Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/33497
標題: Studies on the Shelter Effects of Non-Penetrable Windbreak Structures
不透風式構造物之防風功效研究
作者: Huang, Long-Ming
黃隆明
關鍵字: 不透風式;Non-Penetrable;防風構造物;煙線;迴流區;分離流線;數值模擬;Windbreak Structures;Streak Line;Reverse-Flow Area;Separation Line;Numerical Simulation
出版社: 水土保持學類
摘要: 
The purpose of this study is to examine the shelter
effects of non-penetrable windbreak structures. The field
experimentation was carried out at two appropriately selected
windbreak embankments in Chih-Kan, Peng-Hu Island and Lu-Kang,
Chang-Hwa County. In addition to the velocity measurements,the
velocity field behind the structure was assessed to determine
the shelter effect of the windbreak em- bankment.The actual
current flowing through the windbreak embankment is examined
with the smoke experiment. In order to compensate the
deficiency from the field experiment, this study employed 30
scaled models for wind tunnel experiments. Beside visualization
analyses on the general relative wind velocity and flow field,
the impact of drag coefficient and pressure distribution to
the structure''s shelter effects is explored. To further
supplement the singular tests of field experiments and wind
tunnel experiments,sixteen cases of study are selected to
supply more complete flow field and the structure''s sustaining
conditions. The results are summarized as follows: 1. Five
best multiple regression equations relating the shelter area
to the structure''s geometric shapes and a best multiple regres-
sion equation relating the drag coefficient to the structure''s
geo- metric shape are proposed based on Buckingham Pi theorem
and a step- wise multiple regression analysis. These equations
can be utilized as the important guidelines for the designs of
non-penetrable wind- break structures. 2. Through comparisons
on the vertical velocity profiles, the drag coefficient,the
streak line pattern and the results of the numerical
calculations, the shelter effects of non-penetrable windbreak
struc- tures are described as follows: a) The windward
inclined angle effect When the height,the top thickness and
the leeward inclined angle are the same, a greater windward
inclined angle gives bigger average wind pressure on the
surface. Therefore, the weaker the average flow speed along
the upward slope, the stronger the vertex part of the
horizontal wind velocity near the separating point of the
windward surface; thus the bigger the airflow inertia. This
results in more significant upward airflow variation,and more
gradual downward move- ment of separation line. This is
beneficial to the expansion of re- verse-flow area above the
leeward surface, and it also increases the shelter efficiency.
As a result, the inclined angle of the windward surface is the
major factor determination to influence the strength of flow
near the separation point. In general, a greater windward
inclined angle leads to stronger separating point strength, a
stron- ger the airflow inertia, and a larger reverse-flow
area. b) The leeward inclined angle effect When the
height, the top thickness and the windward inclined angle
are the same, a greater leeward inclined angle gives smaller
average wind pressure on the surface. Therefore, a stronger
average flow speed along the upward slope results in more
significant sepa- ration line''s ascending effect, and a slower
descend. As a result, the inclined angle of the leeward
surface is the major factor in affecting the ascend of
separation line.In general,a greater leeward inclined angle
yields weaker negative pressure on the leeward sur- face, a
stronger airflow inertia, and a larger reverse-flow area. c)
The top thickness effect When the height, the windward
inclined angle and the leeward in- clined angle remain the
same,a greater top thickness leads to stron- ger suction effect
on the surface of the vertex part, and a tendency to make the
separation line descend in advance. In addition, due to the
thickness increase on the vertex part, the abrasive effect will
increase,but the airflow inertia is weaker.Consequently the
reverse- flow area is smaller and the shelter effect will also
decrease. How- ever, in this study, the increase in the top
thickness relative to the height is less significant.
Therefore,the resulting variation in the shelter effect is less
prominent. d) The geometric shape effect Given the same
height with variation to the windward inclined angle,the
leeward inclined angle and the top thickness,the structure will
produce different profiles. This study classifies the structure
into three major categories. The results indicate that the
reverse- flow area of a flat standing structure is clearly
larger than those of the triangle and the trapezoid
structures.Among them,the reverse- flow of the trapezoid
structure has the smallest shelter efficiency. The reason for
the variation to this aforementioned mechanism is due to the
complexity of the flow. e) The inclined angle complement
effect Among the flat structures, the windward inclined
angle and the leeward inclined angle are supplementary to each
other. When the two are equal, it is an upright wall structure.
As a result, the airflow inertia is the strongest in this
instance and the shelter efficiency is optimal. When one of the
sequences reduces, the shelter effects will decrease
accordingly. 3. The numerical simulation results indicate
that under the con- sideration of the shelter area the
Renold number change has a mild effect on the shelter effect of
the structure. However, the boundary layer thickness variation
has more significant influence on the she- lter effects of the
windbreak structure.

本研究之目的係以實驗及數值方法,探討不透風式構造物之防
風功效;在現地實驗方面,於澎湖赤崁及彰化鹿港地區,勘選適宜之 防
風堤試區兩處,除進行風速觀測,藉以瞭解氣流通過防風堤之分布 以分
析防風堤之防風功效外,並配合煙霧實驗,以觀測氣流通過防風 堤之實
態;而為彌補現地實驗之不足,研究中以30組縮尺模型進行風 洞實驗,
除一般性相對風速及流場可視化之分析外,更深入探討阻力 係數與壓力
分布對構造物防風功效之影響;又為進一步彌補現地及風 洞各單項試驗
之缺憾,因而再選擇16組研究個案,從事數值模擬,期 能瞭解流場變化
對構造物防風功效之影響,藉以提供更為詳盡之流場 狀況及構造物之受
力情形,使本研究之成果更臻完整。茲將研究之重 要結果摘述如下︰
一、經由柏金漢π定理以及逐步複迴歸分析結果,獲得五組防風面積
與構造物幾何形狀間之最佳複迴歸方程式,以及一組阻力係數與 構
造物幾何形狀間之最佳複迴歸方程式,可提供從事不透風構造 物工
程規劃時之重要參考依據。 二、經由風速剖面、阻力係數、壓力係數、
煙線實驗及數值計算之相 互比較佐証,對於不透風構造物之防風機
制,可歸納獲致下列幾 項效應綜合作用之結果︰ 1.迎風面傾斜
角之效應︰當高度、頂部厚度及背風面傾斜角皆相同 時,迎風面傾
斜角愈大,則其表面所承受之平均風壓力也愈大, 因而沿斜面向上
之平均流速愈弱,則在頂部迎風面邊緣分離點處 之水平方向流速較
強,亦即氣流之慣性力較大,造成氣流向上偏 移的效應愈顯著,使
得分離流線延緩下降,而有助於背風面迴流 區之擴大,同時亦提高
其防風功效;由此得知,構造物迎風面傾 斜角是影響分離點強度之
主要因素,傾斜角愈大,分離點強度愈 強,則氣流慣性力愈大,所
形成之迴流區愈廣。 2.背風面傾斜角之效應︰當高度、頂部厚度及迎
風面傾斜角皆相同 時,背風面傾斜角愈大,則其表面所承受之平均
風壓力愈小,因 而沿斜面向上之流速愈強,造成分離流線上捧的現
象愈顯著,同 時延緩其下降,因此,有助於迴流區之擴大,同時亦
提高其防風 功效;由此得知,構造物背風面傾斜角是影響分離流線
上移之主 要因素,傾斜角愈大,背風面之逆壓愈弱,則氣流慣性力
愈大, 所形成之迴流區愈廣。 3.頂部厚度之效應︰當高度、迎
風面傾斜角及背風面傾斜角皆相同 時,頂部厚度愈厚,其頂部表面
所產生之吸附效應愈強,有促使 分離流線提前下降的趨勢;此外,
由於頂部厚度增加,摩擦效應 亦隨之增強,則氣流之慣性力較弱,
因而所形成之迴流區較小, 防風功效亦隨之降低;但因本研究中,
頂部厚度之增加量對高度 之比,並不顯著,因而此效應對防風功效
所造成之差異並不明顯 。 4.幾何形狀之效應︰當高度相同時,
隨迎風面傾斜角、背風面傾斜 角及頂部厚度之變化,構造物將產生
多種不同的斷面,在本研究 中將其歸納為三大類型,經分析結果發
現,直立平面式構造物之 迴流區明顯大於三角體及梯形體,又其中
以梯形體之迴流區最小 ,防風功效最差,造成此種差異之機制,如
上述所言,為多種因 子互動之結果。 5.傾斜角度互補之效應︰
在平面式構造物中,迎風面傾斜角與背風 面傾斜角彼此互為補角,
當二者相等時,即為直立牆構造物,由 上述得知,此時氣流之慣性
力最強,因而防風功效最佳;又當其 中之一順序遞減時,其防風功
效亦隨之遞減。 三、經由數值模擬結果証實,流場條件中,雷諾數超過
紊流領域之變 化對構造物防風功效影響極微,但邊界層厚度變化對
構造物防風 功效影響則較為顯著。
URI: http://hdl.handle.net/11455/33497
Appears in Collections:水土保持學系

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