一渠道內以低雷諾數流場流過突起物之數值研究

On the numerical study of low Reynolds number flows past a hump in a channel

潘宜婷(Pan Yi-Ting)

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(2014年)

https://doi.org/10.6837/NCNU.2014.00177

摘要

本文以一渠道內低雷諾數流場流過突起物之數值研究。以卡氏網格法解答流場過程，是結合有效的內嵌邊界法及兩步驟分步法，來採納模擬流場。突起物邊界形狀的h及a範圍選擇為y = h exp(-a2 x2)，其中h為突起物高度；a為寬度參數。研究流場模式的參數空間選擇為Re_H≤1000(H=10為渠道高度是無因次的)， h≤6.0及1≤a≤3，從數值結果得知，顯示各種變化流場模式，其中包括流場穩定、週期性的及弱混亂流。統整分析的影響，包括突起物、突起物高度在不同的流場所引起之阻力和升力。透過數值結果，得知雷諾數轉變路線由穩定到週期性再到混亂，以突起物h=4及a=1作為舉例研究，將調整Re增加及減少來計算分析，便可了解整個轉變過程。然而，經過統整分析對流場的影響，包括雷諾數及突起物高度在不同的流場所引起之阻力和升力。流場的分歧現象中獲得從穩定至週期性再到混亂路線之流場轉變。

關鍵字

穩定流 ； 期性流 ； 混亂流

並列摘要

In this study, low Reynolds number (Re) flows past a hump in a channel are numerically investigated, and a variety of distinct flow patterns are addressed. A Cartesian-grid formulation, in combination with an effective immersed boundary method and a two-step fractional-step procedure, has been adopted to simulate the flows. Boundary shape of humps were chosen to be y = h exp(-a2 x2) for a range of h and a, where h is the height of the hump and a is the width parameter. From the global point of view, there appear variety of flow patterns within the investigated parameter space, Re_H≤1000(H being the height of channel and H=10 dimensionless), h≤6.0, and , which include, steady, periodic, and weakly-chaotic flows. We numerically present these flows by tuning both Re and h quasi-stationary, and provide a broader understanding of the entire transition process. A comprehensive analysis of effects of Reynolds number, and the hump height on different flow-induced forces (drag and lift) on the hump is included in this regard. Bifurcation diagrams of the flow are obtained, which include transition from steady to periodic flows and route to chaos of the flow.

並列關鍵字

Steady flow ； Periodic flow ； Weakly-chaotic flow

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