In a winter for the record books that has plagued the Midwest with persistent subzero temperatures and walloped the Southeast with crippling ice storms, new research out of Iowa State University seems especially relevant.
Using a newly refurbished “icing research tunnel,” ISU is digging deeper into the physics behind ice buildup on airplanes and wind turbine blades with the goal of improving preparations for winter weather – not just locally but nationwide.
“When we understand the physics, we can develop better models to simulate and predict when and how ice will build up on cold days,” said Hui Hu, an ISU professor of aerospace engineering who is leading the wind tunnel research.
Iowa State’s icing wind tunnel is one of only a few like it in the nation and the only one being used for research in a university setting, Hu said. It’s been fully functional for only a few weeks following a three-year effort to renovate the 20-year-old wind tunnel, donated by the Goodrich Corporation.
It can operate at minus 20 degrees Fahrenheit with wind speeds reaching 220 mph. And it can manifest everything from frozen fog to “wet glaze ice,” according to ISU News Service.
The need for new technologies in conditions as extreme as that is evident in the recent stretch of subzero temperatures that have afflicted Iowa and the Midwest. Cedar Rapids, for example, saw low temperatures dip below zero on 14 days in January and on eight of the 13 days that have elapsed so far in February – including new record lows set Monday and Tuesday, at minus 19 and minus 21, respectively, according to the National Weather Service.
With the arctic weather that has afflicted the region of late, Hu said, some people have joked about the need for a winter-weather simulator.
“Why don’t you just open the door?” he said. “But you can’t control the temperature outside. Here, I can control everything – the wind speed, the temperature. Everything is under control.”
Ice, especially when proper preparations aren’t in place, can be dangerous and costly, Hu said. An example of that is playing out this week in the southeastern states, where Winter Storm Pax is overwhelming the region unfamiliar with extreme winter conditions.
The National Weather Service this week reported snow and “crippling” ice from Atlanta eastward, and at least 13 deaths across the South have been blamed on the weather. Hundreds of thousands of customers have gone without power due to the storm, and more than 5,800 domestic and international flights have been cancelled, according to FlightAware.com.
Deicing and anti-icing fluid is paramount to air travel in conditions like these, as ice changes the geometry and balance of airplane wings. The products are chemical mixtures of glycol and water, and without them, ice can affect an aircraft’s ability to lift and cause crashes, according to industry experts.
But relatively little research has been done on the physics behind ice buildup and all its possible effects, Hu said. The hope is that new information will lead to the development of new tools, technology and preparation techniques available to airlines in the future.
And, Hu said, the wind tunnel studies will benefit more than just air travel. It could lead to improvements for wind turbines, which dot the Iowa landscape.
Ice can reduce the efficiency of wind turbine blades, affecting – among other things – harvest productivity, according to Hu. In some cases, turbines can even fail or shutdown when ice throws off balance their spinning blades, putting extra force on their shafts and machinery.
When ice on turbine blades begins to thaw, it can be launched hundreds of yards, threatening people, structures or vehicles in the surrounding area, Hu said.
“In the past, there haven’t been many quantitative experiments to let people see the underlying physics of wing and turbine blade icing,” Hu said. “This is what’s really needed.”
The research is being funded by several grants – a $663,000 grant from NASA to study aircraft wings, a $360,000 grant from the National Science Foundation to look at wind turbine icing, and part of a $20,000 seed grant from Iowa State’s Institute for Physical Research and Technology to develop new tools to study aircraft icing.
ISU researchers – including Hu, Alric Rothmayer, a professor of aerospace engineering, Kai Zhang, doctoral student, and Rye Waldman, a post-doctoral research associate – so far have spent most of their time testing the tunnel and it effectiveness.
They have run some experiments at room temperature and are honing the refrigeration technology, Hu said.
“We want to make sure it’s working well and continuously and robustly,” he said. “We not only want to cool it down, we want it to go to any temperature we want.”
As the research progresses, experiments will analyze the thickness of ice as it flows over an aircraft wing, the heat transfer of individual water droplets as they freeze, the speed of freezing rain on a wing or blade and the patterns of ice formation.The physics research is expected to get underway next month, Hu said.