Fractal simulations reveal that urban trees enter a state of "drag crisis" to survive high winds.
March 31, 2026
Original Paper
Drag Crisis in Fractal Trees Revealed by Simulation and Theory
arXiv · 2603.27954
The Takeaway
A 'drag crisis' is a sudden, counter-intuitive drop in air resistance that usually happens to smooth objects like golf balls at high speeds. This study shows that the complex, fractal branching of trees allows them to hit this transition early, effectively 'shedding' wind force to prevent branches from snapping during storms.
From the abstract
Trees are key roughness elements in urban environments, shaping airflow, microclimates, and pollutant dispersion. Yet the aerodynamic drag of complex tree-like structures at high Reynolds numbers remains poorly characterized compared with the well-studied drag crisis of simple bluff bodies. We combine large-scale lattice Boltzmann simulations with an analytical branch-wise drag model to examine fractal trees over a wide range of height-based Reynolds numbers, $Re_H$. Direct numerical simulations