Abstract: The concept of leaf area index(LAI) is introduced into a urban street layer(USL) model to simulate the windbreak effects of a small-sized green belt on the wind environment in USL. Comparison between simulated results and the field observations shows that the model can be reasonably used to simulate the dynamical sheltering effects of the windbreak. In the research the model is used to study the wind environment in the vicinity of a tall building affected by a small-sized green belt. The numerical experiments show that the green belts exert significant effects on the pedestrian level wind field caused by tall buildings and a well-designed small-sized green belt may well improve the wind environment in the vicinity of the tall buildings. In addition, it is also found that without the green belt wind speeds in the corner flow region at the lateral sides of the building may reach 5m/s with the inflow wind speed of 3m/s，while with a properly designed green belt the corner flow speeds in the same region may decrease to 3.5m/s.

Key words: urban wind environment, green belt, leaf area index(LAI), numerical simulation

摘要： 在城市街谷模式的基础上引入叶面指数，对小型林带的防风效应进行模拟、检验，通过实验结果与野外观测值的比较, 证明此模式能较为合理的模拟防护林的动力遮蔽效应；将此模式应用于小型绿化带对高大建筑物周围风环境的影响的数值模拟，数值实验证明在城市冠层内，城市小型绿化带对高大建筑物周围行人高度的风场环境影响显著，设置合理的小型绿化带对城市高大建筑物附近风场有良好的改善效果。模拟实验中可见，在3m/s的入流风速下，建筑物侧面的角隅流达5m/s，设置合理的绿化带可使之降低到3.5m/s。

关键词: 城市风环境, 绿化带, 叶面指数, 数值模拟