The science of windy cities

November 23, 2020

VIRTUAL MEETING (CST), November 22, 2020 -- Global population and urbanization have boomed over the last few decades. With them came scores of new tall buildings, drones, more energy-efficient ventilation systems, and planned air taxis by Uber and other companies. But these technological advancements must contend with a natural physical phenomenon: wind.

Scientists presented the latest findings on modeling and predicting urban airflow--in the hope of building better buildings, cities, and transportation--at the 73rd Annual Meeting of the American Physical Society's Division of Fluid Dynamics.

The urban skies of the future could teem with autonomous aircraft: air taxis, drones, and other self-flying systems. A team from Oklahoma State University has developed techniques to model environmental hazards these vehicles might encounter so they can safely navigate cities.

"Urban environments present enormous challenges for drone and urban air mobility platforms," said researcher Jamey Jacob, who led the team. "In addition to the challenges of traffic congestion and obstacles, critical technology gaps exist in modeling, detecting, and accommodating the dynamic urban local wind fields as well as in precision navigation through uncertain weather conditions."

Researchers attached sensors to robotic aircraft to take more cohesive measurements of building wakes, or the 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 forecasting, not only for unmanned aircraft but also for conventional airplanes.

"The potential of outfitting every drone and urban air taxi, as well as other aircraft, with sensors provides a game changing opportunity in our capability to monitor, predict, and report hazardous weather events," said Jacob.

Another group, based at the University of Surrey also investigated building wakes. With an eye toward enhancing air quality in cities, they looked for wake differences between a single tall building and a cluster of tall buildings.

"Understanding how to model the wake of tall buildings is the first step to enable city planners to reduce the heat-island effect as well as improve urban air quality," said Joshua Anthony Minien, a researcher in mechanical engineering.

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

All buildings, tall or not, must be ventilated.

"The ability to predict ventilation flow rates, purging times and flow patterns is important for human comfort and health, as highlighted by the need to prevent the airborne spread of coronavirus," said 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 through another opening.

Their mathematical modeling revealed that displacement flow does not continue during the purge of warm air, as was believed. Instead, the room experiences an "unbalanced exchange flow" which can slow down the purging process.

"Every displacement flow transitions to unbalanced exchange flow," said Wise.

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

Observations of the Urban Boundary Layer Using Autonomous Vehicles
POSTER: 3:55 p.m. CST, Monday, November 23, 2020
ABSTRACT: http://meetings.aps.org/Meeting/DFD20/Session/Q04.11
CONTACT: Jamey Jacob, jdjacob@okstate.edu

Tall Building Wakes in Isolation and in Small Clusters
POSTER: 3:55 p.m. CST, Monday, November 23, 2020
ABSTRACT: http://meetings.aps.org/Meeting/DFD20/Session/Q05.17
CONTACT: Joshua Anthony Minien, j.minien@surrey.ac.uk

Unbalanced Exchange Flow and Its Implications for the Night Cooling of Buildings
POSTER: 3:55 p.m. CST, Sunday, November 22, 2020
ABSTRACT: http://meetings.aps.org/Meeting/DFD20/Session/F15.7
CONTACT: Nicholas Wise, nhw24@cam.ac.uk

USEFUL LINKS

Meeting Website: https://dfd2020chicago.org/
Scientific Program: https://dfd2020chicago.org/program/
Registration: https://dfd2020chicago.org/registration/

Complimentary registration is available to credentialed media for the express purpose of gathering and reporting news and information from the meeting. If you have not previously obtained APS press credentials (i.e. attended other APS meetings as press or receive the APS journals tip sheet), please submit a request at http://info.aps.org/press.

ABOUT DFD

The Division of Fluid Dynamics of the American Physical Society, established in 1947, exists for the advancement and diffusion of knowledge of the physics of fluids with special emphasis on the dynamical theories of the liquid, plastic, and gaseous states of matter under all conditions of temperature and pressure.

ABOUT APS

The American Physical Society (APS) is a nonprofit membership organization working to advance and diffuse the knowledge of physics through its outstanding research journals, scientific meetings, and education, outreach, advocacy, and international activities. APS represents over 55,000 members, including physicists in academia, national laboratories, and industry in the United States and throughout the world. Society offices are located in College Park, Maryland (Headquarters), Ridge, New York, and Washington, DC.

American Physical Society

Related Aircraft Articles from Brightsurf:

University of South Carolina redefining aircraft production process
The University of South Carolina College of Engineering and Computing will transform the manufacturing and simulation processes used in aircraft production through a $5.7 million NASA grant.

Small altitude changes could cut climate impact of aircraft by up to 59%
Altering the altitudes of less than 2% of flights could reduce contrail-linked climate change by 59%, says a new Imperial study.

Small altitude changes could cut the climate impact of aircraft
Contrails -- the white, fluffy streaks in the sky that form behind planes -- can harm the environment.

New electrodes could increase efficiency of electric vehicles and aircraft
The rise in popularity of electric vehicles and aircraft presents the possibility of moving away from fossil fuels toward a more sustainable future.

Composite metal foam outperforms aluminum for use in aircraft wings
The leading edges of aircraft wings have to meet a very demanding set of characteristics.

Particulate matter from aircraft engines affects airways
In a unique, innovative experiment, researchers under the leadership of the University of Bern have investigated the effect of exhaust particles from aircraft turbine engines on human lung cells.

How to ice-proof the next generation of aircraft
To prevent ice formation on aircraft during flight, current systems utilize the heat generated by burning fuel, but these high-temperature, fuel-dependent systems cannot be used on the proposed all-electric, temperature-sensitive materials of next-generation aircraft.

Putting hybrid-electric aircraft performance to the test
Although hybrid-electric cars are becoming commonplace, similar technology applied to airplanes comes with significantly different challenges.

Aircraft microbiome much like that of homes and offices, study finds
What does flying in a commercial airliner have in common with working at the office or relaxing at home?

Sequential model chips away at mysteries of aircraft
Ice accumulation on aircraft wings is a common contributing factor to airplane accidents.

Read More: Aircraft News and Aircraft Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.