Abstract
Trees have a significant impact on the airflow and pollutant diffusion in the street canyon and are directly related to the comfort and health of residents. In this paper, OpenFOAM is used for simulating the airflow and pollutant diffusion in the street canyon at different height–width ratios and tree layouts. Different from the drag source model in the previous numerical simulation, this study focuses on the characterization of the blocking effect of tree branches on airflow by using more precise and real tree models. It is found that the airflow is blocked by the tree branches in the canopy, resulting in slower airflow and varying velocity direction; the air flows in the pore area between trees more easily, and the vortex centers are different in cases where the street canyon shape and tree layout are different. Low-velocity airflow distributes around and between two tree canopies, especially under the influence of two trees with different spacing. At the height of the pedestrian, the tree branches change the vortex structure of airflow, and thereby high pollutant concentration distribution on both sides of the bottom of the leeward side of the street canyon changes constantly. In the street canyon, the small change in tree spacing has a very limited influence on the pollutant concentration. The street canyon has the lowest average pollutant concentration at the largest y-axis direction spacing between two trees.
Highlights
A street canyon is a typical micro-unit of urban architecture
At different locations of the computational model (x = 0.25 H, 0.5 H, 0.75 H), the numerical simulation results are in good agreement with the experimental results [31] and numerical simulation results using large eddy simulation [32], meaning that the algorithm in this paper can be used for the numerical simulation research of pollutant diffusion and airflow in the street canyon under the influence of trees
The structure of the flow field in the street canyon is affected by three factors, including street canyon morphology, number of trees in the street canyon, and tree spacing
Summary
A street canyon is a typical micro-unit of urban architecture. The air quality of street canyons deteriorates because of pollutant emissions from automobiles. Wang et al [10] proposed a coupled large-eddy simulation–Lagrangian stochastic model to study the pollutant dispersion in urban canopy layers under the influence of trees. These studies further confirm that street canyon geometry and trees jointly affect the pollutant diffusion and airflow in the street canyon. The research on pollutant diffusion in the street canyon under the influence of trees has been extended to the complicated structures of urban buildings [11], dry deposition [12], tree-planting pattern and trunk height [9], air stability [13], etc. This study reflects the influence of trees on the pollutant diffusion in the street canyon more truly and is of considerable significance to the planning of the street canyon shape and arrangement of trees
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
