Modulating local winds and turbulence around a single building obstacle with the obstruction of tall vegetation.

This article investigates how the positioning of tall vegetation (trees) relative to a single building influences urban airflow and turbulence within residential zones, using building-resolving large-eddy simulation (LES) with the PALM modeling system. The study compares scenarios with trees placed upstream, downstream, or absent (treeless) and finds that upstream vegetation significantly disrupts flow patterns, alters vertical wind profiles, and modifies wake circulations more than downstream vegetation. Upstream trees create a distinct shear layer at canopy height that affects turbulent kinetic energy (TKE) on both windward and leeward sides of the building, shifting TKE profile inflection points by up to 0.13 times the building height (H), while smaller tree-building separations cause the building and tree to act as a single aerodynamic barrier. Spectral analyses reveal that upstream vegetation leads to higher power spectral densities of streamwise turbulence within the residential area, with small-scale spanwise velocity fluctuations energetic near the building's windward side and large-scale eddies dominating the wake region. These findings highlight the importance of strategic vegetation placement in urban planning to modulate local wind environments and ventilation, with implications for air quality and thermal comfort.