A Model for Predicting Vortex Motion in a Viscous Wake

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Title:	A Model for Predicting Vortex Motion in a Viscous Wake
Other Titles:	粘性尾流之渦流運動預測模式
Authors:	Tseng, Cheng-Yuan
Contributors:	淡江大學水資源及環境工程學系
Date:	1988-04
Issue Date:	2010-03-26 16:28:51 (UTC+8)
Publisher:	臺北市：中國農業工程學會
Abstract:	尾流(Wake)形成之主要機構原理尚未被透徹了解，旋渦(Vortex)受粘性(V iscosity)之影響其流函(Stream function)尚無解析解，因此粘性尾流(Viscous wake)仍是現代流體專家探討專題之一，本文主要構建粘性尾流之渦流運動(Vortex motion)預測模式，其輸入資料僅需圓柱直徑、雷諾數(Reynolds number 及史戳荷數(Strouhal number)，結果顯示第一個旋渦之核心半徑幾近於水流於圓柱分離點之邊界層厚度，而與1986年Wei與Smith之假說相映。實驗亦證實粘性尾流中之旋渦係由四個在分離線(Separation line)形成之副旋渦(Secondary vortex)配對結合而成，首度使尾流形成主因有合理性解釋是為本文之貢獻。依時間之變化本模式可測單一旋渦之核心半徑及速度剖面，亦可推測第n個旋渦弘度與極大速度。在應用方面，易於以線性疊加(Super position)計算粘性尾流中無限多旋渦之速度場。經與理想流之速度場比較，顯示粘性之影響使旋渦核心之速度由理想尾流(Potential wake)之無限大改變為趨近於零較符實際現象。本研究之初步成果顯著，尚待繼續。The results of the model has shown that the radius of the first shed vortex core is nearly equal to the boundary layer thickness at the separation point of the cylinder. Research at Albrook Hydraulic Laboratory has shown that the initiation of Strouhal vortex is due to the pairing of four secondary vortexes. A numerical model predicting the maximum velocity, core radius, tangential velocity profile, and strength of the nth vortex behind a circular cylinder has been developed. As input, this model requires the characteristics of the viscous wake as well as the Strouhal and Reynolds numbers associated with the flow around the cylinder. By superposing the velocity components of infinite vortexes in the wake, the velocity field has been analyzed. Comparison of the velocity field for both viscous and potential wakes are good, with some variance existing in the velocity distribution in the viscous core.
Relation:	農業工程學報 34(3)，頁18-32
Appears in Collections:	[Graduate Institute & Department of Water Resources and Environmental Engineering] Journal Article

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