How urban trees work together to dissipate wind energy

Trees play an important role in urban micrometeorology, particularly in shielding their neighborhoods from wind. But how neighboring trees affect one another is rarely considered, in part because it’s so difficult to study: Wind tunnel experiments are too large, and scaled models, like bonsai trees, shrink the wake’s turbulence scale, making the measurement challenging.

Yin et al. conducted a large-scale, high-fidelity numerical study of downstream tree wakes and how the trees’ spacing affects turbulence, energy dissipation, and drag to address this information gap for creating accurate tree models.

“People still know little about their [trees’] fluid mechanics characteristics, especially energy dissipation behavior in the wake region,” said author Yuwei Yin.

The researchers uncovered an intricate relationship between the spacing of the trees and their combined energy dissipation. They expected that after a certain threshold gap between the trees, the downstream wake would eventually settle at an equilibrium dissipation. Instead, they found that regardless of the spacing, the energy dissipation coefficient within the tree’s near wake region is never constant.

“This is crucial because, to our knowledge, current urban micrometeorology simulations that incorporate trees typically assume a constant dissipation coefficient,” said Yin.

More than 3 billion grid points were used in the simulations, in which the heights of the two trees were the same, but their spacing ranged from twice to eight times their height. The group plans to extend this study to better understand why the tree spacing does not significantly alter the downstream trees’ dissipation.

Yin says they hope these findings will provide a scientific basis for wind safety in urban planning and micrometeorology.

Source: “Non-equilibrium dissipation in paired fractal-tree turbulence,” by Yuwei Yin, Ryo Onishi, Seiya Watanabe, Koji Nagata, and Takayuki Aoki, Physics of Fluids (2025). The article can be accessed at https://doi.org/10.1063/5.0282722 .