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Using blizzard snowfall to measure wind turbine airflow


June 25, 2014 – Claiming it as a “first-of-its-kind” study, researchers at the University of Minnesota (UMN) used snowfall during a blizzard to gain insights into the airflow around large wind turbines, with the aim of improving wind energy efficiency, especially in wind farms where airflows from many large wind turbines interact with each other.

According to researchers, The U.S. Department of Energy estimates energy losses in wind farms to be as high as 10-20%, and identifies complex airflows created by the turbines as the major culprit for such losses. As wind turbines have grown to more than 100-metres tall, field research in real-world settings has become more difficult.

“In the lab we use tracer particles to measure airflows of wind turbine models in wind tunnels, but our research was extremely constrained by an inability to measure flows at the large scale,” said Jiarong Hong, a UMN mechanical engineering assistant professor and lead researcher on the study.

Hong, who grew up in southwest China and received his Ph.D. at Johns Hopkins University, had only seen snow a few times in his life before moving to Minnesota in 2012. He wondered whether snow might be the solution to their dilemma.

“We have everything we needed in Minnesota for this research,” Hong said. “We have a fully equipped large research wind turbine at the U.S. Department of Energy-funded Eolos Wind Energy Research Center run by the University. We also have snow to serve as the particulates to measure the airflows, and committed researchers and engineers to carry out such an unprecedented effort.”

After a number of previous attempts when the snow was poor quality or the instruments malfunctioned in the cold weather, researchers headed to the Eolos 2.5kW wind turbine in Rosemount, Minn., in the early morning hours of a snowstorm on February 22, 2013.

They braved the harsh conditions in the middle of the night to set up a large searchlight with specially designed reflecting optics to generate a gigantic light sheet next to the 130-m tall wind turbine for illuminating the snow particles in a 36 x 36-m high area. The snow is easier to see in the light at night, much like the average person looks into a streetlight to see how much it is snowing during a snowstorm. Researchers videotaped the snow particles as the wind turbine spun to show airflow patterns. This video was digitized and synchronized with wake flow and load data from the fully instrumented research wind turbine.

Results of the experiment showed the technique was successful in measuring the turbulence of the airflow structure around the turbine. It is a first step in showing significant differences in the patterns of airflows in the field at large scale compared to those measured in the lab, say the researchers.

“These measurements are extremely important in our efforts to improve the efficiency of wind energy that will reduce our reliance on fossil fuels,” said Fotis Sotiropoulos, co-author of the study and director of the Eolos Wind Energy Research Center. “Who would have ever thought we’d use a Minnesota blizzard to help fight global warming.”