Urban canyon models gain an extra dimension

Cities have unique climates; the tall buildings create “urban canyons” where airflow is confined and redirected in unusual ways. These canyons can trap heat, produce or curtail winds, and create wildly varying microclimates that affect the people on the ground. Understanding the interaction between heat and airflow within urban canyons will help city planners design better street layouts and zoning plans.

Zhao et al. used wind tunnel experiments and particle image velocimetry (PIV) to study urban canyon flows in two and three dimensions. Their goal was to provide more realistic data than previously existed.

“While most previous research focused on idealized 2D models, real urban streets are inherently 3D,” said author Chongyu Zhao. “There was a significant lack of high-resolution experimental data showing how ground heating actually affects complex 3D flow structures, like lateral flows and corner eddies.”

The authors subjected both their 2D and 3D canyons to matched conditions, using PIV data to study their differences. They found that while 2D canyons quickly develop an organized air circulation driven by heating and buoyancy, the 3D canyon exhibits lateral airflow and corner eddies that disrupt the upward movement of air. This disruption redistributes heat and momentum, leading to variable and intermittent airflow even under strong heating conditions.

In the future, this data could be used to inform computational simulations, letting researchers incorporate 3D effects into their models.

“Ultimately, by improving these computer models, urban planners will have more accurate tools to design street layouts that effectively manage ventilation and air quality,” said Zhao.

Source: “Three-dimensional effects and turbulence characteristics in heated urban canyons,” by Chongyu Zhao, Ximeng Kang, Ozgun Ozer, David Topping, Ben Parslew, and Shan Zhong, Physics of Fluids (2026). The article can be accessed at https://doi.org/10.1063/5.0342740 .