本研究針對一在橫風環境中受聲波激擾之圓管噴流，以實驗方法探討特徵流場行為的衍化過程、噴流擴散、混合性能及紊流特性。使用一揚聲器作為噴流的聲波激擾裝置。藉由雷射光頁輔助之煙霧流場觀察技術搭配高速攝機擷取瞬時流場影像;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的凝序性結構進行速度及特徵頻率診斷;透過影像邊界辨識技術取得橫風噴流的擴散高度及擴散寬度;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。應用高速質點影像速度儀量測流場速度。分析噴流在橫風環境中的流場結構之連續衍化照片，在噴流對應橫風之動量通量比對聲波激擾史卓數的域面，可劃分出三種流場的特徵模態，分別是「同步擺動噴流」、「過渡」與「同步剪流層渦漩」。在同步擺動噴流模態時，靠近噴流管口的噴流氣柱呈現週期性地前後擺動運動，導致受偏折之後的噴流在橫風中大幅度的上下振動，且擺動頻率與聲波激擾頻率相同。相較於未受激擾的橫風噴流，聲波激擾明顯地增加噴流的擴散及混合的效果。在過渡及同步剪流層渦漩模態時，一個渦漩會在噴流的迎風面之剪流層上形成，再進行衍化。在同步剪流層渦漩模態，渦漩頻率與聲波激擾頻率相同;然而，在過渡模態時，渦漩頻率不受聲波激擾所支配。在過渡及同步剪流層渦旋模態中，噴流擴散及混合的效果較不顯著，因為剪流層渦漩結構造成的擴散效應比同步擺動噴流模態中的氣柱擺動小。未受激擾的橫風噴流之時間平均的速度向量及流線圖顯示噴流離開管口後，受到橫風的衝擊，明顯地偏折。當噴流受聲波激擾，在同步擺動噴流模態時，特別在共振的情況之下具有較大的噴流動量支撐橫風的衝擊，故噴流氣柱在橫風中的偏折較小。因此，噴流受聲波激擾在共振條件時，產生最高的噴流軌跡及最大的噴流擴散效果。針對流場的紊流特性，利用統計分析方法將速度資料轉換紊流強度、渦度、紊流剪應力、特徵時間尺度與特徵長度尺度，本文亦呈現聲波激擾對紊流特性的影響。

Flow-evolution processes, as well as the penetration, spread, and dispersion characteristics, and the turbulent flow field of stack-issued pulsating transverse jets were studied experimentally in a wind tunnel. Jet pulsations were generated by means of acoustic excitation. Streak pictures of the smoke-flow patterns, illuminated by a laser-light sheet in the median plane, were recorded by a high-speed digital camera. A hot-wire anemometer was used to digitize instantaneous velocities of instabilities in the flow. Penetration height and spread width were obtained through a binary edge identification technique. Tracer-gas concentrations were measured to provide information on jet dispersions. A high-speed particle image velocimeter (PIV) was employed to measure the velocity field. Three characteristic flow modes (synchronized flapping jet, transition, and synchronized shear-layer vortices) were identified in the domain of the jet-to-crossflow momentum flux ratio and the excitation Strouhal number. In the synchronized flapping jet mode, the jet column near the tube exit flapped back-and-forth periodically at the excitation frequency, and induced large up-down motions of the deflected jet. The penetration, spread, and dispersion of the jet increased drastically compared with the non-excited jet. Forcing the jet into the transition and synchronized shear-layer vortices regimes caused the vortices to appear along the upwind shear layer of the deflected jet. Under these conditions, the penetration, spread, and dispersion of the jet presented insignificant increases because the entrainment effect induced by the shear-layer vortices was not as large as that produced by the jet oscillating motions in the synchronized flapping jet regime. The time-averaged velocity vectors and streamline patterns of the non-excited transverse jet exhibited fast deflection due to the impingement of the crossflow. As the transverse jet was excited in the synchronized flapping jet mode, particularly at the resonance frequency, the jet shot to high altitude and was drastically less deflected than the non-excited transverse jet. Therefore, the excited transverse jet at resonance condition produced the highest jet trajectory and largest jet penetration and spread. The turbulence intensities, vorticities, and turbulent shear stress of the excited transverse jet exhibited dramatically higher values than those of the non-excited transverse jet. Lagrangian integral time and length scales of the transverse jet excited at the resonance condition were drastically smaller than those of the non-excited one.

[1] Pratte, B. D. and Baines, W. D., “Profiles of the Round Turbulent Jet in a Crossflow ,” Journal of Hydraulics Division ASCE, Vol. 93, 1967, pp. 53-64.
[2] Kamotani, Y. and Greber, I., “Experiments on a Turbulent Jet in a Crossflow,” AIAA Journal, Vol. 10, No. 11, 1972, pp. 1425-1429.
[3] Andreopoulos, J., “On the Structure of Jets in a Crossflow,” Journal of Fluid Mechanics, Vol. 157, 1985, pp. 163-197.
[4] Fric, T. F. and Roshko, J., “Vortical Structure in the Wake of a Transverse Jet,” Journal of Fluid Mechanics, Vol. 279, 1994, pp. 1-47.
[5] Kelso, R. M., Lim, T. T., and Perry, A. E., “An Experimental Study of Round Jets in Cross-Flow,” Journal of Fluid Mechanics, Vol. 306, 1996, pp. 111-144.
[6] Smith, S. H. and Mungal, M. G., “Mixing, Structure and Scaling of the Jet in Crossflow,” Journal of Fluid Mechanics, Vol. 357, 1998, pp. 83-122.
[7] Su, L. K., and Mungal, M. G., “Simultaneous Measurements of Scalar and Velocity Field Evolution in Turbulent Crossflowing Jet,” Journal of Fluid Mechanics, Vol. 513, 2004, pp.1-45.
[8] Andreopoulos, J., “Wind Tunnel Experiments on Cooling Tower Plumes, Part I: In Uniform Crossflow,” ASME Paper 86-WA/HT-31, 1986, pp. 7-12.
[9] Andreopoulos, J., “Wind Tunnel Experiments on Cooling Tower Plumes, Part II: In Non-Uniform Crossflow of Boundary Layer Type,” ASME Paper 86-WA/HT-32, 1986, pp. 1-17.
[10] Eiff, O. S., Kawall, J. G., and Keffer, J. F., “Lock-In of Vortices in the Wake of an Elevated Round Turbulent Jet in a Crosswind,” Experiment in Fluids, Vol. 19, 1995, pp. 203-213.
[11] Huang, R. F. and Hsieh, R. H., “An Experimental Study of Elevated Round Jets Deflected in Crosswind,” Experimental Thermal and Fluid Science, Vol. 27, No. 3, 2002, pp. 77-86.
[12] Huang, R. F. and Hsieh, R. H., “Sectional Flow Structures in Near Wake of Elevated Jets in a Crossflow,” AIAA Journal, Vol. 41, No. 8, 2003, pp. 1490-1499.
[13] Huang, R. F. and Lan, J., “Characteristic Modes and Evolution Processes of Shear-Layer Vortices in an Elevated Transverse Jet,” Physics of Fluids, Vol. 17, No. 3, 2005, 1-13.
[14] Vermeulen, P. J., Chin, C.-F., and Yu, W. K., “Mixing of an Acoustically Pulsed Air Jet with a Confined Crossflow,” Journal of Propulsion and Power, Vol. 6, No. 6, 1990, pp. 777-783.
[15] Vermeulen, P. J., Grabinski, P., and Ramesh, V., “Mixing of an Acoustically Excited Air Jet with a Confined Hot Crossflow,” Journal of Engineering for Gas Turbines and Power, Vol. 114, 1992, pp. 46-54.
[16] M’Closkey, R. T., King, J. M., Cortelezzi, L., and Karagozian, A. R., “The Actively Controlled Jet in Crossflow,” Journal of Fluid Mechanics, Vol. 452, 2002, pp. 325-335.
[17] Shapiro, S. R., King, J., M’Closkey, R. T., and Karagozian, A. R., “Optimization of Controlled Jets in Crossflow,” AIAA Journal, Vol. 44, No. 6, 2006, pp. 1292-1298.
[18] Gogineni, S., Goss, L., and Roquemore, M., “Manipulation of a Jet in a Cross Flow,” Experimental Thermal and Fluid Science, Vol. 16, 1998, pp. 209-219.
[19] Chang, Y. K. and Vakili, A. D., “Dynamics of Vortex Rings in Crossflow,” Physics of Fluids, Vol. 7, No. 7, 1995, pp. 1583-1597.
[20] Hermanson, J. C., Wahba, A., and Johari, H., “Duty-Cycle Effects on Penetration of Fully Modulated, Turbulent Jet in Crossflow,” AIAA Journal, Vol. 36, No. 10, 1998, pp. 1935-1937.
[21] Johari, H., Pacheco-Tougas, M., and Hermanson, J. C., “Penetration and Mixing of Fully Modulated Turbulent Jets in Crossflow,” AIAA Journal, Vol. 37, Vo. 7, 1999, pp. 842-850.
[22] Eroglu, A. and Breidenthal R. E., “Structure, Penetration, and Mixing of Pulsed Jet in Crossflow,” AIAA Journal, Vol. 39, No. 3, 2001, pp. 417-423.
[23] Johari, H., “Scaling of Fully Pulsed Jets in Crossflow,” AIAA Journal, Vol. 44, No. 11, 2006, pp. 2719-2725.
[24] Megerian, S., Davitian, J., Alves, L. S. de B., and Karagozian, A. R., “Transverse-Jet Shear-Layer Instabilities. Part 1. Experimental Studies,” Journal of Fluid Mechanics, Vol. 593, 2007, pp. 93-129.
[25] Davitian, J., Hendrickson, C., Getsinger, D., M’Closkey, R. T., and Karagozian, A. R., “Strategic Control of Transverse Jet Shear Layer Instabilities,” AIAA Journal, Vol. 48, No. 9, 2010, pp. 2145-2156.
[26] Ginversky, A. S., Valsov, Y. V., and Karavosov, R. K., Acoustic Control of Turbulent Jet, Springer-Verlag, Berlin, 2004.
[27] Shames, I. H., Mechanics of Fluid, Third ed., McGraw-Hill, Singapore, 1992.
[28] Flagan, R. C. and Seinfield, J. H., Fundamentals of Air Pollution Engineering, Prentice Hall, Englewood Cliffs, New Jersey, 1988, pp. 290-357.
[29] Mie, R., “Velocity Fidelity of Flow Tracer Particles,” Experiments in Fluids, Vol. 22, 1996, pp. 1-13.
[30] Shapiro, L. G. and Stockman, G. C., Computer Vision, Prentice Hall, Upper Saddle River, New Jersey, 2001.
[31] Anchini, R., Liguori, C., and Paolillo, A., “Evaluation of Uncertainty of Edge-Detector Algorithms,” IEEE Transaction on Instrumentation and Measurement, Vol. 56, No. 3, 2007, pp. 681-688.
[32] Keane, R. D. and Adrian, R. J., “Theory of Cross-correlation Analysis of PIV Images,” Applied Scientific Research, Vol. 49, No. 3, 1992, pp. 191-215.
[33] Keane, R. D. and Adrian, R. J., “Optimization of Particle Image Velocimeters Part I: Double Pulsed Systems,” Measurement Science and Technology, Vol. 1, No. 11, 1990, pp. 1202-1215.
[34] Huang, R. F. and Chang, K. T., “Evolution and Turbulence Properties of Self-Sustained Transversely Oscillating Flow Induced by Fluidic Oscillator,” Journal of Fluids Engineering, ASME Transactions, Vol. 129, 2007, pp. 1038-1047.
[35] Kinsler, L. E. and Frey A. R., Fundamentals of Acoustics, Second ed., Wiley, New York, 1982.
[36] Johari, H., Zhang, M. J., and Bourque, S. M., “Impulsively Started Turbulent Jets,” AIAA Journal, Vol. 35, No. 4, 1997, pp. 657-662.
[37] Gharib, N., Rambod, E., and Shariff, K., “A Universal Time Scale for Vortex Ring Formation,” Journal of Fluid Mechanics, Vol. 360, 1998, pp. 121-140.
[38] Tennekes, H. and Lumley, J. L., A First Course in Turbulence, MIT Press, Cambridge, 1972, pp. 248-261.
[39] Tritton, D. J., Physical Fluid Dynamics, Oxford University Press, Oxford, 1988, pp. 123-151.
[40] Pope, S. B., Turbulent Flows, Cambridge University Press, Cambridge, 2000.
[41] Huang, R. F. and Lin, C. L., “Flow Characteristics and Shear-Layer Vortex Shedding of Double Concentric Jets,” AIAA Journal, Vol. 35, No. 5, 1997, pp. 887-892.
[42] Huang, R. F. and Lee, H. W., “Turbulence Effect on Frequency Characteristics of Unsteady Motions in Wake of Wing,” AIAA Journal, Vol. 38, No. 1, 2000, pp. 87-94.
[43] Zaman, K. B. M. Q. and Hussain, A. K. M. F., “Taylor Hypothesis and Large-Scale Coherent Structures,” Journal of Fluid Mechanics, Vol. 112, 1981, pp. 379-396.