2024/11/03 by Dipanjan Majumdar, Giulio Vita, Majumdar, Dipanjan +7
Engineering · Environmental Science · #FOS: Physical sciences #Fluid Dynamics (physics.flu-dyn) #Forest Biomass Utilization and Management #Forest ecology and management #Tree Root and Stability Studies
paper · pdf · doi:10.48550/arxiv.2411.01570
openalex publication_date 2024/11/03 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
The effects of trees on urban flows are often determined using computational fluid dynamics approaches which typically use a quadratic drag formulation based on the leaf-area density a and a volumetric drag coefficient CdV to model vegetation. In this paper, we develop an analytical model for the flow within a vegetation canopy and identify that the drag length ℓd = (a CdV)-1 is the key metric to describe the local tree drag characteristics. A detailed study of the literature suggests that the median ℓd observed in field experiments is 21 m for trees and 0.7 m for low vegetation (crops). A total of 168 large-eddy simulations are conducted to obtain a closed form of the analytical model. The model allows determining a and CdV from wind-tunnel experiments that typically present the drag characteristics in terms of the classical drag coefficient Cd and the aerodynamic porosity αL. We show that geometric scaling of ℓd is the appropriate scaling of trees in wind tunnels. Evaluation of ℓd for numerical simulations and wind-tunnel experiments (assuming geometric scaling 1:100) in literature shows that the median ℓd in both these cases is about 5 m, suggesting possible overestimation of vegetative drag.