̽��ֱ�� of Cambridge - turbine

̽��ֱ��owl and the wind turbine: how stealth feathers could help reduce noise pollution

amb206 — Wed, 09 Sep 2015 13:54:14 +0000

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Owls fly silently: not all species of owl but those species that rely on stealth in hunting small animals. People have known this for hundreds of years but until recently no-one has understood quite how these magical birds manage to swoop undetected on their scurrying prey.

̽��ֱ��puzzle of how the wings of certain species of owls are adapted to minimise the sound that their wings make has been solved by a partnership between researchers at the ̽��ֱ�� of Cambridge and two institutions in the USA.

̽��ֱ��key to the puzzle lies in the intricate structure of owls’ feathers – and especially the plumage on the trailing edge of their wings.

̽��ֱ��researchers have now been able to replicate this structure by producing a prototype surface (patented in 2014) which has potential applications in wind turbines and a wide range of fans. Its use could significantly reduce the noise generated by these products.

An especially promising end-use for the surface is for on-shore wind turbines which are heavily ‘braked’ to reduce noise pollution. ̽��ֱ��braking makes the turbines less efficient.

̽��ֱ��story began in 2010 when Dr Justin Jaworksi, then a researcher in the Department of Applied Mathematics and Theoretical Physics (DAMTP) at Cambridge ̽��ֱ��, decided to look in detail at the structure of owls’ wings.

At DAMTP, Jaworski (who is now at Lehigh ̽��ֱ��) worked with Professor Nigel Peake, a specialist in aeroacoustics known for his work on aircraft, to identify how owls’ wings differed from those of other birds.

They found three key differences. ̽��ֱ��first difference, unrelated to silent flight, is that owls’ wings are have a serrated leading edge in a way that enables them to plunge steeply downwards and then take off again.

̽��ֱ��other two differences combine to enable owls to fly stealthily so that they can hear their prey without it hearing them. “ ̽��ֱ��feathers on the upper wing surface have a particularly detailed and complex micro-structure with layer upon layer of interleaved barbs and hairs,” said Peake.

Much of the noise from wings – whether the wing of bird, plane or fan – originates at the trailing edge where the air passing over the wing surface becomes suddenly turbulent.

Owls have a neat solution to this problem. “At the trailing edge of their wings, owl feathers produce a flexible and porous fringe which reduces air turbulence by smoothing the passage of air,” said Peake.

No other species of bird possesses these features. Even more significantly, species of owl (such as fish owls) not requiring an acoustic stealth advantage do not possess them either.

To understand how the features unique to owl wings contribute to soundlessness, and in order to replicate the surfaces created, Jaworski and Peake have been collaborating with Professors William Devenport at Virginia Tech and Stewart Glegg at Florida Atlantic ̽��ֱ�� in a project funded by the US Office of Naval Research.

“We used advanced mathematical tools in a wind tunnel to show that the role of the fringe on owls’ wings is to negate something called the ‘Flowes Williams and Hall effect’. ̽��ֱ��porous elastic fringe filaments are a much softer ‘sound scatterer’ than a sharp rigid edge,” said Peake.

̽��ֱ��role of the complex feather structure is more of a mystery but the collaborators have been able, to some extent, to replicate its effect in the laboratory. “What appears to be crucial is the way that the fine hairs form a ‘canopy’ perhaps shielding the basal surface of the wing from pressure fluctuations in the turbulent air flow,” said Peake.

" ̽��ֱ��whole project has been very exciting. We’ve been able to use advanced mathematics to understand an amazing natural phenomenon, which then inspired us to develop a practical engineering solution to a really challenging noise pollution problem."

̽��ֱ��intricate structure of owl’s wings was noted more than 300 years ago by Francis Willughby (1635 to 1672), the polymath who compiled one of the world’s first comprehensive and analytical ornithologies. Several species of owl feature in Willughby’s Ornithologia libri tres which was published by his more famous friend and colleague John Ray (1627 to 1705).

Willughby studied at Trinity College, Cambridge, where the Wren Library holds a copy of the ornithology he authored. ̽��ֱ��lavishly produced volume contains dozens of plates showing birds categorised by their characteristics. ̽��ֱ��accompanying text reveals Willughby’s passionate interest in the wonders of the natural world.

Of the eagle-owl, Willughby writes: “ … in the great feathers of the Wings and Tail distinguished with broad, transverse, blackish lines or bars; which lines are so formed, especially in the Tail, that each of the broader are terminated above and below by other narrower ones, like borders or fringes, disposed in a triple order, and at certain intervals distant from each other, as in Hawks.”

Next in the Cambridge Animal Alphabet: P is for critters that are part of one of the most significant of all human-animal relationships.

Have you missed the series so far? Catch up on Medium here.

Inset images: Barn owl in flight (Chris Thompson); Barn Owl (Pat Gaines); Owls from Ornithologia libri tres by Francis Willughby (Wren Library, Trinity College).

The Cambridge Animal Alphabet series celebrates Cambridge's connections with animals through literature, art, science and society. Here, O is for Owl, the researchers using their wing structure to inspire aeroacoustic developments, and the lavish drawings of them found in one of the world's first ornithologies.

We’ve been able to use advanced mathematics to understand an amazing natural phenomenon, which then inspired us to develop a practical engineering solution

Nigel Peake

Wren Library, Trinity College

Small Owl from Ornithologia libri tres by Francis Willughby

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes

From atoms to jet engines – extreme materials on display at summer exhibition

Anonymous — Tue, 30 Jun 2015 10:02:07 +0000

̽��ֱ��ever-increasing demand for air travel while simultaneously reducing carbon emissions constitutes a huge engineering challenge. Greater efficiency requires engines to run hotter and faster, but today’s best materials are already running close to their limits.

̽��ֱ��metals inside a jet engine must operate in a gas stream about a third as hot as the sun’s surface while enduring centrifugal forces equivalent to hanging a double-decker bus from each turbine blade.

At the ̽��ֱ�� of Cambridge, researchers are designing new alloys that are able to withstand even more extreme conditions of stress and temperature, as Dr Cathie Rae at the Cambridge Rolls-Royce ̽��ֱ�� Technology Centre (UTC) explains: “In jet engines, we currently use special metals called superalloys that are created by mixing together nickel with other elements.

“They are called superalloys because they exhibit exceptional high-temperature mechanical properties and resistance to corrosion. In fact, they actually get stronger as we heat them up. We’re trying to make materials that are even better than these superalloys!”

Visitors to the Engineering Atoms exhibit at the Royal Society Summer Science Exhibition from 30 June until 5 July will be able to see how the atomic structure of materials affects their properties, and will be able to handle real jet engine components.

In the Rolls-Royce UTC, scientists work in close collaboration with one of the world’s leading engine manufacturers, Rolls-Royce plc, and the Engineering and Physical Sciences Research Council (EPSRC) to design and make new high-temperature materials. To achieve this, they need to understand everything from the shape and design of the component right down to the behaviour of individual atoms in the metal. By engineering the arrangement of the atoms, varying their type, position and size, researchers can radically change how these metals perform.

This involves the use of powerful microscopes that use electrons instead of optical light to examine materials on the atomic scale. By using these electron microscopes, researchers can look at individual rows of atoms and identify their composition. ̽��ֱ��Engineering Atoms stand will have a working scanning electron microscope, the Phenom ProX, so visitors will be able to look at alloys on the micrometre scale.

Engineering Atoms will also be exhibiting amazing materials that ‘remember’ their original shape after they’ve been deformed. These ‘shape-memory’ alloys, made from titanium and nickel, can be used to control and optimise airflow in jet engines where conventional hydraulic or electrical control systems would be difficult to operate.

̽��ֱ��Summer Science Exhibition will be open to the public from 30 June to 5 July 2015.

At any one time over half a million people are flying far above our heads in modern aircraft. Their lives depend on the performance of the special metals used inside jet engines, where temperatures can reach over 2000˚C. Cambridge researchers will be exhibiting these remarkable materials at this year’s Royal Society Summer Science Exhibition.

In jet engines, we currently use special metals called superalloys that exhibit exceptional high-temperature mechanical properties and resistance to corrosion

Cathie Rae

Engineering Atoms

̽��ֱ�� of Cambridge

A jet engine turbine blade.

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes

Engineering atoms inside the jet engine: the Great British Take Off

lw355 — Mon, 29 Jun 2015 07:30:21 +0000

Inside a jet engine is one of the most extreme environments known to engineering.

In less than a second, a tonne of air is sucked into the engine, squeezed to a fraction of its normal volume and then passed across hundreds of blades rotating at speeds of up to 10,000 rpm; reaching the combustor, the air is mixed with kerosene and ignited; the resulting gases are about a third as hot as the sun’s surface and hurtle at speeds of almost 1,500 km per hour towards a wall of turbines, where each blade generates power equivalent to the thrust of a Formula One racing car.

Turbine blades made from ‘super’ materials with outstanding properties are needed to withstand these unimaginably challenging conditions – where the temperatures soar to above the melting point of the turbine components and the centrifugal forces are equivalent to hanging a double-decker bus from each blade.

Even with these qualities, the blades require a ceramic layer and an air cooling system to prevent them from melting when the engine reaches its top temperatures. But with ever-increasing demands for greater performance and reduced emissions, the aerospace industry needs engines to run even hotter and faster, and this means expecting more and more from the materials they are made from.

This, says Dr Cathie Rae, is the materials grand challenge. “Turbine blades are made using nickel-based superalloys, which are capable of withstanding the phenomenal stresses and temperatures they need to operate under within the jet engine. But we are running close to their critical limits.”

An alloy is a mixture of metals, such as you might find in steel or brass. A superalloy, however, is a mixture that imparts superior mechanical strength and resistance to heat-induced deformation and corrosion.

Rae is one of a team of scientists in the Rolls-Royce ̽��ֱ�� Technology Centre (UTC) at the Department of Materials Science and Metallurgy. ̽��ֱ��team’s research efforts are focused on extracting the greatest possible performance from nickel-based superalloys, and on designing superalloys of the future.

Current jet engines predominantly use alloys containing nickel and aluminium, which form a strong cuboidal lattice. Within and around this brick-like structure are up to eight other components that form a ‘mortar’. Together, the components give the material its superior qualities.

“Even tiny adjustments in the amount of each component can have a huge effect on the microscopic structure, and this can cause radical changes in the superalloy’s properties,” explains Dr Howard Stone. “It’s rather like adjusting the ingredients in a cake – increasing one ingredient might produce one sought-after property, but at the sake of another. We need to find the perfect chemical recipe.”

Stone is the Principal Investigator overseeing a £50 million Strategic Partnership on structural metallic systems for advanced gas turbine applications funded jointly by Rolls-Royce and the Engineering and Physical Sciences Research Council (EPSRC), and involving the Universities of Birmingham, Swansea, Manchester, Oxford and Sheffield, and Imperial College London.

̽��ֱ��researchers melt together precise amounts of each of the different elements to obtain a 5cm bar, then exhaustively test the bar’s mechanical properties and analyse its microscopic structure. Their past experience in atomic engineering is vital for homing in on where the incremental improvements might be found – without this, they would need to make many millions of bars to test each reasonable mixture of components.

Now, they are looking beyond the usual components to exotic elements, although always with an eye on keeping costs as low as possible, which means not using extremely rare materials. “ ̽��ֱ��Periodic Table is our playground… we’re picking and mixing elements, guided by our computer models and experimental experience, to find the next generation of superalloys,” he adds.

̽��ֱ��team now have 12 patents with Rolls-Royce. One of the most recent has been in collaboration with Imperial College London, and involves the discovery that the extremely strong matrix structure of nickel-based aluminium superalloys can also be achieved using a mixture of nickel, aluminium, cobalt and tungsten.

“Instead of the cake being flavoured with two main ingredients, we can make it with four,” Stone explains. “This gives the structure even better properties, many of which we are only just discovering.”

“We’ve also been looking at new intermetallic reinforced superalloys using chromium, tantalum and silicon – no nickel at all. We haven’t quite got the final balance to achieve what we want, but we’re working towards it.”

Stone highlights the importance of collaboration between industry and academia: “New alloys typically take 10 years and many millions of pounds to develop for operational components. We simply couldn’t do this work without Rolls-Royce. For the best part of two decades we’ve had a collaboration that links fundamental materials research through to industrial application and commercial exploitation.”

It’s a sentiment echoed by Dr Justin Burrows, Project Manager at Rolls-Royce: “Our academic partners understand the materials and design challenges we face in the development of gas turbine technology. Improvements like the novel nickel and steel alloys developed in Cambridge are key to helping us meet these challenges and to maintaining our competitive advantage.”

̽��ֱ��Cambridge UTC, which was founded by its Director Professor Sir Colin Humphreys in 1994, is one of a global network of over 30 UTCs. These form part of Rolls-Royce’s £1 billion annual investment in research and development, which also includes the Department of Engineering’s ̽��ֱ�� Gas Turbine Partnership. Rolls-Royce and EPSRC also fund Doctoral Training Centres in Cambridge that help to ensure a continuing supply of highly trained scientists and engineers ready to move into industry.

̽��ֱ��UK aerospace industry is the largest in Europe, with a turnover in 2011 of £24.2 billion; worldwide, it’s second only to that of the USA. Meanwhile, increasing global air traffic is estimated to require 35,000 new passenger aircraft by 2030, worth about $4.8 trillion.

For the researchers, it’s fascinating to see global engineering challenges being solved from the atom up, as Rae explains: “ ̽��ֱ��commercial success of a new engine can be dependent on very small differences in fuel efficiency, which can only be achieved by innovations in materials and design. There’s something really exciting about working at the atomic scale and seeing this translate into innovation with big powerful machines.”

Inset image: Thermo cycling.

̽��ֱ��Periodic Table may not sound like a list of ingredients but, for a group of materials scientists, it’s the starting point for designing the perfect chemical make-up of tomorrow’s jet engines.

Increasing one ingredient might produce one sought-after property, but at the sake of another – we need to find the perfect chemical recipe

Howard Stone

Engineering Atoms

Rolls-Royce Plc

Rotor

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes

Silent flights: How owls could help make wind turbines and planes quieter

sc604 — Sun, 21 Jun 2015 23:03:07 +0000

An investigation into how owls fly and hunt in silence has enabled researchers to develop a prototype coating for wind turbine blades that could significantly reduce the amount of noise they make.

Early tests of the material, which mimics the intricate structure of an owl’s wing, have demonstrated that it could significantly reduce the amount of noise produced by wind turbines and other types of fan blades, such as those in computers or planes. Since wind turbines are heavily braked in order to minimise noise, the addition of this new surface would mean that they could be run at much higher speeds – producing more energy while making less noise. For an average-sized wind farm, this could mean several additional megawatts worth of electricity.

̽��ֱ��surface has been developed by researchers at the ̽��ֱ�� of Cambridge, in collaboration with researchers at three institutions in the USA. Their results will be presented today (22 June) at the American Institute of Aeronautics and Astronautics (AIAA) Aeroacoustics Conference in Dallas.

“Many owls – primarily large owls like barn owls or great grey owls – can hunt by stealth, swooping down and capturing their prey undetected,” said Professor Nigel Peake of Cambridge’s Department of Applied Mathematics and Theoretical Physics, who led the research. “While we’ve known this for centuries, what hasn’t been known is how or why owls are able to fly in silence.”

Peake and his collaborators at Virginia Tech, Lehigh and Florida Atlantic Universities used high resolution microscopy to examine owl feathers in fine detail. They observed that the flight feathers on an owl’s wing have a downy covering, which resembles a forest canopy when viewed from above. In addition to this fluffy canopy, owl wings also have a flexible comb of evenly-spaced bristles along their leading edge, and a porous and elastic fringe on the trailing edge.

“No other bird has this sort of intricate wing structure,” said Peake. “Much of the noise caused by a wing – whether it’s attached to a bird, a plane or a fan – originates at the trailing edge where the air passing over the wing surface is turbulent. ̽��ֱ��structure of an owl’s wing serves to reduce noise by smoothing the passage of air as it passes over the wing – scattering the sound so their prey can’t hear them coming.”

In order to replicate the structure, the researchers looked to design a covering that would ‘scatter’ the sound generated by a turbine blade in the same way. Early experiments included covering a blade with material similar to that used for wedding veils, which despite its open structure, reduced the roughness of the underlying surface, lowering surface noise by as much as 30dB.

While the ‘wedding veil’ worked remarkably well, it is not suitable to apply to a wind turbine or aeroplane. Using a similar design, the researchers then developed a prototype material made of 3D-printed plastic and tested it on a full-sized segment of a wind turbine blade. In wind tunnel tests, the treatment reduced the noise generated by a wind turbine blade by 10dB, without any appreciable impact on aerodynamics.

While the coating still needs to be optimised, and incorporating it onto an aeroplane would be far more complicated than a wind turbine, it could be used on a range of different types of wings and blades. ̽��ֱ��next step is to test the coating on a functioning wind turbine. According to the researchers, a significant reduction in the noise generated by a wind turbine could allow them to be spun faster without any additional noise, which for an average-sized wind farm, could mean several additional megawatts worth of electricity.

̽��ֱ��research was funded by the US National Science Foundation and the US Office of Naval Research.

Inset image: Close-up view of a flight feather of a Great Grey Owl. Credit: J. Jaworski.

Homepage image: Owl, by Mirko Zammarchi via Creative Commons

A newly-designed material, which mimics the wing structure of owls, could help make wind turbines, computer fans and even planes much quieter. Early wind tunnel tests of the coating have shown a substantial reduction in noise without any noticeable effect on aerodynamics.

No other bird has this sort of intricate wing structure

Nigel Peake

m01229

Flying snowy owl

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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