建築物群排列方式對街谷環境風場與懸浮微粒傳輸之影響研究

Numerical Evaluation of the Effect of Building Layout on Turbulent Flow Field and Particulate Matter Transport in Street Canopies

黃為華(Wei-Hua Huang)

指導教授 ： 張倉榮

國立臺灣大學/生物資源暨農學院/生物環境系統工程學研究所/碩士(2005年)

https://doi.org/10.6342/NTU.2005.10187

摘要

本研究之主要目的為建立不同粒徑之懸浮微粒軌跡追蹤模擬方法，比較開放式 (opened) 及交錯式 (staggered) 等兩種建築物群排列方式之三維度環境風場及懸浮微粒之傳輸行為與排除效率。本研究對三維度建築物群之環境風場數值分析，係採用有限體積法(finite volume method) 離散控制方程式，以SIMPLE法耦合速度及壓力，使得整個流場符合質量守恆及動量守恆，同時結合大渦模擬 (large eddy simulation，LES) 紊流模式、亞格點尺度應力模式 (subgrid scale stress model，SGS) 與邊牆函數 (wall function) 來模擬紊流流場。本研究並以拉格蘭日 (Lagrangian) 觀點之氣懸微粒軌跡追蹤模式模擬建築物群之懸浮微粒軌跡傳輸行為。微粒軌跡追蹤模式除了計算傳統的阻力與重力外，又增加考慮Saffman升力與布朗運動作用力對於微粒的影響。本研究首先進行微粒釋放粒數之敏感度分析，結果當微粒釋放總粒數超過1萬顆以上時，可確保氣懸微粒質量濃度與粒數濃度之精確度。
在比較開放式街谷與交錯式街谷的行人風場後，結果指出在開放式建築物群中微粒懸浮於直流區之PM10濃度高於尾流區約10％，且PM10之微粒排除效率亦比PM1及PM2.5較為不佳。在交錯式建築物群中微粒懸浮於直流區則較尾流區高出約70％。在微粒排除效率方面，PM10在兩種建築物排列方式中都較PM2.5及PM1佳，交錯式又較開放式顯著。
在微粒傳輸過程中由於大微粒具有較大的慣性衝擊與重力沈降能力，當大微粒傳輸至建築物後方時，較易離開因建築物排列方式所造成的渦流，小微粒因放鬆時間小比大微粒需要更久的時間沉降於地面且會在隨著次要氣流或是環境流場所產生的漩渦等影響來回地盤旋而滯留於尾流區，故造成交錯式建築物群的尾流區內PM2.5及PM1的微粒質量濃度累積最甚。

關鍵字

計算流體力學 ； 都會建築物群街谷 ； 有限體積法 ； 大渦模擬紊流模式 ； 微粒軌跡追蹤 ； 微粒排除效率。

並列摘要

The main objectives of this study are to establish trajectory tracking technique for different particle sizes and to compare the effects of different building layout (i.e., opened and staggered street canopies) on turbulent flow field and particulate matter transport in urban street canopies.
To simulate the three-dimensional turbulent flow field under different urban street canopies, we select the finite volume method to discretize the governing equations of our numerical model. SIMPLE scheme is used to adjust flow field to satisfy the continuity equation. Large eddy simulation (LES) together with the subgrid-scale stress model (SGS) and the wall function are adopted to model the turbulence flow field in the study. The Lagrangian particle trajectory tracking technique is adopted to investigate particulate matter transport behavior in urban street canopies. The effects of the drag force, gravitational force, Brownian motion, and Saffman lift force on particles are all considered in the particle tracking technique. A sensitive analysis is firstly conducted to assess how many particles are necessary to be released in the simulated 3-D turbulent flow field for maintaining in a stable concentration profile. The analysis indicates that as the released particles are more than 10000, the particle and number concentration distributions approach to a steady profile.
The simulated results show that, in the opened street canopy at the pedestrian wind airflow range, PM10 concentration in the gap area is 10% higher than that in the wake zone. However, it increases to 70% in the staggered street canopies. Also, in the gap area, the removal efficiency for PM2.5 and PM1 is better than that for PM10, especially in the staggered street canopies.
The larger particles are easier to deposit than smaller ones. Once the large particles are transported to the vortex region behind the buildings, it is hard for them to escape from the region. The smaller particles need longer time to deposit. In the staggered street canopies, these small particles would follow low-velocity airflow and wander in the wake zone. This phenomenon results in accumulations of PM2.5 and PM1 in this region.

並列關鍵字

Computational fluid dynamics ； Urban street canyon ； Finite volume method ； Large eddy simulation ； Particle trajectory ； Particle removal efficiency

參考文獻

32.謝怡芳，2004，「三維度紊流大渦模擬在多區間建築物室內環境風場之應用研究」，國立台灣大學生物環境系統工程學研究所碩士論文。

33.高宏名，2004，「以三維度微粒軌跡追蹤模式研析多區間建築物室內懸浮微粒傳輸行為」，國立台灣大學生物環境系統工程學研究所碩士論文。

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