Shape-shifting skin for planes and submarines would provide lesser turbulence

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Washington, April 17 : Engineers have tested designs for an "active skin" for planes and submarines, which can change at a flick of a button and provide lesser turbulence.

According to a report in New Scientist, Dimitris Lagoudas at Texas A and M University, US, and his team, developed the new designs.

Turbulence is a big problem for engineers as chaotic air flow sets up unstable vortices and patterns in gases and liquids, increasing friction and drag.

"Giving craft skin than can tweak its surface to impose order on these currents could dramatically cut the effect of drag," said Lagoudas.

Lagoudas and colleagues have worked out that wrinkling the surface of a craft in the right way can cut problems.

The surface must assume the shape of the ideal ordered surface wave it is trying to create, something that changes at different velocities.

It might seem counterintuitive to reduce drag by wrinkling the surface of a craft, but nature provides a precedent. "Dolphins induce their skin to wrinkle, so water won't stick to them," said Lagoudas.

After calculating that this approach would work, his team tested designs for an "active skin" that shifts to the shape of an ideal surface wave.

One design uses "legs" just beneath the skin that lengthen under the influence of an electric field, bending the skin upwards.

By controlling the field around each piezoceramic leg, Lagoudas' team can deform the skin into corrugations of right wavelength and amplitude to cut down drag. The corrugations can be at most 30 micrometres high.

"We measured flow velocities very close to the skin and derived the skin friction drag - we have seen reductions as much as 50%," said researcher Othon Rediniotis.

According to Lagoudas, the shape-shifting skin approach would work best as cladding for submarines.

He also said that the skin would be feasible to use this on aircraft, but that it would be more challenging. "The velocities are higher and so the traveling waves must be higher in frequency," he added.

"It's a novel technique that has been demonstrated to work under lab conditions," said Jonathan Morrison at Imperial College London, UK.

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