本文使用實驗方法探討圓管噴流受橫流衝擊時，所形成之凝序性流體結構之特徵模式與衍化機制以及整體流場之特性。噴流係由一個特殊設計之空氣供應系統提供，橫流則由一低速風洞模擬產生。藉由雷射光頁輔助之煙霧流場觀察技術及高速質點影像速度儀(Time-resolved Particle Image Velocimeter, PIV)所獲得之垂直與平行切面的影像與速度資料，得以進行平均流場與瞬時流場之定性與定量分析。實驗過程同時利用熱線風速儀與高速資料擷取系統，針對噴流剪流層衍化生成之凝序性結構進行速度與特徵頻率診測。噴流對應橫流之動量通量比與橫流雷諾數為實驗的主要控制參數。分析圓管噴流出口附近剪流層之連續衍化照片與速度向量，在不同的噴流對應橫流之動量通量比範圍，確認出五種特徵型式渦漩，分別是「混合層式渦漩」、「向後滾轉渦漩」、「向前滾轉渦漩」、「搖擺引致蕈狀渦漩」與「噴流型式渦漩」。當動量通量比在0.49以下時，噴流動量較小且支撐性較低，噴流受衝擊後偏折角度較大。此時剪流層渦漩結構主要由剪切作用引致產生，此範圍之渦漩型式包含有「混合層式渦漩」、「向後滾轉渦漩」與「向前滾轉渦漩」。當動量通量比在0.49至1.01時，噴流與橫向流之動量差異減小且偏折現象減緩，横向流衝擊氣柱之影響逐漸超越剪切作用並引致管口附近氣柱產生前後搖擺運動。此時噴流渦漩結構主要由搖擺引致作用產生，此範圍之渦漩型式屬於「搖擺引致蕈狀渦漩」。當動量通量比大於1.01時，噴流動能超越橫流動能，此時氣柱搖擺運動停止，且剪切作用再度主導形成「噴流型式渦漩」結構。應用拓樸理論分析流場渦流運動，可明確分辨出節點、鞍點、焦點及分歧線等流線型態與分佈區域。藉由熱線風速計量得剪流層之即時風速資料，經過運算分析後可得特徵頻率、史卓荷數、功譜密度函數等數據，並發現史卓荷數隨噴流對應橫流之動量通量比增加，對應形成指數衰退型相關函數。應用樣本平均法，分別獲得垂直平面與水平面之平均流場特性，其中包含速度分佈、流線分佈與渦度分佈。本文另針對流場紊流特性，利用統計分析方法將速度資料分別轉換為紊流強度、紊流應力與紊流動能進行分析。

Characteristics and evolution mechanisms of the traveling coherent structure in the shear layer of an elevated jet in a crossflow are experimentally studied. The jet flow is supplied by a specially designed air supply system. A steel tube connected with the nozzle assembly is inserted into a crossflow formed by a low speed wind tunnel. The instantaneous and time-averaged flow field characteristics of the vertical plane as well as horizontal plane which are observed and measured by using a laser light-sheet flow visualization technique and a high-speed timed-resolved Particle Image Velocimeter (PIV) are qualitatively and quantitatively studied. Time histories of the instantaneous velocity of the vortical flows in the shear-layer are recorded by a hot-wire anemometer and a high-speed data acquisition system in order to analyze the frequency characteristics of the traveling coherent structure in the shear-layer. Experiments are performed at different jet-to-crossflow momentum flux ratios, and different crossflow Reynolds numbers. The behaviors and mechanisms of the vortical flow structure and the vorticity evolution mechanisms appear to be distinct in different flow regimes. By analyzing the streak pictures of the smoke flow visualization and the sequential vector maps, five kinds of vortices evolution mechanisms, “mixing-layer type vortices”, “backward-rolling vortices”, “forward-rolling vortices”, “swing-induced mushroom vortices”, and “jet-type vortices”, can be identified in the shear-layer evolving from the jet exit. When the jet-to-crossflow momentum flux ratios are lower than 0.49, the jet column is weak and bent severely so that the coherent structures of the shear layer are mainly induced by the shear force developed between the high-speed crossflow and the low-speed jet. There are three kinds of vortices “mixing-layer type vortices”, “backward-rolling vortices”, and “forward-rolling vortices” in the regime. When the jet-to-crossflow momentum flux ratios are increased in the range between 0.49 and 1.01, the jet column is getting strong and the bent angle is decreased which causes the decreased shear effect and increased impinging effect of the crossflow on the jet to induce a swing motion of the jet column near the tube-tip so that the “swing-induced mushroom vortices” are induced by the swing motion. When the jet-to-crossflow momentum flux ratios are larger than 1.01, the momentum of the jet is larger than crossflow and the jet column is strong enough to sustain the impingement of the crossflow so that the swing motion of the jet column is disappear and the shear force appearing in the upper shear-layer induces the “jet-type vortices”. The nodes, saddles, foci, and bifurcation lines of the flow structures can be identified by applying the topology method. The frequency characteristics, Strouhal number and power-spectral density functions are obtained by processing the measured instantaneous velocity data. The Strouhal number is found to decay exponentially with the increase of the jet-to-crossflow momentum flux ratio. The average characteristics of the velocity, streamline and vorticity distributions in the vertical and horizontal planes are obtained by applying the ensemble average method. The velocity data can be transferred to turbulent intensity, turbulent stress and turbulent kinetic energy by statistics method.

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