode disappeared. The radial momentum of the annular flow was increased and influenced the central jet drastically in the annular flow dominated mode. Stagnation points were intermittently witnessed on the central axis. The annular flow was expanded both axially and radially. The axial expansion elongated the vortices of the recirculation region downstream the flow direction and vanished a pair of vortices that were formed in the annular flow dominated mode of the double-concentric jets. The radial expansion assisted to achieve large jet spread width. However, the jet spread width was reduced at the high annular Reynolds numbers with a strong saddle on the central line. These elongations created large fluctuations by deflecting the central jet to disperse in the recirculation region. The influence of the annular flow was reduced in the central jet dominated mode. The central jet entrainment increased with increasing the central jet Reynolds number. The turbulence fluctuations were insignificant in the recirculation region in the central jet dominated mode. The mixing properties of the double-concentric jets were enhanced by two major phenomena: the formation of the stagnation points on the central line and the large turbulence fluctuations in the near flow field. Therefore, the mixing behaviors were prominently enhanced in the annular flow dominated mode. The radial dispersion improvement index revealed that the mixing capability between the jets could be enhanced up to 80% in the recirculation region by applying high amplitude pulsations on the annular flow.

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