Effects of tree geometry on the aerodynamics of sympodial trees with analysis of extreme gust wind

Trees are among the species most severely affected in coastal regions when storms strike. However, there remains no definitive explanation how the tree geometry affects wind loading of trees. The wind loading of 3-order sympodial tree models with four distinct tree geometry, were thoroughly investigated through wind tunnel experiments in this study. The results show that the tree model with lower branch angles shows lower drag coefficient, while the tree model with higher branch angles shows a lower overturning moment coefficient. Meanwhile, the tree model with lower surface density or weak branch collisions can lead to a faster reduction in wind loading. Subsequently, the tree model with higher branch orders have been confirmed to have a lower drag coefficient and overturning moment coefficient. Then, the effect of extreme gust wind in urbanized areas on the tree models is investigated. Finally, spectral analysis is adopted to reveal the vibration characteristics under uniform wind flow and extreme-gust wind flow.