High-Resolution CFD Analysis of LiDAR-Reconstructed Camphor Trees on Urban Thermal Comfort and Air Quality

Accurate evaluation of the thermal and ventilation effects of urban trees remains challenging due to the difficulty of representing fine-scale tree morphology in computational models. This study aims to develop a generalized hydrodynamic framework capable of capturing realistic tree structural characteristics and assessing their impacts on airflow and pollutant dispersion in urban street canyons. High-resolution light detection and ranging (LiDAR) point cloud data of camphor trees were acquired to reconstruct detailed crown geometry, and an algorithm was developed to map individual leaves onto the computational grid. A mathematical model incorporating airflow resistance and convective heat transfer under realistic leaf area distribution was established and validated. At low incoming wind velocity, due to the non-uniform crown shape and leaf arrangement, both the vortex structure and the location of the vortex center vary across different cross-sections. With decreasing canopy temperature, the maximum mean the absolute value of normalized pollutant concentration at pedestrian breathing height decreased by 6.39. When the temperature difference increases from 1 K up to 4 K, the leeward-side wind velocity rises to 0.32 m s−1. When a temperature difference existed between the canopy and the ambient air and the wall surface was heated, variations in flow patterns and normalized pollutant concentrations within the canopy-covered sections (y = 0 and y = − 2 m) were insignificant. In contrast, geothermal energy exhibits the most significant pollutant removal effect on the leeward side, with the absolute value of the normalized pollutant concentration decreasing by 7.56. Other heating methods exert a smaller influence, with the absolute value of the normalized pollutant concentration change not exceeding 2.98 on the windward side or 0.69 on the leeward side. When the wind direction is parallel to the street canyon axis, the normalized pollutant concentration is no longer influenced by changes in leaf area density (LAD). The proposed framework enables fine-scale evaluation of real-tree effects on airflow modification and pollutant removal.