本研究針對一在橫風環境中的圓管噴流，以實驗方法探討後傾角度對特徵流場行為特徵與混合特性的影響。藉由雷射光頁輔助之煙霧流場觀察技術擷取瞬時與長時間曝光的流場影像；利用熱線風速儀偵測剪流層的頻率特徵；應用高速質點影像速度儀量測時間平均的速度向量場；使用追蹤氣體濃度測試法診斷噴流在橫風環境中的消散情況。本研究的後傾角度變化由0o至60o。分析瞬間與長時間曝光的流場照片，在噴流對應橫風之動量通量比對後傾角的域面上，噴流迎風面剪流層渦漩可劃分出五種特徵模態，分別是「混合層型式渦漩」、「背向滾轉渦漩」、「背向滾轉渦漩」、「蕈狀渦漩」與「噴流型式渦漩」。在後傾角低於25o時，在尾流區形成一個大的下洗迴流泡，隨著後傾角增加，流泡的尺寸迅速變小。在後傾角大於25o時，在尾流區的下洗迴流泡消失。噴流的寬度隨著後傾角的增加而變小。噴流迎風面剪流層之渦漩結構的史卓數，隨著後傾角增加而降低。在固定的後傾角條件下，當噴流對應橫風之動量通量比小於1時，史卓數隨著噴流對應橫風之動量通量比的增加而明顯地增加；而當噴流對應橫風之動量通量比小於1時，史卓數隨著噴流對應橫風之動量通量比增加而增加的幅度變小。藉由分析時間平均的速度場，在噴流對應橫風之動量通量比對後傾角的域面上，偏析噴流的流場特徵，可以區分成四個模態，分別為「噴流尾流渦漩」、「逆向流動」、「圓管尾流渦漩」及「同向流動」。在噴流尾流渦漩與逆向流動模態，噴流靠近尾流區域之噴流尾流渦漩及分歧線引致強烈的噴流與橫風互相捲入。因此，在靠近偏折噴流的尾流區產生較大的紊流強度。由追蹤氣體量測的結果發現，在噴流尾流渦漩及逆向流動模態的偏折噴流，比在圓管尾流渦漩與同向流動模態的偏折噴流，有較佳的擴散特性，此噴流擴散的增強，主要是受到尾流區之噴流尾流渦漩及分歧線引致強烈的噴流與橫風互相捲入所導致的效應。

The effects of backward inclination angle θ on the flow and mixing characteristics of the transverse jets were studied experimentally in an open-loop wind tunnel. The instantaneous and long-exposure flow pictures of the transverse jets were captured by laser-assisted smoke flow visualization method. The frequency characteristics of the upwind-side shear layer were measured by a hot-wire anemometer. The time-averaged velocity vector fields of the transverse jet were measured by high-speed particle image velocimetry. The jet dispersion characteristics were detected by tracer gas detection technique. The backward inclined angles were varied from 0o to 60o. Five upwind-side shear-layer vortex modes (mixing-layer type vortices, backward-rolling vortices, forward-rolling vortices, mushroom vortices, and jet-type vortices) were identified from instantaneous and long-exposure pictures in the domain of R and θ. At θ < 25o, large downwash recirculation bubble appeared in the wake region. Increasing θ would quickly decrease the size of the downwash recirculation bubble. At θ > 25o, no downwash recirculation bubble was observed in the near wake of the tube tip region. The jet width decreased with increasing θ. The Strouhal number of the upwind-side vortices increased with increasing θ. At a fixed θ, the Strouhal number of the upwind-side vortices decreased drastically with increasing R at R < 1. At R > 1, the decrease rate became small. Four characteristic flow modes, jet-wake vortex, reverse flow, tube-wake vortex, and co-flow, were classified in the domain of R and θ by observing the time-averaged velocity fields. At the jet-wake vortex and reverse flow modes, the transverse jets in the near wake region exhibited large turbulence intensities because the jet-wake vortex and bifurcation lines induced significant entrainment between jet fluid and crossflow. The results of tracer gas concentration distributions revealed that the bent jet fluid at jet-wake vortex and reverse flow modes had better dispersion than those at tube-wake vortex and co-flow modes because of the entrainment effect of the jet-wake vortex and bifurcation lines.

[1]E. Farvardin, M. Johnson, H. Alaee, A. Martinez, A. Dolatabadi, Comparative study of biodiesel and diesel jets in gaseous crossflow, Journal of Propulsion and Power, 29 (2013) 1292-1302.
[2]P. Luo, H. Jia, C. Xin, G. Xiang, Z. Jiao, H. Wu, An experimental study of liquid mixing in a multi-orifice-impinging transverse jet mixer using PLIF, Chemical Engineering Journal, 228 (2013) 554–564.
[3]S.N. Mahjoub, S. Habli, H. Bournot, G.L. Palec, The near field in the mixing of a three-dimensional inclined pollutant jet with a crossflow, Journal of Enhanced Heat Transfer, 19 (2012) 161-178.
[4]R.J. Fawcett, A.P.S. Wheeler, L. He, R. Taylor, Experimental investigation into the impact of crossflow on the coherent unsteadiness within film cooling flows, Journal of Heat and Fluid Flow, 40 (2013) 32–42.
[5]I. Nastase, A. Meslem, M.E. Hassan, Image processing analysis of vortex dynamics of lobed jets from three-dimensional diffusers, Fluid Dynamics Research, 43 (2011) 065502.
[6]W. Mikolowsky, H. McMahon, An experimental investigation of a jet issuing from a wing in crossflow, Journal of Aircraft, 10 (1973) 546-553.
[7]J.E. Gardner, A. Burgisser., P. Stelling, Eruption and deposition of the Fisher Tuff (Alaska): Evidence for the evolution of pyroclastic flows, Journal of Geology, 115 (2007) 417-436.
[8]J. Foust, D. Rockwell, Flow structure associated with multiple jets from a generic catheter tip, Experiments in Fluids, 42 (2007) 513-530.

[9]L. Cortelezzi, A.R. Karagozian, On the formation of the counter-rotating vortex pair in transverse jets, Journal of Fluid Mechanics, 446 (2001) 347-373.
[10]Z.M. Moussa, J.W. Trischka, S. Eskinazi, The near field in the mixing of a round jet with a cross-stream. Journal of Fluid Mechanics, 80 (1977) 49-80.
[11]J. Andreopoulos, Wind tunnel experiments on cooling tower plumes, part I: in uniform cross flow, American Society of Mechanical Engineers, ASME Paper 86-WA/HT-31, 1986.
[12]J. Andreopoulos, Wind tunnel experiments on cooling tower plumes, part II: in non-uniform cross flow of boundary layer type, American Society of Mechanical Engineers, ASME Paper 86-Wa/Ht-32, 1986.
[13]O.S. Eiff, J.G. Kawall, J.F. Keffer, Lock-in of vortices in the wake of an elevated round turbulent jet in a crosswind, Experiments in Fluids, 19 (1995) 203-213.
[14]O.S. Eiff, J.F. Keffer, On the structures in the near-wake region of an elevated turbulent jet in a crossflow, Journal of Fluid Mechanics, 333 (1997) 161-195.
[15]S.H. Smith, M.G. Mungal, Mixing, structure and scaling of the jet in crossflow, Journal of Fluid Mechanics, 357 (1998) 83-122.
[16]R.F. Huang, R.H. Hsieh, Sectional flow structures in near wake of elevated jets in a crossflow, AIAA Journal, 41 (2003) 1490-1499.
[17]L.K. Su, M.G. Mungal, Simultantaneous measurements of scalar and velocity field evolution in turbulent crossflowing jets, Journal of Fluid Mechanics, 513 (2004) 1-45.
[18]R.F. Huang, J. Lan, Characteristic modes and evolution processes of shear-layer vortices in an elevated transverse jet, Physics of Fluids, 17 (2005) 1-13.
[19]D.R. Getsinger, C. Hendrickson, A.R. Karagozian, Shear layer instabilities in low-density transverse jets, Experiments in Fluids, 53 (2012) 783–801.
[20]Z.U. Khan, J.P. Johnston, On vortex generating jets, International J. Heat Mass Flow, 21 (2000) 506-511.
[21]M.I. Yaras, Measurements of surface-roughness effects on the development of a vortex produced by an inclined jet in cross-flow, Journal Fluids Engineering, 126 (2004) 346-126.
[22]W. Jessen, W. Schröder, M. Klaas, Evolution of jets effusing from inclined holes into crossflow, Internation J. Heat and Fluid Flow, 28 (2007) 1312-1326.
[23]L.M. Wright, S.T. McClain, M.D. Clemenson, Effect of freestream turbulence intensity on film cooling jet structure and surface effectiveness using PIV and PSP, J. Turbomachinery, 133 (2011) 041023-1~041023-12.
[24]S.N. Mahjoub, S. Habli, H. Bournot, G.L. Palec, The near field in the mixing of a three-dimensional inclined pollutant jet with a crossflow, Journal of Enhanced Heat Transfer, 19 (2012) 161-178.
[25]F. Coletti, C.J. Elkins, J.K. Eaton, An inclined jet in crossflow under the effect of streamwise pressure gradients, Experiments in Fluids, 54 (2013) 1432-1114.
[26]H.C. Vincent, M. Asce, Oblique turbulent jets in crossflow, Journal of Engineering Mechanics, 111 (1985) 1343-1360.
[27]L.V. Sergio Coelho, J.C.R. Hunt, The dynamics of the near field of strong jets in crossflow, Journal of Fluid Mechanics, 200 (1989) 95-120.
[28]H. Donghee, V. Orozco, M.G. Mungal, Gross-entrainment behavior of turbulent jets injected obliquely into a uniform crossflow, AIAA Journal, 38 (2000) 1643-1649.
[29]E.F. Hasselbrink JR, M.G. Mungal, Transverse jets and jet flames. Part 2. Velocity and OH field imaging, Journal of Fluid Mechanics, 443 (2001) 27-68.
[30]D. Han, M.G. Mungal, Simultaneous measurement of velocity and CH distribution. Part II: deflected jet flames, Combustion and Flame, 133.1 (2003) 1-17.
[31]G.A. Kikkert, M.J. Davidson, R.I. Nokes, A jet at an oblique angle to a cross-flow, Journal of Hydro-environment Research, 3 (2009) 69-76.
[32]S. Sundararaj, V. Selladurai, Numerical and experimental study on jet trajectory and mixing behavior of venturi-jet mixer,” Journal of Fluids Engineering, 132 9 (2010) 1-9.
[33]M.S. Adaramola, D. Sumner, D.J. Bergstrom, Turbulent wake and vortex shedding for a stack partially immersed in a turbulent boundary layer, Journal of Fluids and Structures, 23 (2007) 1189-1206.
[34]R. Camussi, G. Guj, A. Stella, Experimental study of a jet in a crossflow at very low Reynolds number, Journal of Fluid Mechanics, 454 (2002) 113-144.
[35]R.F. Huang, R.H. Hsieh, Sectional flow structures in near wake of elevated jets in crossflow, AIAA Journal, 41 (2003) 1490-1499.
[36]R.F. Huang, R.H. Hsieh, An experimental study of elevated round jets deflected in a crosswind, Experimental Thermal and Fluid Science, 27 (2002), 77-86.
[37]R.C. Flagan, J.H. Seinfield, Fundamentals of Air Pollution Engineering, Prentice Hall, Englewood Cliffs, New Jersey, (1988) 290-357.
[38]R. Mie, Velocity Fidelity of Flow Tracer Particles, Experiments in Fluids, 22 (1996) 1-13.
[39]B. Poornima, Y. Ramadevi, T. Sridevi, Threshold based edge detection algorithm, IACSIT International Journal of Engineering and Technology, 3.4 (2011) 400.
[40]L.G. Shapiro, G.C. Stockman, Computer Vision, Prentice Hall, Upper Saddle River, New Jersey, 2001.
[41]R.D. Keane, R.J. Adrian, Optimization of particle image velocimeters Part I: double pulsed systems, Measurement Science and Technology, 1.11 (1990) 1202-1215.
[42]R.D. Keane, R.J. Adrian, Theory of Cross-correlation Analysis of PIV Images, Applied Scientific Research, 49 (1992) 191-215.
[43]D.P. Hart, PIV error correction, Experiments in Fluids, 29 (2000)13-22.
[44]W.G. Steele, R.P. Taylor, R.E. Burrell, H.W. Coleman, Use of previous experience to estimate precision uncertainty of small sample experiments, AIAA Journal, 31.10 (1993) 1891-1896 .
[45]R.J. Moffat, Describing the uncertainties in experimental results, Journal of Experimental Thermal and Fluid Science, 1 (1988) 3-17.
[46]E. Lazer, B. DeBlauw, N. Glumac, C. Dutton, G. Elliott, A practical approach to PIV uncertainty analysis, 27th AIAA Aerodynamic Measurement Technology and Ground Testing Conference, Chicago, Illinois, (2010) 4355.
[47]R.F. Huang, R.H. Hsieh, Sectional flow structures in near wake of elevated jets in a crossflow, AIAA Journal, 41 (2003) 1490-1499.
[48]R.F. Huang, J. Lan, Characteristic modes and evolution processes of shear-layer vortices in an elevated transverse jet, Physics of Fluids, 17 (2005) 1-13.
[49]C.D. McGillem, G.R. Cooper, Continuous and Discrete Signal and System Analysis, second ed., Holt, Rinehart and Winston, New York, 1984.
[50]A.J. Yule, Large-scale structure in the mixing layer of a round jet, Journal of Fluid Mechanics, 89 (1978) 413-432.
[51]M.J. Lighthill, Attachment and separation in three-dimensional flow, in Rosenhead, L. (editor.) Laminar Boundary Layers, Oxford University Press, Cambridge, (1963) 72-82.
[52]J.Z. Holland, A meteorological survey of the oak ridge area, U.S. Atomic Energy Commission Report, ORO-99, (1953).
[53]E.F. Hasselbrink, M.G. Mungal, Transverse jets and jet flames. Part 1. Scaling laws for strong transverse jets, Journal of Fluid Mechanics, 443 (2001) 1-25.
[54]R.J. Margason, The path of a jet directed at large angles to a subsonic free stream, Tech. Rep. TN D-4919 NASA, (1968).
[55]B.D. Pratte, W.D. Baines, Profiles of the round turbulent jet in a cross flow, Journal of Hydraulics Division, (1967) 53-64.
[56]L.L. Yuan, R.L. Street, Trajectory and entrainment of a round jet in crossflow, Physics of Fluids, 10.9 (1998) 2323.
[57]J.F. Foss, Interaction region phenomena for the jet in a cross-flow problem, Rep. SFB 80/E/161, University of Karlsruhe, (1980).
[58]T. Kawamura, M. Hiwada, T. Hibino, I. Mabuchi, M. Kumada, Flow around a finite circular cylinder on a flat plate: Cylinder height greater than turbulent boundary layer thickness, Bulletin of JSME, 27.232 (1984) 2142-2151.