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A Study on the Shelter Effect of Windbreak Fence with Tilted Vanes
|關鍵字:||防風柵;windbreak fence;防風效果;傾角式防風柵;現地試驗;風洞試驗;數值模擬;空氣動力學;shelter effect;windbreak with tilted vanes;field experiment;wind tunnel experiment;numerical simulation experiment;aerodynamics||出版社:||水土保持學系||摘要:||
台灣沿海地區終年為風害侵襲，往昔防風措施常採用防風牆、防風網及防風柵等構造物，以達到削減風力之目的，然各種構造物有其優點亦有缺點。當防風構造物本身完全不透風時，氣流必須越過構造物，在背風面短距離範圍內即迴流於地表，使得防風效果不佳；又防風構造物若部份透風時雖可減小迴流，但阻風率過小時，氣流大部份直接穿過構造物，無法有效降低風速。本研究為解決此一問題，乃針對可調節柵板傾角之防風柵，依柵板傾斜角度為0 o、15 o、30 o、45 o、60 o、75 o和90o等條件進行試驗，探討該傾斜柵板對消減氣流能量、減低風速，為增加防風效果之效應。
Wind damage encroached upon Taiwan coastal area throughout the years. Windbreak walls, nets, and fences were the windbreak constructions that adopted frequently to attain the object of cutting down wind velocity in the past. However these constructions possess their advantages and shortcomings. When windbreak structure was entirely stuffy, the airflow necessarily went over it. The backward current would flow toward to earth''s surface in a short distance behind the lee side to cause poor shelter effect. Meanwhile windbreak is partial penetrated, backward current will let up, and the most airflow will thread windbreak through directly therefor the purpose of this study is to investigate these phenomena, to experiment the fence with the tilted vanes making trial of 0, 15, 30, 45, 60, 75, 90 angles. And to analyze the effect of decreasing air-flow energy , blocking wind velocity and improving shelter effect for these tilted vanes of fence.
Filed study, wind tunnel experiment, and numerical simulation are three different methods to explore the shelter effect of fence with tilted vanes. In the field the fence was practically mounted in open area of in No. 6 Naphtha Cracking Industry Area of Mailiao and to estimate wind velocity and observe smoke distribution in the site. The study was to analyze the characteristics of vanes angle, blockage ratio ( blockage area/ fence complete area ), width ( vanes width ), multi-angle ( combinations of semi-fence in different angle ) characteristics of fence not only in field but also in 1/30 model scale of wind tunnel. All the study of blockage ratio, angle, multi-angle, and precise angle (minimum angle 2.5) are consequently characterized in finite difference method of large-eddy numerical simulation study.
Tilted 75o vanes result the best shelter effect. The effect decreased as tilted angle more or less than 75 o. Raising height of air flowing through fence was higher along as large tilted angle. The flow field was approximately similar to blank test in small tilted angle. The shelter effect of multi-angle tests, and H vanes width presented better shelter effect in the result of wind tunnel experiment. Tilted 62.5o vanes revealed the best shelter effect in numerical simulation. Although the disparity of Windbreak Index value due to the difference of velocity inflow profile in three methods of experiments, the characteristics of flow field and tendency of shelter effect are significantly consistent in the results.
Finally, the fences with tilted vanes are highly usability for the coastal area in future and promote 9% shelter effect to stuffy wall and 15% to blockage-50% fence, also improve the shelter effect from disadvantages of strong backward current and lower blockage of windbreak constructions.
|Appears in Collections:||水土保持學系|
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