Clear air turbulence has long been a nuisance and a hazard to aircraft and passengers. It is invisible, unpredictable, and tends to strike when it is least welcome - during your in-flight lunch, for example.
But turbulence also occurs closer to the ground, and a better understanding of how it works would be extremely helpful to the aviation and other industries.
My research group at the Ecole Polytechnique Federale de Lausanne (EPFL) focuses on wind engineering and renewable energy, and understanding atmospheric turbulence is vital.
Wind may flow smoothly into a wind turbine, but the rotating blades that slice through the moving air stir it up into a chaotic collage of whorls - turbulence.
Since it takes time for this turbulence to die down, a second turbine further downwind will be driven by wind that hasn't yet had time to fully settle.
This process can repeat itself throughout an entire wind farm, cutting the output of downwind turbines by up to 40 per cent.
But turbulence is hard to measure. In wind farms, researchers usually rely on sensors mounted on poles or towers. But you just can't set up enough sensors at enough locations within and surrounding a wind farm to get an accurate picture of where the main whorls tend to be, how far they extend, and how long they persist.
Working with EPFL Middle East, we have developed a way to solve this conundrum using beams of bundled light - lasers.
By shooting a laser beam into the air and measuring the light reflected back by humidity or tiny particles in the atmosphere, a lidar - the laser equivalent of a radar - can provide a detailed profile of the air it traverses, almost in real time.
Last year, for the first time, we used multiple lidars to detect the three-dimensional structure of turbulence behind a real wind turbine.
These unique field measurements can be used to confirm the predictions of computer simulations of wind blowing through wind farms, and provide data that is otherwise difficult or impossible to obtain.
Turbulent phenomena are complex, and it often takes more than one single experimental method to identify and understand them.
In wind tunnel experiments we recently found that the turbulence created by wind turbines settles faster when the surrounding air is itself turbulent - such as on a hot day when the warm ground heats the air just above it, setting it in motion.
Our computer simulations under these so-called convective conditions show the same behaviour. Now we plan on studying the turbulence behind the wind turbines in Valais, Switzerland, on a hot day to see if we can confirm this phenomenon outdoors, and understand why it occurs.
In the long run, we expect a better understanding of these phenomena to lead to improved design of wind farms, taking into account not only the arrangement of the individual turbines within them, but also the surrounding topography, climate, and dominant winds, ultimately leading to more efficient exploitation of these expensive infrastructure projects.
Our ability to visualise turbulence has found applications in other fields, too.
Solar Impulse is a lightweight solar aircraft on a mission to achieve what seems impossible: to fly around the planet without a drop of fuel.
The challenge at the moment is that the plane, being developed in Switzerland, is so light that it gets bounced around by turbulence like a bird in a storm.
At high altitudes this risk can be managed, but nearer the ground, especially during take-off and landing, a bounce in the wrong direction could be dangerous.
Addressing this risk, we collaborated with Solar Impulse to develop a portable lidar-based solution to scan the air around the airfield for dangerous whorls.
Once the system gives a pilot the green light, he or she can be assured that the plane will safely descend towards the runway for landing.
Prof Fernando Porte-Agel is the director of the Wind Engineering and Renewable Energy Laboratory at EPFL in Lausanne, Switzerland
The Farewell
Director: Lulu Wang
Stars: Awkwafina, Zhao Shuzhen, Diana Lin, Tzi Ma
Four stars
The full list of 2020 Brit Award nominees (winners in bold):
British group
Coldplay
Foals
Bring me the Horizon
D-Block Europe
Bastille
British Female
Mabel
Freya Ridings
FKA Twigs
Charli xcx
Mahalia
British male
Harry Styles
Lewis Capaldi
Dave
Michael Kiwanuka
Stormzy
Best new artist
Aitch
Lewis Capaldi
Dave
Mabel
Sam Fender
Best song
Ed Sheeran and Justin Bieber - I Don’t Care
Mabel - Don’t Call Me Up
Calvin Harrison and Rag’n’Bone Man - Giant
Dave - Location
Mark Ronson feat. Miley Cyrus - Nothing Breaks Like A Heart
AJ Tracey - Ladbroke Grove
Lewis Capaldi - Someone you Loved
Tom Walker - Just You and I
Sam Smith and Normani - Dancing with a Stranger
Stormzy - Vossi Bop
International female
Ariana Grande
Billie Eilish
Camila Cabello
Lana Del Rey
Lizzo
International male
Bruce Springsteen
Burna Boy
Tyler, The Creator
Dermot Kennedy
Post Malone
Best album
Stormzy - Heavy is the Head
Michael Kiwanuka - Kiwanuka
Lewis Capaldi - Divinely Uninspired to a Hellish Extent
Dave - Psychodrama
Harry Styles - Fine Line
Rising star
Celeste
Joy Crookes
beabadoobee
Third Test
Day 3, stumps
India 443-7 (d) & 54-5 (27 ov)
Australia 151
India lead by 346 runs with 5 wickets remaining
UPI facts
More than 2.2 million Indian tourists arrived in UAE in 2023
More than 3.5 million Indians reside in UAE
Indian tourists can make purchases in UAE using rupee accounts in India through QR-code-based UPI real-time payment systems
Indian residents in UAE can use their non-resident NRO and NRE accounts held in Indian banks linked to a UAE mobile number for UPI transactions
Simran
Director Hansal Mehta
Stars: Kangana Ranaut, Soham Shah, Esha Tiwari Pandey
Three stars
COMPANY PROFILE
Name: Xpanceo
Started: 2018
Founders: Roman Axelrod, Valentyn Volkov
Based: Dubai, UAE
Industry: Smart contact lenses, augmented/virtual reality
Funding: $40 million
Investor: Opportunity Venture (Asia)
CREW
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The biog
Hobby: Playing piano and drawing patterns
Best book: Awaken the Giant Within by Tony Robbins
Food of choice: Sushi
Favourite colour: Orange
The White Lotus: Season three
Creator: Mike White
Starring: Walton Goggins, Jason Isaacs, Natasha Rothwell
Rating: 4.5/5
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Key facilities
- Olympic-size swimming pool with a split bulkhead for multi-use configurations, including water polo and 50m/25m training lanes
- Premier League-standard football pitch
- 400m Olympic running track
- NBA-spec basketball court with auditorium
- 600-seat auditorium
- Spaces for historical and cultural exploration
- An elevated football field that doubles as a helipad
- Specialist robotics and science laboratories
- AR and VR-enabled learning centres
- Disruption Lab and Research Centre for developing entrepreneurial skills
From Zero
Artist: Linkin Park
Label: Warner Records
Number of tracks: 11
Rating: 4/5
The rules on fostering in the UAE
A foster couple or family must:
- be Muslim, Emirati and be residing in the UAE
- not be younger than 25 years old
- not have been convicted of offences or crimes involving moral turpitude
- be free of infectious diseases or psychological and mental disorders
- have the ability to support its members and the foster child financially
- undertake to treat and raise the child in a proper manner and take care of his or her health and well-being
- A single, divorced or widowed Muslim Emirati female, residing in the UAE may apply to foster a child if she is at least 30 years old and able to support the child financially
Afcon 2019
SEMI-FINALS
Senegal v Tunisia, 8pm
Algeria v Nigeria, 11pm
Matches are live on BeIN Sports