斜風影響防風網防風效果之探討

The Protective Efficiency of Windbreak Net by the Influence of Oblique Wind

江永哲(Yung-Cheh Chiang) ； 王冬成(Tong-Cherng Wang)

《中華水土保持學報》 26卷1期 (1995/03) Pp. 17-29

https://doi.org/10.29417/JCSWC.199503_26(1).0002

摘要

往昔本省沿海防風林營造或防風網之設置，大多以垂直東北風向為準則，而忽略東西走向之海岸地形受斜風的影響，因此，不但無法有效防風防鹽，反而易形成風口，加速風砂及飄鹽之危害，本文之研究目的，乃針對此問題，探討斜風對防風網之影響，藉由野外實測結果瞭解斜風與防風網防風功效之關係，並以室內風洞試驗加強分析探討，以為佐證。茲就試驗分析結果摘要如下：(1) 氣流受防風網阻截，於背風面之風速剖面不符對數法則，此現象隨入射角之增大而趨緩，而隨背風面距離之增加而逐漸依復對數分布。(2) 水平風速分布隨入射角增大，風速恢復愈快，保護距離及保護指數隨之降低，防風效果愈差。(3) 受氣流導向之影響，防風網前翼測線隨入射角之增大，其防風功效愈低，後翼測線則反之。(4) 保護距離與保護指數皆與cos α（α: 入射角）成直線正相關，亦即二者皆與入射角α存在一餘弦函數之關係。(5) 在高密度情況下，防風網隨入射角之增大所造成之密度效應，在防風功效上遠不及入射角α之影響。

關鍵字

斜風 ； 防風網

並列摘要

In the past, the afforestation of the windbreak or arrangements of the windbreak net along the coast of Taiwan, often ignore the fact that the east-west coastal topography of Taiwan is also influenced by the oblique wind in addition to the north-eastern monsoon. With field observation and the indoor wind tunnel experiment this study aims at discussing the relationship between the ablique wind and the wind reduction efficiency of the windbreak net. The results are summarized as follows: (1) Due to the obstruction of the windbreak net, the profile of vertical wind velocity at the leeward does not correspond to the logarithm law. But with the increase of the incidence angle and distance, it will restore back to follow logarithm distribution gradually. (2) The horizontal distribution of the wind velocity increases with the increasing incidence angle. However, with the increase of the incidence angle, the protected distance and the protected index as well as the wind reduction efficiency of the windbreak net decrease. (3) Due to the influence of the air flow dirction, the wind reduction efficiency of the forward-wing measure line decreases with the increaseing incidence angle. On the contrary, with the increase of the incidence angle, the wind reduction efficiency of the backward-wing measure line increases. (4) Both the protected distance and the protected inder have a linear relationship with cos α, In other words, there is a cosine function relationship between the protected distance, the portected index, and the incidence angle α. (5) When the density of the windbreak net is high, the incidence angle α has greater influence on the wind reduction efficiency than the density effect caused by the increase of the incidence angle.

並列關鍵字

Oblique Wind ； Windbreak Net