News Column

ISU researchers study ice on turbines, airplanes

February 16, 2014

By Anthony Capps, Ames Tribune, Iowa



Feb. 16--Winter is the worst season for wind turbines. The build up of ice can cause costly damage, and researchers at Iowa State University are working to reduce problems caused by icing.

Hui Hu, professor of aerospace engineering at ISU, has been heading a three-year project using the university's Icing Research Tunnel to study the effects of ice on wind turbine blades.

The refurbished 20-year-old icing wind tunnel can create conditions of minus 20 degrees Fahrenheit, wind speeds up to 220 mph, frozen fog and a glaze of ice.

In the past, most models of what happened to water and ice on turbine blades had only been through a computer's aerodynamic projection. There wasn't any physical research to back it up.

Hu, who's been at Iowa State since 2004, set out to understand the physics and a summation of ice on wind turbine and airplane blades.

"We need to really know what's going on," he said. "You can use some mathematics to describe some of the theory about what it will be, but results and seeing the physics is almost impossible to see with a model based on your imagination."

The research is comprised of a $663,000 grant from NASA to study icing of aircraft wings, part of a $360,000 grant from the National Science Foundation to study icing of wind turbine blades and part of a $20,000 grant from Iowa State'sInstitute for Physical Research and Technology to develop technology to study aircraft icing.

Hu's co-workers on the projects, which uses cameras and lasers, are Alric Rothmayer, professor of aerospace engineering, Kai Zhang, a doctoral student, and Rye Waldman, a post-doctoral research associate.

President Obama's push for renewable energy brought wind power to the front. Right now, about 23 percent of Iowans receive power from wind turbines, which places Iowa as one of the top wind producers in the country.

But winter brings its share of problems.

Ice collects on the blades and it "changes the geometry of the turbine and therefore the efficiency will drop."

The efficiency that a turbine will drop might not be too much, but one propeller with more ice than the other two can put more pressure and stress on them and the turbine itself. The results can be engine failures and shut-downs.

Ice collects in two forms: rime, which forms in cold and dry conditions and creates a layer on the blades that changes the balance but doesn't affect the aerodynamics, and glaze, which forms when it's not too cold and only a portion of a droplet turns to ice so a droplet can flow a little and creates some weird patterns.

The glaze form was something Hu was really interested in learning about.

Hu believes the research is also important because it helps us start to understand what can happen on airplanes in winter weather. The water droplets can freeze and add weight to the airplane.

Hu said in parts of Europe some places have covered the blades with heaters, but up to 70 percent of the total energy produced by the turbine had to be used to de-ice.

As everything melts, the ice on the propellers does come with a risk. Hu said with ice can slide off and larger pieces can be thrown more than 3,000 feet. It does pose a danger passing vehicles, but Hu only knew of one incident.

The results Hu found weren't what was expected.

"We're all pretty excited about this," he said. "We've never seen results come back from a lab and many things we've thought aren't actually happening."

Hu hopes the research will lead to more, which is certainly needed, and ideas for engineers to develop new solutions.

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(c)2014 the Ames Tribune, Iowa

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Source: Ames Tribune (IA)


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