Aiming laser at model windmills shows how clean power source can stir up the atmosphere

Using smoke, laser light, model airplane propellers and a campus wind tunnel, a team led by Johns Hopkins University researchers is trying to solve the airflow mysteries that surround wind turbines, an increasingly popular source of “green” energy. The National Science Foundation recently awarded the team a three-year, $321,000 grant to support the project.

The rise in oil prices and a growing demand for energy from non-polluting sources has led to a global boom in construction of tall wind turbines that convert the power of moving air into electricity. The technology of these devices has improved dramatically in recent years, making wind energy more attractive. For example, Denmark is able to produce about 20 percent of its electric energy through wind turbines. But important questions remain: Could large wind farms, whipping up the air with massive whirling blades, alter local weather conditions? Could changing the arrangement of these turbines lead to even more efficient power production? The researchers from Johns Hopkins and Rensselaer Polytechnic Institute hope their work will help answer such questions.

“With diameters spanning up to 100 meters across, these wind turbines are the largest rotating machines ever built,” said research team leader Charles Meneveau, a turbulence expert in Johns Hopkins’ Whiting School of Engineering. “There’s been a lot of research done on wind turbine blade aerodynamics, but few people have looked at the way these machines interact with the turbulent wind conditions around them. By studying the airflow around small, scale-model windmills in the lab, we can develop computer models that tell us more about what’s happening in the atmosphere at full-size wind farms.”

To collect data for such models, Meneveau’s team is conducting experiments in a campus wind tunnel. The tunnel uses a large fan to generate a stream of air moving at about 40 mph. Before it enters the testing area, the air passes through an “active grid,” a curtain of perforated plates that rotate randomly and create turbulence so that air currents in the tunnel more closely resemble real-life wind conditions. The air currents then pass through a series of small model airplane propellers mounted atop posts, mimicking an array of full-size wind turbines.