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Formula Devised to Better Place Wind Farm Turbines

Wind Turbine Rotor (NREL)

(National Renewable Energy Lab)

Engineers in the U.S. and Belgium have developed a formula to help wind farm planners arrange the most effective placement of wind energy turbines. Charles Meneveau of Johns Hopkins University in Baltimore, Maryland and Johan Meyers at Katholieke Universiteit Leuven in Belgium presented their findings at a recent meeting of the American Physical Society’s Division of Fluid Dynamics.

The newest wind farms, located on land or off shore, typically use turbines with rotor diameters of about 300 feet. Turbines on these large wind farms are now spaced about seven rotor diameters apart. The new spacing model suggests that placing the wind turbines 15 rotor diameters apart — more than twice as far apart as in the current layouts — results in more cost-efficient power generation.

Earlier large wind farm layouts were based on simply adding up what happens in the wakes of single wind turbines, Meneveau says. The new spacing model accounts for interaction of arrays of turbines with the entire atmospheric wind flow.

According to the authors, the energy generated in a large wind farm has less to do with horizontal winds and is more dependent on the strong winds that the turbulence created by the tall turbines pulls down from higher up in the atmosphere. Using data from computer simulations and wind tunnel experiments, Meneveau and Meyer determined that in the correct spacing, the turbines alter the landscape in a way that creates turbulence, which stirs the air and helps draw more powerful kinetic energy from higher altitudes.

The engineers conducted their experiments in the Johns Hopkins University wind tunnel, which uses a large fan to generate a stream of air. Before it enters the testing area, the air passes through a curtain of perforated plates that rotate randomly and create turbulence so that the air moving through the tunnel more closely resembles real-life wind conditions.

Air currents in the tunnel pass through a series of small three-bladed model wind turbines mounted atop posts, mimicking an array of full-size wind turbines. The team collected data from the interaction of the air currents and the model turbines by using a measurement technique called stereo particle-image-velocimetry, which requires a pair of high-resolution digital cameras, smoke and laser pulses.

The research is important because large wind farms, with up to thousands of turbines, are planned or already operating in the United States, Europe and China. “The early experience is that they are producing less power than expected,” Meneveau says. “Some of these projects are underperforming.”

Read more: Laser Measurement Device Deployed for Europe Wind R&D

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