Morphable surfaces can increase fuel efficiency in cars

Adding golf ball-like dimples to surfaces of vehicles could reduce drag and improve their efficiency, suggests new research.

Testing over the years has proved that a golf ball's irregular surface dramatically increases the distance it travels, because it can cut the drag caused by air resistance in half.

The soccer ball being used at this year's World Cup, for one, uses a similar effect.

Now researchers at Massachusetts Institute of Technology (MIT) are aiming to harness that same effect to reduce drag on a variety of surfaces - including domes that sometimes crumple in high winds, and vehicles too.

Detailed studies of aerodynamics have shown that while a ball with a dimpled surface has half the drag of a smooth one at lower speeds, this advantage is reversed at higher speeds.

So the ideal would be a surface whose smoothness can be altered, literally, on the fly - and that's what the MIT team has developed.

"Numerous studies of wrinkling have been done on flat surfaces," said lead researcher Pedro Reis, an assistant professor of mechanical engineering at MIT in the US.

"Less is known about what happens when you curve the surface. How does that affect the whole wrinkling process," he said.

The answer, it turned out, is that at a certain degree of shrinkage, the surface can produce a dimpled pattern that's very similar to that of a golf ball - and with the same aerodynamic properties.

"We systematically tested them in a wind tunnel, and we saw a reduction in drag very similar to that of golf balls," said Reis.

Because the surface texture can be controlled by adjusting the ball's interior pressure, the degree of drag reduction can be controlled at will.

A dome that could alter its surface to reduce drag when strong winds are expected might avert such failures, Reis suggested.

Another application could be the exterior of automobiles, where the ability to adjust the texture of panels to minimise drag at different speeds could increase fuel efficiency, he said.

The study was published in the journal Advanced Materials.