浸沒與非浸沒透水性圓柱之受力及流場模擬研析

Abstract

本研究以三維數值模式模擬水流流經透水性圓柱之流場，探討透水性圓柱於不同浸沒水深的流場特性及受力情形。模式中使用有限體積法離散控制方程式，並以標準k-ε紊流模式及體積分率法，模擬紊流流況及自由液面之變化情形。為了呈現水流受透水性圓柱之阻滯現象，孔隙介質流模式將引用於模擬當中。與水工模型試驗驗證後，發現模式與試驗結果有一致的趨勢，顯示本研究所選用的模式應用於研究流場具有足夠的精確度。 在單根透水性圓柱應用案例中，流況分為浸沒及非浸沒等五組不同平均水位，且採用五種不同孔隙率。非浸沒流況下，圓柱受力與平均水位成正比關係；浸沒流況下，圓柱受力則與平均水位為反比關係。另外，平均水位在略等同於圓柱高度時，圓柱受力為五組不同平均水位中最大。在多排圓柱群應用案例中，一共設置四種模擬情境。案例A：非交錯排列之透水性圓柱群於浸沒流況、B：非交錯排列之實心圓柱群於浸沒流況、C：交錯排列之透水性圓柱群於浸沒流況、與D：非交錯排列之透水性圓柱群於非浸沒流況。在案例A和B中比較透水與實心圓柱群排與排間的受力差異，受力折減率各別為17%與11%，顯示透水性圓柱群中排與排間的影響較大。在案例A和C中，受力折減率在交錯排列下為25%，其較非交錯排列下之17%高。在案例A和D中，受力折減率在非浸沒流況為27%，而在浸沒流況為17%。

In this study, flows through porous cylinders are simulated by three-dimensional computational fluid dynamics software FLUENT and their acting forces in different water depths are discussed. The standard k-ε turbulent model and the volume fluid method (VOF) are adopted to describe the turbulent flows with free surface. To reflect the blockage effect of flows through porous cylinders, a porous media theory is introduced herein. The simulated results against the experimental data show good agreement. The resistant forces on a single cylinder with various porosities in various water depths are investigated. It is found that the resistant force increases as the water depth increases in non-submerged flows while the resistant force decreases as the water depth increases in submerged flows. In the cases of multi-row cylinders, four scenarios such as Scenario A: non-staggered porous cylinders in submerged flows, Scenario B: non-staggered solid cylinders in submerged flows, Scenario C: staggered porous cylinders in submerged flows and Scenario D: non-staggered porous cylinders in non-submerged flows are performed. To summary, from Scenarios A and B, the reduction rates in average force are respectively 17% and 11% for porous and solid cylinders. It means that the interacting effect between two rows of porous cylinders is more significant. To compare Scenarios A and C, the reduction rate in average force as 25% in staggered arrangements is larger than that as 17% in non-staggered arrangements. It can be found that the reduction rate in average force is 27% in non-submerged flows while that is 17% in submerged flows in Scenarios A and D.