Understanding urban fluid flows urgent for dispersing pollution

Approximately 90 percent of the urban population in the European Union is exposed to air pollution levels that exceed those recommended by the World Health Organization. And the EU is by no means alone. Improving air quality is critical for preventing health problems worldwide, but that requires an understanding of how air flows in cities.

In an effort to improve this essential knowledge base, Lazpita et al. studied the behavior of a turbulent flow in an urban environment consisting of two adjacent buildings. They specifically investigated arch vortices, which form on the leeward side of one of the buildings as a consequence of the interaction between the outer flow and the urban-canopy layer.

The team analyzed a large database with higher-order dynamic mode decomposition. While classical approaches only obtain statistical information on air flow, this procedure can identify the most relevant flow structures.

“We have been able to identify some flow structures that are possibly related to creating and destroying the arch vortex,” said author Sergio Hoyas. “This identification is a crucial point to understanding the behavior of the flow and thus controlling it.”

While the decomposition technique provides valuable information, it does not capture the entire picture. The researchers aim to use artificial intelligence to look at instantaneous coherent structures and see how the arch vortex influences passive scalars in the air flow.

“This vortex is thought to be responsible for contaminant concentration in cities,” said Hoyas. “This identification can be the first step to facilitating their control and thus improving contaminants’ dispersion.”

Source: “On the generation and destruction mechanisms of arch vortices in urban fluid flows,” by Eneko Lazpita, Álvaro Martínez-Sánchez, Adrián Corrochano, Sergio Hoyas, Soledad Le Clainche, and R. Vinuesa, Physics of Fluids (2022). The article can be accessed at https://doi.org/10.1063/5.0088305 .