THE EFFECTS OF GREEN VEGETATION BELT HEIGHTS ON THE WIND FLOW AND TRAFFIC EMISSION DISPERSION AROUND ROADSIDE BUILDING-A WIND TUNNEL STUDY

綠帶植生高度與道路旁建築物對於風場與交通廢氣排放擴散之影響效應－風洞實驗研究

10.6652/JoCICHE.202309_35(5).0005

Bao-Shi Shiau(蕭葆羲)；Hsiao-Peng Huang(黃小芃)；Xuan-Han Lu(呂宣翰)

wind tunnel ； traffic emission ； turbulent boundary layer flow ； laser light sheet ； smoke visualization ； cavity flow ； green vegetation belt ； leaf area index ； line source ； pollutant dispersion ； 風洞 ； 交通廢氣排放 ； 紊流邊界層流 ； 雷射光頁 ； 煙流示現 ； 穴流 ； 綠帶植生 ； 葉面積指標 ； 線源 ； 污染擴散

中國土木水利工程學刊

35卷5期（2023 / 09 / 01）

483 - 489

英文;繁體中文

The green vegetation belt has been shown reductive effects on air-borne pollutants concentrations, therefore is usually designed to use as improving the local air quality in roadside buildings. In the present study, wind tunnel model experiments were performed to investigate the flow and traffic emission of air borne pollutants dispersion around roadside building with different heights of green vegetation belts under a turbulent boundary layer flow. Flow measurements of the canopy of green vegetation belt and roadside buildings incorporated with smoke flow visualization by laser light sheet were made. Methane mixing with pure air was adopted to simulate the air borne pollutant. Line source was employed to simulate the road traffic emission. The sampled tracer was analyzed by the flame ionization detector (FID) to yield the mean concentration. The leaf area density (LAD) of green vegetation belt model was 2m^2m^(-3) which expressed the sparse trees with leaf area index LAI = 1.565. Measured wind speed profile shows that wind speed changes significantly with increasing the green vegetation belt height. The distribution of the concentration is strongly affected by the cavity flow in the region between the green vegetation belt and building. The higher the green vegetation belt, the induced updraft motion became more significant. The updraft motion lofts the traffic emission plume. Concentration distribution measurements exhibited the vertical dispersion parameter (dispersion length scale) of each downwind distance of source decreased as the height of green vegetation belt increased in the region between green vegetation belt and building. As increasing the height of green vegetation belt leads to lower the vertical location of centroid of pollution cloud due to pollution accumulation. When the green vegetation height increased from 0.3 W to 0.9 W (W: building width), the dispersion parameter (dispersion length scale) decreased about 40% to 50% in the region between green vegetation and building.

道路植樹形成綠帶，可有效阻隔道路交通廢氣，有利於改善路旁建築周遭之空氣品質。本文應用風洞實驗探討分析在中性大氣紊流邊界層流橫風作用下，道路綠帶植生高度與路旁建築物對於環境風場與交通排放廢氣擴散之影響效應。綠帶植生採用葉面積密度LAD = 2m^2m^(-3)（相當於較稀疏之樹葉植生），換算葉面積指標為LAI = 1.565。交通廢氣污染排放採用線源排放模擬。風場量測平均風速並配合煙流視現觀察流場回流區。濃度採用甲烷為追蹤劑，以氣袋採集後，使用火焰離子偵測器分析採樣之濃度。實驗研究結果顯示：（1）綠帶植生高度增加時，因綠帶與道路旁建築物阻擋效應，二者間區域之風場明顯呈現穴流現象，且穴流區頂部氣流出現抬升情況，造成部分廢氣污染上飄。（2）綠帶植生高度增加時，綠帶與道路旁建築物二者間區域之廢氣污染因穴流造成濃度累積，使得在穴流區之污染團質心高度下降。（3）綠帶植生高度從0.3 w增加至0.9 w時（w為建築物深度），在綠帶植生與道路旁建築物二者間穴流區內各下游斷面廢氣污染團之垂直擴散尺度減小約40%至50%。

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