Predicting air turbulence is almost like catching the wind



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