Hopkins team redesigns windfarms

Hopkins researcher Charles Meneveau and his team have devised a formula to find the optimal spacing for wind turbines, an increasingly popular source of green energy. The research will help wind farm operators find the most efficient way to arrange the massive turbines.

Wind turbines function by converting the kinetic energy of wind into electricity. The appeal of wind energy increased in recent years due rising oil prices and improvements in turbine technology. However, some important questions, such as how the machines interact with the turbulent wind around them, remain unanswered.

A team led by Hopkins researchers is attempting to answer these questions through the use of small-scale windmills in the lab. Team leader and turbulence specialist Meneveau believes that studying airflow around the model windmills will allow them to develop computer models that can tell them more about the atmospheric effects at full-scale wind farms.

Meneveau’s team conducts experiments in a campus wind tunnel, which uses a fan to generate a fast-moving stream of air. Before entering the testing area, the air passes through a grid of perforated plates that randomly rotates and creates turbulence to make the air currents closely mimic actual wind conditions. The air then passes through a series of model airplane propellers mounted atop posts, mimicking an array of full-sized wind turbines.

The team uses a procedure called stereo particle-image-velocimetry to better understand how the air currents and model turbines interact. First, the researchers add tiny smoke particles to the tunnel that move with the airflow. Then a laser above the turbines emits two successive pulses of light, which enable a camera to capture the position of the particles during each flash.

This causes two dots to appear in the processed image for each particle, allowing the researchers to calculate the instantaneous velocity vector at each point and the amount of kinetic energy flowing through the tunnel.

These results could be used to develop computer models that can quantify the effects of arranging turbines in certain ways, thus avoiding the trouble of building farms without knowing what will happen. According to Meneveau, the results suggest that operators should space their turbines farther apart to increase efficiency. If the turbines are too densely packed, nearby temperature and humidity levels could be affected.

The team’s spacing mode is unique in that it takes into account the interaction of turbines with the entire atmospheric wind flow. According to Meneveau and co-author Johan Meyers, the energy generated in a wind farm depends less on horizontal winds and more on turbulence-generated winds that the turbines produce and pull down from higher in the atmosphere.

The researchers found that when spaced correctly, turbines alter the landscape in a way that generates turbulence, drawing more kinetic energy from the air above.