Information on the wind load acting on an individual tree is essential to assess the risk of tree failures in urban landscapes. Numerical simulation is one of the approaches to predict the wind loads. Although a porous media approximation of the tree volume - with associated momentum sink and turbulence source terms - is known to simulate the impact of trees on the wind flow, a lack of knowledge exists when it comes to predicting the drag force on the trees. In this study, three-dimensional steady state Reynolds-Averaged Navier-Stokes simulations are performed of a scaled, procedurally grown L-System tree in a wind tunnel, represented in the simulations by a porous media zone. It is found that the influence of porous region geometry, i.e., ellipsoid or cuboid, on the drag force prediction is very small and can be neglected. The difference in using the leaf area density, plant area density and frontal silhouette area density of the scaled fractal tree model as a parameter to the porous-media model formulae is analyzed. In addition, the effect of a height-varying leaf area density is also analyzed and discussed, as well as the effect of including the tree-trunk in the model. Eventually, the simulation results exhibit a 19% over-prediction on the drag force; while a good match of the normalized velocity profiles is obtained at the tree leeward sides.
License type:
http://creativecommons.org/licenses/by-nc-nd/4.0/
Funding Info:
The authors gratefully acknowledge the financial support of the research grant under Virtual Singapore Programme (NRF2017VSG-AT3DCM001-029) from the National Research Foundation of Singapore.