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研究生： Navik Kholili
Navik Kholili
論文名稱： 噴流到平板的距離對壁面噴流之流場特徵的影響
Effects of jet-to-wall distance on flow characteristics of wall jets
指導教授： 黃榮芳
Rong-Fung Huang
口試委員: 許清閔
Ching-Min Hsu
LE MINH DUC
LE MINH DUC
黃榮芳
Rong-Fung Huang
學位類別： 碩士
Master
系所名稱： 工程學院 - 機械工程系
Department of Mechanical Engineering
論文出版年： 2018
畢業學年度： 106
語文別： 英文
論文頁數： 167
中文關鍵詞： wall jet 、offset jet 、jet to plate distance
外文關鍵詞： wall jet, offset jet, jet to plate distance
相關次數： 點閱：194  下載：1 
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  •  上一筆

    • 針對一連續噴流平行流過一平板時，利用實驗方法研究平板上的流場特徵與速度特性。實驗參數為噴流雷諾數，噴流至平板的軸向距離及噴流至平板的徑向距離。藉由流場可視化的技術，觀察平板上方的瞬時煙霧流場照片。使用熱線風速儀量測平板上方的速度分佈和紊流性質。應用質點影像速度儀量測平均速度向量場與流線圖，渦度輪廓和速度特性。實驗結果發現，在噴流雷諾數與徑向的噴流至平板距離之域面上，可畫分出兩種特徵流動模式：貼附噴射及分離噴流。流場特徵主要受到噴流至平板的徑向距離支配。在小徑向的噴流至平板距離時，噴流氣柱(其包括從射流柱發展而來的渦旋結構)貼附在平板上，而在大徑向的噴流至平板距離時，噴流與平板分離，無任何接觸。噴流至平板的軸向距離對流場特徵影響則不明顯。由於噴流氣柱貼附在平板上，渦旋結構沿著軸向移動產生變形，形狀失去凝續性，接續著破碎成紊亂的小渦漩。因此，噴流的明顯地往橫向擴散。中心線上的速度分佈，速度沿著軸向距離增加而衰減。中心線擾動強度出現兩個峰值。漩渦結構的第一個形成的位置大約在第一個峰值處。渦旋結構破碎成紊亂小渦漩的位置大約在第二個峰值處。分離噴射模態之流場和速度特性，則與自由噴流相似。

    The flow and velocity characteristics of a continuous jet flowing tangentially over a flat plate were experimentally investigated. The jet Reynolds number, axial jet-to-plate distance, and radial jet-to-plate distance were varied. Flow visualization technique were performed to obtain the instantaneous smoke flow patterns. The velocity distributions and turbulent properties were detected using a hot-wire anemometer. The Particle Image Velocimetry (PIV) technique was used to reveal the average velocity vectors and streamlines, vorticity contours, and velocity characteristics. Two characteristic flow modes were identified in the domain of jet Reynolds number and radial jet-to-flat distance: attached jet and detached jet. The flow characteristics are primarily dominated by the radial jet-to-plate distance influences. The jet column (which includes the vortical structure evolved from the jet column) attaches to the flat plate at small radial jet-to-plate distance, whereas that detaches from the flat plate at large radial jet-to-plate distance. The effect of the axial jet-to-plate distance on flow characteristic is insignificant. As the jet column attaches to flat plate, the vortical structures deform, become less coherent, and continue to break up into turbulent eddies. Therefore, the jet spreads toward lateral direction significantly. The centerline velocity decays with the increasing axial jet-to-plate distance. The centerline fluctuation intensity appears two peaks. The first formation of the vortical structure locates at around the first peak. The breakup position of vortical structure locates at around the second peak. For the detached jet mode, the flow and velocity characteristics exhibit similar to those in the case of a free jet.

    ABSTRACT i 摘要 ii ACKNOWLEDGEMENTS iii TABLE OF CONTENTS iv NOMENCLATURE vi TABLE CAPTIONS vii FIGURE CAPTIONS vii CHAPTER 1 1 Introduction 1 1.1 Motivation 1 1.2 Literature Survey 1 1.3 Scope of present work 3 CHAPTER 2 5 Experimental Methods 5 2.1. Experimental set up 5 2.1.1 Continuous jet 5 2.1.2 Smoke generator 5 2.2. Experimental method 8 2.2.1 Flow visualization 8 2.2.2 Hot-wire anemometer velocity measurement 9 2.2.3 PIV measurement 9 CHAPTER 3 12 Flow Characteristics 12 3.1 Free jet 12 3.2 Wall jets 13 3.2.1 Flow patterns in the horizontal plane 13 3.2.2 Flow patterns in the vertical plane 15 3.3 Characteristic flow mode 18 3.4 Vortices formation length 19 CHAPTER 4 21 Vortices and Turbulence Properties 21 4.1 Velocity and turbulent intensity distribution along central axis 21 4.2 Velocity and turbulent intensity distribution along radial axis 23 CHAPTER 5 26 Velocity Fields 26 5.1 Time-averaged velocity vectors and streamlines 26 5.1.1 Free jet 26 5.1.2 Wall jets 27 5.2 Time average vorticity contours 31 5.2.1 Free jet 31 5.2.2 Wall jet 31 5.3 Time average velocity characteristics 34 5.3.1 Axial distribution of velocity characteristic 34 5.3.2 Radial distribution of velocity characteristic 37 CHAPTER 6 40 Conclusion and Recommendations 40 6.1 Conclusion 40 6.2 Recommendation 42 References 43

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