大氣與森林之間紊流流場之風洞實驗; Wind tunnel measurements of turbulence flow between the plant canopies and atmosphere

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Title:	大氣與森林之間紊流流場之風洞實驗;Wind tunnel measurements of turbulence flow between the plant canopies and atmosphere
Authors:	方偉德;Wei-Te Fang
Contributors:	土木工程研究所
Keywords:	混和層流;風洞;森林;紊流;wind tunnel;plant canopies;turbulence flow;m
Date:	2004-06-17
Issue Date:	2009-09-18 17:16:09 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	大氣與森林之間的動量、熱量和質量（水汽、二氧化碳、氧氣、種子、花粉等）的傳輸不僅會影響到植物的生長，亦對森林區的蒸發散和地表附近的微氣候有重大的影響，為全球環境的變遷中重要的一環。本研究以風洞實驗來探討大氣與森林之間的混合層流，實驗中放置模型樹於風洞中的紊流邊界層之中，並改變樹木的疏密度和排列方式，在不同的下風距離量測平均風速和紊流參數，並在相鄰的兩點同時量測紊流流速，以瞭解紊流流場的相關性，以釐清樹木的疏密度和排列方式對森林之中的尾流及森林之上的混合層流的影響。實驗結果顯示(1)森林流場的風速剖面可由迴歸公式所表示；(2)在森林流場中動量的傳輸受到掃流(sweep)與噴流項(ejection)的控制，樹林愈密集的流況中掃流項對動量傳輸的貢獻愈大；(3)在樹頂之下(X/H < 1.2)縱向風速的偏度係數(右偏分佈)，但垂向風速的偏度係數卻小於零(左偏分佈)，這顯示樹林之中的掃流發生的機率較大。在樹頂之下(X/H < 1.2)縱向風速和垂向風速皆偏離高斯分佈，但樹林之上(X/H > 2)接近高斯分佈；(4)森林與大氣之間的傳輸率可以由垂向渦流黏滯係數(Eddy viscosity) 表示，隨高度增加而增加，當樹木愈稀疏時則愈大，為渦流的混合長度(Mixing length)，當樹林愈稀疏時，則混合長度也愈大。 The turbulence transport of momentum, heat and mass (water vapor, CO2, O2, seed and pollen) between the plant canopies and atmosphere not only affect the growth of plants, but also influence the evaporation, transpiration and micro-meteorology of forest area. This study used wind tunnel experiment to investigate the mixing layer flow above the plant canopy and wake flow in the canopy. Mean velocity profiles and turbulence parameters were measured at several down-wind distances. Based on the velocity measurements, the shear velocity, roughness length, displacement height, momentum thickness and cross-correlation function all were calculated and analyzed. The results showed that: Mean velocity profiles were related to canopy spacing and could be non-dimensionalized. The momentum transport was dominated by the sweep and ejection events above the tree top.
Appears in Collections:	[Graduate Institute of Civil Engineering] Electronic Thesis & Dissertation

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