多孔隙圓柱於明渠中之三維流場模擬

本研究使用FLUENT進行多孔隙圓柱之三維明渠流流場模擬。分別以大渦模擬（Large Eddy Simulation, LES）及標準k-ε紊流模式兩種方式，皆搭配體積分率法(Volume of Fluid, VOF）進行有自由液面之紊流模擬。觀察不同孔隙率之多孔隙圓柱於半浸沒（常水位）和浸沒條件（高水位）下，圓柱周圍之流況。並討論使用「實體外型框邊」與「數值摩損框邊」兩種不同方式設置圓柱邊界條件時對流場之影響。由模擬結果得知，不透水圓柱與低孔隙率圓柱皆存在馬蹄形渦流、上升流以及卡門渦街等現象，隨著圓柱孔隙率增加，馬蹄形渦流等流況漸漸消失。於低孔隙率時，LES之模擬結果較標準k-ε紊流模式能顯示出圓柱周遭之渦度變化，中、高孔隙率時，兩者差異甚小。比較實體外型框邊與數值摩損框邊之流場差異，實體外型框邊圓柱於柱後流速回復較快，數值摩損框邊圓柱則會產生柱後低速區過長之情況，後者會高估現場設置多排孔隙圓柱之適當間距。

關鍵字

多孔隙圓柱；數值模擬

並列摘要

The three dimensional flow field around a single porous cylinder within an open-channel flow is simulated using a FLUENT model and CFD software. Large eddy simulation (LES) and standard k-ε turbulence models, both of which use the volume of fluid (VOF) to trace the free surface, are used to generate turbulence in the simulation. The experimental data is used to verify and to calibrate parameters. A non-immersion condition and an immersion condition are respectively used to represent a general field case and a case with high flow. Cylinders with different degrees of porosity are tested. Two types of internal boundaries are used to represent the porous material, the physical structural frame and the numerical frictional frame and their deviation in the flow field is discussed. For a non-porous or slightly porous cylinder, the horse-shoe vortex, up flow and the Karman Vortex Street are all represented well by LES simulation. For a medium or highly porous cylinder, the horse-shoe vortex, up flow and the Karman Vortex Street are not significant so k-ε turbulence simulation is used to save time. For the two types of internal boundaries, flow past the physical structural frame recovers faster than that past the numerical frictional frame. Therefore, the distance between the two piles of porous cylinders must be estimated with caution if the latter method is used.

並列關鍵字

Porous cylinder ； numerical simulation ； large eddy simulation (LES) ； k-ε ； FLUENT

國際替代計量

多孔隙圓柱於明渠中之三維流場模擬

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