Wings that waggle airflow could cut aviation bills 20%

Wings that waggle airflow, directing it sideways, could cut down airline fuel usage by 20 percent because of research funded by the Engineering and Physical Sciences Research Council and Airbus in the UK.

Associate Professor Duncan Lockerby, with Coventry, UK-based University of Warwick, told the Cleantech Group today that he’s exploring a new approach to reducing mid-flight drag through tiny air-powered jets that redirect air, making it flow perpendicular to the direction of motion. He envisions “hundreds of thousands of jets of air potentially over the surface of the aircraft.”

Warwick has received £1 million ($1.6 million) for the three-year project to better understand the physical mechanisms of the process and progress the technology.

“People have found, not just us, that if in general you move air flow in a direction that’s perpendicular to the direction of travel, back and forth, you can actually reduce drag,” he said.

Most passengers can feel large-scale airline turbulence, Lockerby said.

“There’s also small-scale turbulence close to the wing’s surface that creates a lot of drag that you’re fighting against when you are burning fuel. We’re trying to understand if you create oscillation in air flows in a perpendicular direction [whether] it reduces the level of turbulence very near to the aircraft,” he said.

The jets work according to the Helmholtz resonance principle—when air is forced into a cavity the pressure increases, which forces air out and sucks it back in again, causing an oscillation—similar to when air is blown over the orifice of a bottle.

“We’re trying to exploit this blowing-over-a-bottle effect,” said Lockerby, who works in the University of Warwick’s Fluid Dynamics Research Centre in the School of Engineering and holds a doctorate in computational fluid dynamics.

“When you are in cruise [control mode], you are burning fuel mainly to overcome drag. If you reduce drag 20 percent, you could reduce the fuel you need to consume by 20 percent and thereby emissions,” he added.

The Advisory Council for Aerospace Research in Europe set a target of a 50-percent reduction in carbon dioxide emissions per passenger kilometer by 2020, an 80-percent cut in nitrogen oxides and a 50-percent reduction in noise. These savings are expected to come from lighter aircraft as well as engine improvements and fuel economies. Drag friction is another major factor in fuel consumption.

The research is still in the conceptual stage, but Lockerby said they are looking at trying the new concept with power jets in wind tunnel tests. They’ll look first at active devices and then more passive devices, where no power is required. The discovery has come as a surprise to the aerodynamics community, Lockerby said, as it was discovered "by waggling a piece of wing from side to side in a wind tunnel."

Engineers have long known that tiny ridges called “riblets” can reduce skin-friction drag (a major portion of mid-flight drag) by 5 percent. The micro-jet systems Lockerby and his colleagues are developing could reduce skin-fraction drag by as much as 40 percent.

The research is being conducted in conjunction with Cardiff University, Imperial College London, Sheffield College and Queen’s University Belfast. New wings could be ready for trials by 2012.

Airline manufacturers would likely be interested in the technology, Lockerby said, and companies such as Boeing have done research and development in this area.

Boeing has also been exploring new technology options for environmentally progressive aerospace products including an airplane power by hydrogen fuel cells (see Boeing tests fuel cell-powered plane).

Beyond its aerospace relevance, Lockerby’s development could be applied in other forms of high speed or marine transportation, as other engineers are also pursing. An Indian engineer released a study that provides a way using active flow control to reduce the drag on cars and trucks by up to 18 percent. The professor’s work placed actuators on the surface of vehicles to reduce resistance by modifying airflow (see Reducing drag to improve gas mileage).

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