流過橢圓柱體流場渦旋逸出啟動之數值研究

Onset of Vortex Shedding in Flows Past an Elliptic Cylinder

楊斯容(Sz-Rung Yang)

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(2011年)

摘要

本文由巢狀網格來達到局部網格加密的效果。對不穩定、具黏滯性且不可壓縮流流場，為求解複雜邊界，採用沈浸邊界法配合巢狀網格進行數值模擬。欲求解巢狀網格的問題主要在對巢狀網格邊界加密及對控制方程式離散的精確性是重要的，而粗細網格交接面可當作網格控制面。在程序解答的準確性上去修改離散式即可以有計畫有步驟的發展，因此，本文闡述了發展高效率和高精準度的巢狀網格。藉由巢狀網格方法測試流過對稱地置放於渠道內，不同長短軸比之橢圓形柱體障礙物流場，得出平均昇力阻力係數、渦漩逸出的變化，進而準確預測發生渦漩逸出之臨界雷諾數，模擬所求之臨界雷諾數也確實呈現遞增狀態，證實網格局部加密部份重疊的正確性，同時得出該測試方法適用之橢圓形柱體長短軸比。並從上述之數值試驗，確認巢狀網格法可以有效率來獲得數值結果。

關鍵字

巢狀卡氏網格 ； 數值方法 ； 沈浸邊界法

並列摘要

In this paper, the local grid refinement is focused by using a nested grid technique. The nested Cartesian grid method is developed for simulating unsteady, viscous, incompressible flows with complex immersed boundaries. The key aspects that need to be considered in developing such a nested grid solver are imposition of interface conditions on the nested-block boundaries and accurate discretization of the governing equation in cells that are with block-interface as a control surface. A new interpolation procedure is presented which allows systematic development of a spatial discretization scheme that preserves the spatial accuracy of the underlying solver. As a result, high efficiency and accuracy nested grid method is developed. This paper describes the development of high efficiency and high precision of the nested grid. By nested grid method to test flowchannels symmetrically placed in the inside,a different length than the oval-shaped cylinder axis obstacles logistics field, arrive at the average lift drag coefficient, vortex escape change, and thus to predict occurrence of vortex vortex escape the criticalReynolds number, find the critical Reynolds number simulation indeed showed increasing state, local refinement grid confirmedthe correctness of some overlap, and arrive at the test method applies to the length axis of the elliptical cylinder than.And from theabove numerical experiments confirm the nested grid method can be efficient to obtain numerical results.

並列關鍵字

nested Cartesian grid ； numerical method ； immersed boundary method

參考文獻

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