In a first-of-its-kind experiment, PSU researchers aim to give a powerful boost to wind energy production

Reducing the consumption of fossil fuels driving climate change requires a massive increase in clean energy production worldwide. Wind has become a significant contributor to solving the world’s clean energy problem. Wind turbines have grown significantly in stature over the past several decades, with turbine blades averaging nearly 200 feet long and towers soaring to almost 300 feet tall. These structures have reached such sizes as to come under the influence of atmospheric forces not felt closer to the ground.As a boat leaves a wake in its path as it travels over water, so, too, do wind turbines leave wakes in the air behind them. On wind farms, which often have dozens of massive turbines, the interaction of these wakes can reduce the efficiency of energy production. Mechanical & Materials Engineering Professor Raúl Bayoán Cal and first-year graduate student Natalie Frank study the turbulence created by wind turbines along with their colleague, Dr.Martín Obligado--a researcher at the University of Grenoble-Alps, France. Their work seeks to improve the tools used to design highly-efficient wind farms.

Before beginning their first term as a graduate student, Frank expressed interest in investigating a particularly challenging problem in wind farm design and turbine operation--the Coriolis force. Frank’s curiosity led to a unique opportunity for a student beginning a research career--a chance to conduct experiments at a one-of-a-kind facility at the University of Grenoble-Alps, France.

The Coriolis force is a natural atmospheric phenomenon that causes a body of mass, a hurricane, for example, to rotate perpendicular to its motion in a clockwise or counterclockwise fashion, depending on whether the object is in the Northern or Southern Hemisphere. The effects of the Coriolis force, however, aren't limited to large-scale structures like storms--they can impact turbines and the wakes they leave, reducing the efficiency of energy generation.

The University of Grenoble-Alps is home to the Laboratoire des Écoulements Géophysiques et Industriels ( LEGI ). Within LEGI is a one-of-a-kind research tool, the Coriolis platform, the world's largest turntable. The platform is 13 meters (42.6 feet) in diameter, weighs 150 tons, and rotates a full 360 degrees twice a minute. Its massive size and relatively quick rotation allow researchers to introduce the Coriolis force to experiments designed to model atmospheric and oceanic flows.

Drawing on their connections to the facility, Cal and Frank proposed a series of never before conducted experiments at the Coriolis platform, aiming to characterize the effects of the Coriolis force on the turbine wakes and operations. The novelty of the proposed project earned Frank a place at the research facility during their first term as a graduate student.

"As turbines have grown larger, they interact more with the Coriolis force," Frank said. "And that impacts the efficiency of energy production. And while there have been numerical and field studies attempting to characterize the effects of the Coriolis force on turbines, there are limitations to those approaches. Our approach was to overcome those limitations by conducting a study in the controlled laboratory setting of the Coriolis platform, and that's what we did with this project."

To conduct the study, Frank, under the direction of Cal, designed experimental protocols, built miniaturized turbines to generate data on the platform, and traveled to France to lead the experiments along with their collaborators LEGI.

According to Cal, the data collected by Frank during the experiments will help engineers understand how the Coriolis force impacts the wakes created by turbines and how to improve individual turbine operations. That, in turn, could improve models used to design wind farms and, thus, enhance the overall efficiency of wind energy.

"Small percentages changes do not sound like much," Cal said. "But when you consider these increases in efficiency across all the existing and planned wind turbines and farms globally, it adds up."

Along with others on Professor Cal's research team (the Wind Energy and Turbulence lab), Frank recently presented their findings at the American Physics Society's Division of Fluid Dynamics conference in Phoenix, Arizona.

"The Coriolis force is one piece of a much larger puzzle that is the fluid mechanics of wind energy generation," said Cal. "But it's a challenge that researchers have never tackled experimentally in a laboratory setting and with the kind of resources available at LEGI. It was a truly novel approach to solving a difficult problem."

Frank's experiments will lay the groundwork for their future studies at PSU and, in the end, form the basis for the Master's thesis.