城市街道峡谷对称性对内部气流场的影响研究

Effects of symmetry of urban street canyons on their inner airflow fields

应用雷诺应力湍流模型,模拟了不同高度比的城市街道峡谷的气流场。结果表明:峡谷的对称性对其内部气流场有显著影响。前高后低型峡谷下部为逆时针旋涡,上部为顺时针旋涡,峡谷越深,流场发展的越充分;峡谷内部墙面存在明显的驻点。前低后高型峡谷只存在一个大的顺时针旋涡,随着峡谷的加深,内部气流速率有减小的趋势;峡谷达到一定深度后出现驻点。对称型峡谷内部形成了顺时针旋涡,强度不大;随着峡谷的加深,内部流场转为一顺一反2个旋涡的二元结构;仅当峡谷很深时才出现明显驻点。前低后高型峡谷的气流场形式更有利于污染物的迁移、扩散,在城市规划中应尽量结合主导风向设计这类建筑布局。

Based on Reynolds stress turbulence model, airflow fields within urban street canyons under different building heights were simulated. The numerical simulation results show that the symmetry of the street canyons has significant effects on inner airflow fields. There is a counter-clockwise vortex in the lower part of higher frontage and lower back canyon, and there is a clockwise vortex in the upper part. The deeper the canyon is, and the better the airflow field develops. There is an obvious stagnation point on the wall surface of canyon interior. Only one large clockwise vortex exists in the lower frontage and higher back canyon. The velocity of inner airflow decreases with the increase of canyon depth. The stagnation point will appear after the depth reaches a certain value. There will be a clockwise vortex in the interior of symmetric street canyon with the smaller intensity. The interior airflow field is transferred duality structure of one clockwise vortex and one counterclockwise vortex with the increase of canyon depth. When the canyon is very deep, the obvious stagnation point will appear in the symmetric street canyon. The airflow field of lower frontage and higher back canyon is advantageous to the translocation and diffusion of pollutants. Thus, this kind of building distributions should be designed in urban planning according to the leading wind direction.