陳炳煇臺灣大學:機械工程學研究所李亦堅Lee, I-ChienI-ChienLee2010-06-302018-06-282010-06-302018-06-282007U0001-2312200708490000http://ntur.lib.ntu.edu.tw//handle/246246/187017主流場內噴流 (Jets in a cross-stream) 為描述氣柱噴入一非平行之均勻主流場，由於機制具有許多重要應用而被廣泛研究，其中薄膜冷卻為主要應用之一，此為利用冷噴流產生貼近壁面之氣膜以保護下游壁面不受高溫主流場燒毀。在本研究中，實驗探討空氣流從一具有端點前擴張角並沿主流場流動方向之前傾斜孔進入凹型曲面上均勻主流場之混合流場結構，其中噴流結構涵蓋單一噴射孔及單排5橫向排列噴射孔。實驗中利用質點影像測速儀(PIV)瞬間量測二維截面速度場，以獲得詳細之平均速度流場結構，以及使用數位CCD感測器，擷取欲觀測流場之二維截面上雷射光頁所產生煙霧結構，以獲得可視化瞬間、平均之流場結構。單一空氣柱進入橫向主流場，主要探討在4種不同噴流/主流場速度比下（M=0.5 、1.0、1.5 及 2.0），噴流流場之可視化結構及平均濃度分佈，進而量測M=1.0下二維截面速度場，以獲得平均速度場及紊流強度。量測結果顯示，噴流/主流場速度比對單一空氣柱進入橫向主流場具有重要影響。由孔中心面二維平均速度場顯示，在M=1.0下，噴流與主流場之較劇烈混合發生在噴流背風側，橫向主流進入此區產生向上速度分量推使噴流遠離壁面，此橫向主流產生向上速度分量隨向下游位置移動而減小，最終造成噴流貼近凹型曲面流動。單排5孔空氣柱進入橫向主流場，主要探討在M=1.0下，流場之可視化結構、平均濃度分佈，與二維截面平均速度場、擾流強度、以及三維流場。量測結果顯示，由於近噴射孔下游端處具有向上平均速度分量顯示噴流於此區處具有向上推升力。噴流於噴射孔出口產生ㄧ對流線方向反轉渦漩流(Counter-rotating Vortex Pair)，並由其流動模態可將噴流依不同橫向位置，依序歸納成上升直線流（a straight flow zone）、渦漩流（a swirling flow）、及下洗流（touch-down flow）。此外，橫向主流場流經一單排噴射孔時受噴流流場影響甚劇，位於近壁面之邊界層（Z/D = 0.13）內之橫向主流受噴流主流場方向速度影響而加速，且部分受噴流導引進入噴射孔下游處，並當高度Z/D=0.88時橫向主流可穿越噴流。本實驗中，噴流為經由一具有出口端前擴張角之前傾斜孔噴出，其具有較大主流場方向速度分量及較貼近壁面之特性，此將削減馬靴型渦漩（Horseshoe vortex）之產生。This study investigates two flow fields injected into a cross-stream over a concave surface: 1) an inclined jet ejected from a forward expanded hole, and 2) five inclined jets ejected from a row of forward expanded holes. The complex flow fields between the jets and the cross-stream were measured using both digital particle image velocimetry and a flow visualization technique. This study contributes to measurements of the 3D time-averaged velocity field and to classify which flow is dominant. In a viewpoint of film cooling, the domination of jet flow or cross-stream in the flowfield will affect the cooling efficiency.or a jet ejected in a cross-stream, this study presents the flow visualization and seeded particle time-averaged concentration at four different jet-to-cross-stream velocity ratios (M) of 0.5, 1.0, 1.5, and 2.0. Measured results show that the blowing ratio has a strong effect on the flow field of a single jet flow into a cross-stream. Results from the 2D velocity measurement on the central plane of the injection hole at M =1.0 show that a strong interaction occurs between the ejected jet flow and the cross-stream at the leeward side of the ejected jet. In this region, the cross-stream is entrained into the center plane, producing an outward radial velocity to lift the ejected jet flow away from the concave wall. The lift-off velocity decay from the cross-stream along the streamwise direction causes the jet flow to reattach to the concave surface.or the five jets ejected into a cross-stream, this study presents the flow visualization, detailed time-averaged velocity fields, velocity fluctuations, and flow patterns of both the jet flow and the cross-stream at a blowing ratio of 1.0. At the center plane of the injection hole, a strong positive vertical time-averaged velocity located on the downstream provides evidence for jet flow lift-off. A counter-rotating secondary-flow vortex pair immediately forms in the jet directly above the injection hole downstream. Depending on flow characteristics, the ejected jet flow at transverse locations can be categorized into three flow zones, namely, a straight flow zone, a swirling flow zone, and a touch-down flow zone. In addition, the jet flow greatly influences the cross-stream when it passes through a row of inclined jets over a concave surface. The brief trait of the cross-stream shows that the jet flow accelerates the cross-stream at the near wall region of Z/D=0.13 in the streamwise direction when the cross-stream passes through the region between adjacent jets. The jet flow at the near wall region of Z/D=0.13 induces the cross-stream to move towards the centerline of the injection hole. Above an elevation of Z/D=0.88, the cross-stream has enough streamwise momentum flux to pass through the main jet. For a cross-stream passed through a row of inclined jets with a forward expanded hole, the streamwise velocity increased by the jet flow and the close-to-wall jet will inhibit the horseshoe vortex. Streamwise jet flow vortices induce a cross-stream occurring behind the injection hole close to the wall surface.Abstract iist of Figures viiomenclature xivhapter 1 Introduction 1-1 Motivation 1-2 Literature review 2.3 Objectives 10hapter 2 Experimental Facilities and Techniques 12-1 Experimental apparatus 12-2 Geometry of ejected holes and the coordinate systems 13-3 Measurement techniques 14-3-1 Particle Image Velocimetry, PIV 14-3-2 Hot-wire anemometer and pressure transducer 15-4 Operating conditions 15-4-1 PIV conditions 15-4-2 Cross-stream conditions 17-5 Reconstruction of the three-dimensional time-averaged velocity field 17-6 Calibration and measured errors 20-6-1 Calibration of Particle Image Velocimetry 20-6-2 The seeding particles and the drifting of the particles 20-6-3 The hot-wire anemometer, the Static-Pressure transducer and the lowmeter 23-7 Accuracy of Particle Image Velocimetry data 25-8 Experimental uncertainty 27hapter 3 Cross-stream in the curved section 29hapter 4 Flow Visualization of a jet in a cross-stream 32-1 The instantaneous seeded particle images 32-2 Time-averaged seeded particle concentrations 35hapter 5 Two dimensional flow fields of a jet in a cross-stream 41-1 Two dimensional time-averaged velocity field on the center plane 42-2 Turbulent Intensity on the center plane 45hapter 6 Flow Visualization of a row of jets in a cross-stream 47-1 The instantaneous seeded particle images 48-2 Time-averaged seeded particle images and concentrations 49hapter 7 The time-averaged flow field of a row of jets in a cross-stream 53-1 The time-averaged velocity fields of the jet in a cross-stream 53-2 The time-averaged velocity fluctuation fields of the jet flow in a ross-stream 59hapter 8 Flow patterns of a row of jets in a cross-stream 64-1 The jet flow pattern in a cross-stream 64-2 The cross-stream flow pattern passed through a row of jets 71hapter 9 Conclusions and Recommendations 75eferences 81igures 856094856 bytesapplication/pdfen-US主流場內噴流質點影像測速儀流場可視化反轉渦漩流對三維流線Jets in a cross-streamPIVFlow visualizationCVPLift-off3D streamlinethesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/187017/1/ntu-96-D89522003-1.pdf