Dispersion and transport of wind-driven tree pollen in urban environments are indispensable for assessing potential aeroallergen exposure and associated public health impacts. Resolving urban airflow interactions with trees using computational fluid dynamics (CFD) remains a significant challenge, as it necessitates the development of advanced tree-scale aerodynamic resistance models and continuum representations that realistically capture wind-induced pollen detachment and dispersion dynamics. A new direct-forcing porous immersed boundary method (DF-PIBM) is developed to explore the wind-driven pollen dispersion and transport phenomena from green trees. This framework provides a comprehensive numerical assessment of the impact of tree leaf area density on pollen detachment, dispersion, and wake-driven transport in an urban atmospheric flow. The DF-PIBM is validated across multiple flow configurations, including (i) two-dimensional (2D) fluid flow past an impermeable cylinder at a Reynolds number Re=40, (ii) three-dimensional (3D) flow past an impermeable sphere at Re=104, (iii) 3D flow past a porous sphere at Re=1200, and (iv) pressure field inside a permeable sphere for a 3D flow at Re=100. This is in addition to (v) quantitative comparison with experimental measurements reported in the literature for wind flow over and around a real oak tree, e.g., situated in open terrain under an averaged incoming wind speed of u∞=28.8 km/h. The present DF-PIBM CFD framework demonstrates substantial potential for predicting the detachment, dispersion, resuspension, and transport of airborne pollen grains, in addition to supporting various other future applications involving vegetation–flow interactions in urban settings.
Dbouk et al. (Sun,) studied this question.