Researchers model urban airflows to help improve the design of drones, skyscrapers and natural ventilation systems

Global population and urbanization have increased in recent decades. With them came dozens of new tall buildings, drones, more energy-efficient ventilation systems, and air taxis planned by Uber and other companies. But these technological advances have to deal with a natural physical phenomenon: the wind.

Scientists presented the latest findings on urban airflow modeling and prediction in hopes of building better buildings, cities and transportation means at the American Physical Society’s 73rd Annual Meeting of Fluid Dynamics.

The urban skies of the future may be teeming with autonomous aircraft – air taxis, drones and other autonomous flight systems. A team from Oklahoma State University has developed techniques to model the environmental hazards these vehicles might encounter so they can navigate cities safely.

“Urban environments present enormous challenges for drones and urban aerial mobility platforms,” ​​said researcher Jamey Jacob, who led the team. “In addition to the challenges of traffic congestion and obstacles, there are critical technology gaps in the modeling, sensing and adaptation of dynamic urban local wind fields, as well as in precision navigation in uncertain weather conditions.”

Researchers connected sensors to robotic aircraft to make more consistent measurements of building trails or disturbed airflow around buildings. They combined this data with numerical predictions to get a better picture of the complex wind patterns found in urban environments.

The work could help improve wind and weather forecasts, not only for unmanned aircraft but also for conventional aircraft.

“The potential to equip every urban drone and air taxi, as well as other aircraft, with sensors offers a revolutionary opportunity in our ability to monitor, predict and report dangerous weather events,” said Jacob.

Another group, based at the University of Surrey, also studied the trails of buildings. With the aim of improving air quality in cities, they looked for differences in the wake between a single tall building and a group of tall buildings.

“Understanding how to model the wake of tall buildings is the first step in enabling urban planners to reduce the heat island effect and improve urban air quality,” said Joshua Anthony Minien, a researcher in mechanical engineering.

The team conducted experiments in a wind tunnel, varying the grouping, proportions and spacing of tall buildings. They were encouraged to see that, measured far enough downstream, a cluster of buildings and an isolated building have similar wake characteristics. Changes in wind direction also appear to significantly affect the wakes of building clusters.

All buildings, tall or not, must be ventilated.

“The ability to predict ventilation rates, purge times and flow patterns is important for human comfort and health, as evidenced by the need to prevent the coronavirus from airborne,” said the University of Cambridge researcher. Nicholas Wise.

With engineering professor Gary Hunt, Wise found a problem in current models of passive natural ventilation systems. These often use displacement flow, where cooler night air enters a building through one opening and warmer air accumulated during the day exits another opening.

Their mathematical modeling revealed that the displacement flow does not continue while purging the hot air, as previously believed. Instead, the room experiences an “unbalanced exchange flow” which can slow down the purging process.

“Every flow of displacement goes into an unbalanced exchange flow,” Wise said.

The researchers were surprised at how much adding a small, low-level opening accelerates the cooling of the room, compared to a room with only a high-level opening. Their model will be useful for designers of natural ventilation systems.