Reaching for the Sky


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Wind turbines dotting the landscape may seem futuristic, but the roots of the technology are ancient. Early sailors were probably the first to exploit the power of the wind, and by around 100 A.D. a Greek mathematician and engineer named Heron devised a wind-driven wheel to power an organ in ancient Alexandria.

Soon windmills were being used across Europe, the Middle East, and Asia to process grain and to pump water. In the United States, 19th century sodbusters used wind-powered pumps to pull water from wells, helping to transform vast acres of semi-arid prairie into irrigated farmland. Today, the multi-bladed wind pump is an icon of the American heartland.

The basics of wind power haven’t changed much over the centuries. The force of the wind turns airfoils—originally sails, now blades—around a rotor, which is connected to the main shaft. The shaft then spins a generator to generate electricity.

“A wind turbine seems easy enough to build, but it’s actually very complicated,” said Paul Veers, chief engineer at the National Renewable Energy Laboratory’s National Wind Technology Center in Golden, Colo. “Engineers must integrate aerodynamics, structural dynamics, and material fatigue with gear boxes, electric generators, and other components, and connect it all to the grid.”

A lot of engineers, however, don’t have much experience with such large-scale projects. Wind turbines are the largest rotating structures in the world. The entire process—from design to installation to operation and maintenance—deals with very large components.

“Wind turbines are immense machines,” said Douglas Adams, professor of mechanical engineering at Purdue University in West Lafayette, Ind., and director of the Purdue Center for Systems Integrity. “Onshore, utility-scale wind turbines stand nearly 300 feet off the ground and have rotor diameters approaching 300 feet. It is fascinating that the operation of such immense machines depends critically on very small things—such as the lubricating layer 1-micron-thick between the gear teeth in the gear box.”

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July 2013

by ASME.org