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Iowa State Aerospace Engineers hit "Gold" with a innovative dual-rotor turbine

“These are fairly mature technologies we’re talking about – a 10 to 20 percent increase is a large change”

Iowa State aerospace engineers, left to right, Anupam Sharma and Hui Hu are working to improve the performance of wind turbines and wind farms. Larger image / Photo Credit Christopher GannonIowa State aerospace engineers, left to right, Anupam Sharma and Hui Hu are working to improve the performance of wind turbines and wind farms. Larger image / Photo Credit Christopher Gannon

On a quest to constantly deliver new information to you (our followers and readers) - on wind energy technologies, projects and legislation changes, I came across two younger, hungry-looking and eager US scientists via Internet who might “just” make their mark in terms of optimizing wind turbines, and, who just might prove the viability of all future wind energy sector investments. And, yes this time around it was my favorite topic – finally a new technology in focus: The Novel Dual-Rotor Turbine for Increased Wind Energy Capture (please refer to a study identically named and with supporting content). Sounds fancy and exciting doesn’t it? Well it is! 

So to cut a long story short, the Iowa State Aerospace Engineers,  Anupam Sharma, an Iowa State assistant professor of aerospace engineering, and Hui Hu, also professor of aerospace engineering are exploring the possibility of adding a smaller, secondary rotor to wind turbines to improve efficiency and reduce wakes that is already further adding to the viability of new ideas and concepts in a future wind energy world..

Sharma and Hu studied the bases of existing turbines and discovered two major problems:

  • The base of a wind turbine is not shaped like an airfoil, moreover, it is a large, round structure that does nothing to harvest wind energy at all,
  • The large base of the blades actually disrupts the wind, causing a wake behind each, which in turn reduces the energy harvesting capacity of any downwind turbine. According to Hu, a turbine in the slipstream of another, “can lose 8 to 40 percent of its energy production, depending on conditions.”


                                                          A schematic of the proposed dual-rotor concept

So how did Sharma and Hu go about solving the problem? Simple, they added a second, smaller rotor. “To try to solve these problems, we put a small rotor on the turbine,” Hu said. “And we found that with two rotors on the same tower, you generate more energy.” Laboratory tests and computer simulations show that the extra blades increase energy generation by up to 18 percent. “These are fairly mature technologies we’re talking about – a 10 to 20 percent increase is a large number,” Sharma correctly notes:

The Iowa Energy Center awarded Hu and Sharma a one-year, $116,000 grant to launch their study of dual rotors. (The two won the energy center’s 2014 Renewable Energy Impact Award for the rotor project.) The National Science Foundation is supporting continued studies with a three-year, $330,000 grant.


The Blue Tunnel - A low speed tunnel used primarily by Dr. Hu and his research group to perform PIV (Particle Imaging Velocimetry) measurements, a technique by which a flow field can be visualized.

Using these grants experiments have and are being undertaken by Hu to study the Dual Rotor idea in the Iowa State’s Aerodynamic/Atmospheric Boundary Layer Wind and Gust Tunnel. Whilst measuring power outputs and wind loads, Hu also uses technologies such as particle image velocimetry to measure and understand the flow physics of air as it passes through and behind a rotating turbine.

All the effort is being undertaken to answer as to how, for example, is the wake distributed? Where are the whirling vortices? How could the wake be manipulated to pull down air and recharge the wind load? As you see, there are still many unanswered questions.

As a further tool being used to support their efforts, Sharma uses highly advanced computer simulations, including high-fidelity computational fluid dynamics analysis and large eddy simulations, in order to find the best aerodynamic design for a dual-rotor turbine. Where, for example, should the second rotor be located? How large should it be? What kind of airfoil should it have? Should it rotate in the same direction as the main rotor or in the opposite direction? As long as only one question of the many connected to this invention remains, then we will definitely be hearing from these two talented Scientists

Hu said Sharma’s computer modeling will drive the design of the next generation of experimental models he’ll take back to the wind tunnel. “We hope to get even better performance,” Hu said.

Well guys, carry on and you will get the improved performance you are looking for!

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