不對稱街谷與喬木配置對行人風場舒適度影響之研究

Abstract

由於土地有限且快速發展，都市區域的建築逐漸趨向高密度與垂直化。然而，都市發展速度不一，導致舊建築與新高樓並存，形成複雜的都市風環境，使風環境成為都市發展的重要議題。在都市區域中，特別關注小尺度(micro-scale)的氣候環境，而在此尺度下，都市冠層(urban canopy layer, UCL)對人類生活有最直接的影響，其表面組成受到建築密度、高度、街道寬度與走向，甚至植栽配置的影響。不當的配置可能導致通風不良、部分區域出現強風的狀態，降低行人舒適度。 因應環境變遷，街道綠化已成為調節都市微氣候、提升城市美感與生活舒適度的重要策略。然而，現行法規雖已對都市建築之風環境設計提出一定規範，在街道綠化配置方面仍缺乏明確指導原則；若配置不當，不僅無助於改善街道通風，反而可能降低行人層風場的舒適性。過去研究多各別探討街谷(street canyon)尺寸、建築排列以及植栽配置，但較少全面考慮不對稱街谷(asymmetric street canyon)中喬木配置對行人層風舒適度的影響。 本研究以計算流體力學(computational fluid dynamics, CFD)數值模擬方法作為研究工具。本研究設定三項變項，分別為兩種不對稱街谷（升階街谷與降階街谷）、兩種入風風速條件，以及六種喬木組合配置方案，評估其對行人層舒適風速面積之影響。研究結果顯示：(1) 升階街谷(step-up canyon)在低風速條件下具有較高的舒適風速面積佔比，而降階街谷(step-down canyon)則相反，在高風速條件下具有較高的舒適風速面積佔比；(2) 針對不同喬木高度分析方面，在低風速條件下，無論升階或降階街谷，喬木高度對舒適風速面積的提升效果皆有限；但在高風速條件下，升階街谷以全小喬木配置(G111)、降階街谷則以全中喬木配置(G222)能提高舒適面積佔比；(3)在喬木配置位置方面，在低風速條件下，升階與降階街谷皆以中央配置中喬木、其餘為小喬木(G121)方案具有較高的舒適風速面積；在高風速條件下，升階街谷仍以(G121)舒適佔比較高，而降階街谷則以背風面配置中喬木、其餘位置小喬木(G112)具有較高的舒適風速面積。

Due to limited land availability and rapid urban development, urban areas have increasingly shifted toward high-density and vertical construction. However, the pace of development varies across different districts, resulting in the coexistence of old buildings and new high-rises. This has created a complex urban wind environment, making wind conditions a critical issue in urban development. In particular, attention is focused on the micro-scale climate environment in urban areas. At this scale, the Urban Canopy Layer (UCL) has the most direct influence on human activities. Its surface structure is affected by factors such as building density, height, street width and orientation, and even vegetation configuration. Improper arrangements may lead to poor ventilation or localized strong winds, thereby reducing pedestrian-level wind comfort. In response to climate change, street greening has become an important strategy for regulating the urban microclimate, enhancing city aesthetics, and improving wind comfort in outdoor spaces. Although current regulations provide certain guidelines for wind environment design in building development, there is still a lack of clear principles for vegetation configuration along streets. If poorly implemented, such configurations may not only fail to improve airflow but may also reduce wind comfort at the pedestrian level. While previous studies have individually investigated factors such as street canyon dimensions, building arrangements, and tree planting schemes, relatively few have comprehensively examined how tree configuration in asymmetric street canyons affects wind comfort at the pedestrian level. This study adopts Computational Fluid Dynamics (CFD) simulation as the primary analytical method. Three independent variables were defined: two types of asymmetric street canyons—step-up canyons and step-down canyons; two inflow wind speed conditions; and six tree configuration schemes. The study evaluates the effects of these variables on the area of comfortable wind speed at pedestrian height. The results indicate the following: (1) Under low wind speed conditions, step-up canyons exhibit a higher proportion of comfortable wind speed area, while step-down canyons perform better under high wind speed conditions. (2) Regarding tree height configuration, under low wind conditions, the effect of tree height on wind comfort is limited for both canyon types. However, under high wind conditions, step-up canyons perform better with a configuration of all small trees (G111), while step-down canyons show improved wind comfort with all medium trees (G222). (3) For tree placement configurations, under low wind conditions, both canyon types exhibit higher wind comfort when medium trees are planted at the center and small trees on both sides (G121). Under high wind conditions, step-up canyons still perform better with the G121 configuration, while step-down canyons achieve better wind comfort with medium trees on the leeward side and small trees elsewhere (G112).