Near wake structure behind a 3D square prism with the aspect ratio of 2.7 in a shallow boundary layer flow

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• 作者：Hiromasa Kawai^a ; ^{kawai813@mail.dendai.ac.jp} ; Yasuo Okuda^b ; Masamiki Ohashi^b
• 关键词：3D square prism ; Shallow boundary layer ; 2D PIV ; 3D-stereoscopic PIV ; Unsteady wake ; Ká ; rmá ; n vortex ; Arch-type vortex ; Conditional image sampling ; POD analysis
• 刊名：Journal of Wind Engineering and Industrial Aerodynamics
• 出版年：2012
• 期刊代码：55_01676105
• 类别：ms
• 出版时间：May-July, 2012
• 卷：104-106
• 期：Complete
• 页码：196-202
• 文件大小：2679 K

摘要

Three dimensional structures of unsteady flows behind a square prism with aspect ratio H/D=2.7 in a shallow boundary layer flow are investigated by two dimensional and three dimensional stereoscopic PIV techniques synchronizing with velocity measurement by a hot wire anemometer. According to the conditional PIV image sampling technique conducted by using the velocity signal measured outside the separated shear layer, it becomes clear that an arch-type vortex is formed behind the prism throughout a cycle of the K谩rm谩n vortex formation and shedding. As the vortex grows and moves downstream, the vortex line stretches in a stream-wise direction near the tip of the vortex which does not move and stays still just behind the prism throughout a cycle. According to POD analysis, the wake fluctuates very slowly with a period of approximately 6 times of that of the K谩rm谩n vortex shedding.