流過兩個具相對攻角橢圓流場之數值研究

Numerical Study on the Flow Past Two Elliptic Cylinders With Different Attack Angles

張齡勻(Ling-Yun Chang)

指導教授 ： 彭逸凡

國立暨南國際大學/科技學院/土木工程學系/碩士(2010年)

摘要

本文使用卡式座標(Cartesian Grid Method)研究流過兩個具相對攻角橢圓柱之流場。流場藉由Navier-Stoke方程及連續方程求解，計算過程採用分步法 (Fractional Step Method) 。以卡式網格解答流場過程中，含複雜邊界之橢圓障礙物則以 Ravoux 等人 [1] 發展的內嵌法 (Embedding Method)，局部網格加密則用巢狀網格(Nested Cartesian Grid Method)處理之。本文分析兩橢圓柱不同幾何配置及不同入流條件對橢圓柱流場的影響。文中使用參數為橢圓長短軸比 (2:1及3:1)、雷諾數 ( 及 )、兩橢圓圓心間距G(Gap=1.6~6.0)、雙橢圓間夾角 ( =4 ~ -40 )。本文探討流過兩個具相對攻角橢圓柱流場共有29組計算例中，可歸納三種流場型態第一種為異相位O(Out of phase) 共15組、第二種為同相位I (In-phase) 共3組、第三種為非對稱渦漩A (Asymmetry) 共11組。

關鍵字

橢圓柱 ； 渦漩逸出 ； 內嵌法 ； 巢狀網格

並列摘要

Article, Cartesian Grid Method is adopted to investigate Flow Past Two Elliptic Cylinders With Different Attack Angles. In solving the Navier-Stokes and continuity equations, a finite volume method is used in conjunction with a two-step fractional-step procedure. The key aspect in developing a Cartesian grid method for flow with complex geometries is imposition of bluff bodies. In this study, a simple concept of Immersed Boundary method is adopted by using distributed body forces in the Navier-Stokes equations instead of the existence of bluff solid bodies. Similar procession has been applied by Ravoux et al. [1] and they referred it as Embedding method. The local grid refinement is also used in this study by applying the nested grid technique.
Article, flows past two elliptic cylinders with different attack angles are studied systematically. Flows at different Reynolds numbers with Re=200 and Re=300, different ellipse aspect ratio with aspect ratio=2 and aspect ratio=3, various gape ratio of G=1.6~6.0, and various attack angles of =40 ~ -40 are computed and observed.
Article, 29 flows past two elliptic cylinders are studied and 3 different kind of flow patterns are founded. They are In-phase flow, Out of phase flow, and Asymmetry flows, respectively.

並列關鍵字

elliptic cylinders ； Vortex shedding ； Embedding Method ； Nested Cartesian

參考文獻

1.Ravoux, J.F., Nadim, A., and Haj-Hariri, H., “An Embedding Method for Bluff Body Flows: Interactions of Two Side-by-Side Cylinder Wakes,” Theoretical and Computational Fluid Dynamics, Vol. 16, pp. 433–466 (2003).

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