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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Von Kármán vortex street ： ウィキペディア英語版 Kármán vortex street In fluid dynamics, a Kármán vortex street (or a von Kármán vortex sheet) is a repeating pattern of swirling vortices caused by the unsteady separation of flow of a fluid around blunt bodies. It is named after the engineer and fluid dynamicist Theodore von Kármán,〔Theodore von Kármán, ''Aerodynamics''. McGraw-Hill (1963): ISBN 978-0-07-067602-2. Dover (1994): ISBN 978-0-486-43485-8.〕 and is responsible for such phenomena as the "singing" of suspended telephone or power lines, and the vibration of a car antenna at certain speeds. ==Analysis== A vortex street will only form at a certain range of flow velocities, specified by a range of Reynolds numbers (''Re''), typically above a limiting ''Re'' value of about 90. The Reynolds number is a measure of the ratio of inertial to viscous forces in the flow of a fluid and may be defined as: :$\backslash mathrm=\backslash frac\backslash$ where: *$d$ = the diameter of the cylinder (or some other suitable measure of width of non-circular bodies) about which the fluid is flowing. *$V$ = the steady velocity of the flow upstream of the cylinder. *$\backslash nu\backslash ,$ = the kinematic viscosity of the fluid. or: :$\backslash mathrm=\backslash frac$ where: *$\backslash rho\; \_\backslash infty$ = the free stream fluid density. *$V\; \_\backslash infty$ = the steady free stream velocity of the flow upstream of the cylinder. *$d$ = the diameter of the cylinder (or some other suitable measure of width of non-circular bodies) about which the fluid is flowing. *$\backslash mu\; \_\backslash infty$ = the free stream dynamic viscosity of the fluid. The range of ''Re'' values will vary with the size and shape of the body from which the eddies are being shed, as well as with the kinematic viscosity of the fluid. Over a large ''Re'' range (475 for circular cylinders) eddies are shed continuously from each side of the body, forming rows of vortices in its wake. The alternation leads to the core of a vortex in one row being opposite the point midway between two vortex cores in the other row, giving rise to the distinctive pattern shown in the picture. Ultimately, the energy of the vortices is consumed by viscosity as they move further down stream, and the regular pattern disappears. When a single vortex is shed, an asymmetrical flow pattern forms around the body and changes the pressure distribution. This means that the alternate shedding of vortices can create periodic lateral (sideways) forces on the body in question, causing it to vibrate. If the vortex shedding frequency is similar to the natural frequency of a body or structure, it causes resonance. It is this forced vibration that, at the correct frequency, causes suspended telephone or power lines to "sing" and the antenna on a car to vibrate more strongly at certain speeds. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Kármán vortex street」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.