本研究探討衝擊噴流在橫風中的流場特性。實驗在一部自行設計的閉迴路風洞中進行，使用雷射光頁輔助煙霧流場可視化技術(Laser Light-Sheet Assisted Smoke Flow Visualization Technique)觀察衝擊噴流在橫風中之流場特性，並以質點影像速度儀(Particle Image Velocimeter, PIV)量測流場對稱面的速度分布。主要參數為觀察到的噴流雷諾數範圍內的噴流對橫風速度比。流動可視化聚焦於觀測噴流與壁面衝擊並受橫風影響時，流場結構的特徵模態；速度場量測聚焦於流動可視化所獲得特徵模態的量化分析，包括：流動拓樸分析、渦度及紊流強度分布。受橫風影響之衝擊噴流的流場特徵模態，包括：無衝擊噴流(No Impingement)、輕微衝擊噴流(Slight Impingement)、單渦旋(Single Vortex)以及過度模態(Trasition)。這四種模態呈現在噴流對橫流速度比R與噴流類諾數Rej域面不同的區域：在很低R時( R < 2.1)，產生無衝擊噴流模態；在2.1 < R < 3.8時，出現輕微衝擊噴流；在3.8 < R < 13.5時，產生單渦旋模態，在衝擊噴流上游緊貼壁面出現單一顆穩定渦旋；在R > 13.5時，在衝擊噴流上游緊貼壁面附近大部分時間會出現如單渦旋模態的大渦旋，但有時會在此一大渦旋的上游產生一顆小的引致渦旋。出現在單渦旋與過度模態中，位於衝擊噴流上游緊貼壁面的單一渦旋與引致小渦旋具有特別高的紊流強度與渦度。

The study investigated the flow characteristics of impinging jets in crossflow by experimental methods. Experiments were conducted in a self-designed close-returned wind tunnel. The laser-light sheet assisted smoke flow visualization technique was used to observe the flow patterns for qualitative analysys. The Particle Image Velocimetry (PIV) was used to measure the velocity distributions in the symmetric plane of the flow field. The primary parameter dominating the flow patterns was the jet-to-crossflow velocity ratio R within the range of range of the observed jet Reynolds number Rej. The PIV measured velocity data were analyzed to obtaine the streamline flow patterns, topological flow structures, vorticities, and turbulence intensities. Four characteristic flow patterns were identified from the recorded video clips and pictures, they are no impingement, slight impingement, single vortex, and transition. The no impingement mode appeared at the very low velocity ratios R < 2.1. The slight impingement mode was found at 2.1 < R < 3.8. The single vortex and transition modes were observed in the ranges of 3.8 < R < 13.5 and R > 13.5, respectively. A single vortex appeared around the upwind side of the jet impinging region, and therefore was denoted as the single vortex mode. The size of the vortex increased with increasing the jet-to-crossflow velocity ratio. In the transition mode, a small vortex was induced occasionally downstream the primary large single vortex due to the increased jet-to-crossflow velocity ratio. High turbulence intensities and large vorticities were found around the areas of the primary and induced vortices.

[1] Wang, X. K., Niu, G.-P., Yuan, S.-Q., Zheng, J. X., and Tan, S. K., “Experimental investigation on the mean flow field and impact force of a semiconfined round impinging jet,” Fluid Dynamics Research, Vol. 47, No. 2, 2015.
[2] Bradshaw, B. A., and Edna, M. Love., “The normal impingement of a circular air jet on a flat surface,” Reports and Memoranda, No. 3205, 1959.
[3] Landreth, C. C., and Adrian, R. J., “Impingement of a low Reynolds number turbulent circular jet onto a flat plate at normal incidence,” Experiments in Fluids, No. 9, 1990, pp. 74-84.
[4] Myszko, M., and Knowles, K., “Development of a wall jet from an impinging, round turbulent, compressible jet,” AIAA Fluid Dynamics Conference, 1994, pp. 1-7.
[5] Koichi Nishino., Masanori Samada., Keiichi Kasuya, and Kahoru Torii., “Turbulence statistics in the stagnation region of an axisymmetric impinging jet flow,” International Journal of Heat and Fluid Flow, Vol. 17, No. 3, 1996, pp. 193-201.
[6] Lee, D. H., Chung, Y. S., and Kim, D. S., “Turbulent flow and heat transfer measurements on a curved surface with a fully developed round impinging jet,” Int. J. Heat and Fluid Flow, Vol. 18, No. 1, 1997, pp. 160-169.
[7] Fleischer, A. S., Kramer, K., Goldstein, R. J., “Dynamics of the vortex structure of a jet impinging on a convex surface,” Experimental Thermal and Fluid Science, Vol. 24, No. 3-4, 2001, pp. 169-175.
[8] O'Donovan, T. S., Murray, D. B., Torrance, A. A., “Jet heat transfer in the vicinity of a rotating grinding wheel,” J. Mechanical Engineering Science, Vol. 220, No. 6, 2006, pp. 837-845.
[9] Attalla, M., Hussein, M., and Specht, E., “Effect of inclination angle of a pair of air jets on heat transfer into the flat surface,” Experimental Thermal and Fluid Science, Vol. 85, 2017, pp. 85-94.
[10] Beltaos, S., “Oblique impingement of circular turbulent jets,” Journal of Hydraulic Research, Vol. 14, No. 1, 1976, pp. 17-36.
[11] Fan, J. Y., Yan, Z., and Wang, D. Z., “Experimental study on the vortex formation and entrainment characteristics for a round transverse jet in shallow water,” Journal of Hydrodynamics, Vol. 21, No. 3, 2009, pp. 386-393.
[12] Barata, J. M. M., Durao, D. F. G., Heitor, M. V., and McGuirk, J. J., “On the analysis of an impinging jet on ground effects,” Experiments in Fluids, Vol. 15, No. 2, 1993, pp. 117-129.
[13] Barata, J. M. M., and Durao, D. F. G., “Laser-Doppler measurements of impinging jet flows through a crossflow,” Experiments in Fluids, Vol. 36, No. 5, 2004, pp. 665-674.
[14] Barata, J. M. M., Ribeiro, S., Santos, P., and Silva, A. R. R., “Experimental study of a ground vortex,” Journal of Aircraft, Vol. 46, No. 4, 2009, pp. 1152-1159.
[15] Dennis, R. F., Tso, J., and Margason, R. J., “induced Surface Pressure Distribution of a Subsonic Jet in a Crossflow,” AIAA Fluid Dynamics Conference, 1994, pp. 1-9.
[16] Nakabe, K., Inaoka, K., Ai, T., and Suzuki, K., “Flow visualization of longitudinal vortices induced by an inclined impinging jet in a crossflow—effective cooling of high temperature gas turbine blades,” Energy Conversion and Management, Vol. 38, No. 10-13, 1997, pp. 1145-1153.
[17] Chenglong, W., Lei, L., Lei, W., and Bengt, S., “Heat transfer and fluid flow of a single jet impingement in Crossflow modified by a vortex generator pair,” American Society of Mechanical Engineers (ASME), 2016, pp. 1-8.
[18] Flagan, R. C., and Seinfeld, J. H., Fundamentals of air pollution engineering. Prentice Hall, Engle wood Cliffs, New Jersey, 1988.
[19] Baker, C., “The turbulent horseshoe vortex,” Journal of Wind Engineering and Industrial Aerodynamics, Vol. 6, No. 1-2, 1980, pp. 9-23.
[20] Perry, A., and Fairlie, B., “Critical points in flow patterns,” Advances in geophysics, Vol. 18, Part B, 1975, pp. 299-315.
[21] Perry, A., Chong, M., and Lim, T., “The vortex-shedding process behind two-dimensional bluff bodies,” Journal of Fluid Mechanics, Vol. 116, 1982, pp. 77-90.
[22] Steiner, T., and Perry, A., “Large-scale vortex structures in turbulent wakes behind bluff bodies. Part 2. Far-wake structures,” Journal of Fluid Mechanics, Vol. 174, 1987. pp. 271-298.
[23] Hunt, J. C. R., Abell, C. J., Peterka, J. A., and Woo, H., “Kinematical studies of the flows around free or surface-mounted obstacles; applying topology to flow visualization,” Journal of Fluid Mechanics, Vol. 86, No. 1, 1978, pp. 179-200.