A technology originally developed to increase lift in aircraft wings and simplify helicopter rotors can reduce the cost of manufacturing and operating wind turbines. Circulation control aerodynamic technology would allow wind turbines to produce significantly more power than current devices at the same wind speed.
Engineers at the Georgia Institute of Technology and PAX Streamline recently embarked on a two-year project that will lead to the construction of a demonstration pneumatic wind turbine. The project is being funded by a $3 million grant from the Advanced Research Projects Agency-Energy (ARPA-E), the federal energy research and development organization.
“Our goal will be to make generation of electricity from wind turbines less expensive by eliminating the need for the complex blade shapes and mechanical control systems used in current turbines,” says Robert Englar, principal research engineer at the Georgia Tech Research Institute (GTRI). “Because these new blades would operate effectively at lower wind speeds, we could potentially open up new geographic areas to wind turbine use. Together, these advances could significantly expand the generation of electricity from wind power in the United States.”
Circulation control techniques use compressed air blown from slots on the trailing edges of wings or hollow blades to change the aerodynamic properties of those wings or blades. In aircraft, circulation control wings improve lift, allowing aircraft to fly at much lower speeds-and take off and land in much shorter distances. In helicopter rotor blades, the technique-also known as the “circulation control rotor”-simplifies the rotor and its control system, and produces more lift.
The ARPA-E project will apply the technique to controlling the aerodynamic properties of wind turbine blades, which traditionally must be made in complicated shapes and controlled by complex control mechanisms to extract optimal power from the wind.
“The speed at which these turbines would begin to operate will be much lower than with existing blades,” says Englar. “Places that previously [were] not suitable locations for wind turbines may now be useful. The blown technology should also allow safe operation at higher wind speeds and in wind gusts that would cause existing turbines to be shut down to prevent damage.”
Because they would produce more aerodynamic force, torque and power than comparable blades, Englar claims that blown structures could also allow a reduction in the size of wind turbines.
“If you need a specific amount of wind force and torque generated by the wind turbine to generate electricity, we could get that force and torque from a smaller blade area, because we’d have more powerful lifting surfaces,” Englar points out.
The new turbine blades will be developed at GTRI’s low-speed wind tunnel research facility, which is located near Atlanta. A major question that needs to be examined by engineers is how much energy will be required to produce the compressed air that blown blades need to operate.
Preliminary studies conducted by Lakshmi Sankar, a professor of aerospace engineering at Georgia Tech, indicate that wind turbines equipped with blown blades could produce 30 percent to 40 percent more power than conventional turbines at the same wind speed-even when the energy required to produce the compressed air is subtracted from the total energy production.