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Vestas Scholars Turn Wind Scholarship into Windfall

Two mechanical engineering students at the University of Massachusetts Amherst have literally taken advantage of a windfall from a prominent wind power company and used it to propel their futures. Jacque Heger and Samuel Deptula each received $5,000 scholarships for the 2008-2009 academic year from Vestas Americas, the leading supplier of wind power solutions with over 35,000 wind turbines installed. As part of this Vestas Scholarship Program, they also received $8,000 apiece this summer to do wind-related research for the Wind Energy Center at UMass Amherst. Heger used her research funding for making key physical improvements to wind turbine blades, while Deptula employed his Vestas support to help reboot a wind tunnel on campus that had been abandoned for more than a decade.

Their research, done under the watchful eyes of Professors Robert Hyers and James Manwell of the Mechanical and Industrial Engineering Department, was part of the UMass Amherst Research Experience for Undergraduates. Both research projects promise to create significant progress for wind energy in general, and the Wind Energy Center in particular.

Heger’s research, done with Professor Hyers and mechanical engineering undergraduate John Gabour, involves a phenomenon known as “bend-twist coupling,” which describes the behavior of a wind turbine blade in the field under stress from wind forces.

“The blade will deflect according to the amount of aerodynamic pressure the wind applies to it,” notes Heger. “The blade will both bend against the oncoming wind and twist towards or away from it.”

Though extreme blade deformation is counterproductive, some deformation can be useful because it will slow down the rotor speed (called “passive furling”) and allow the wind turbine to operate safely in high winds that might normally cause a turbine to be shut down to avoid damage.

Heger’s research involves altering the blade geometry through a newly designed proprietary internal structure. She also looked at the shell and spar material. By creating a turbine blade that is capable of greater twist under load, the angle of attack is reduced, resulting in lower rotor velocity

Along with analyzing the twisting mechanics of the blade geometry, the researchers also revamped the blade’s material properties.

“The desired material must have high bending stiffness and low torsional stiffness,” says Heger.

Woven fiberglass and carbon fiber are typically used in industry because they are strong, durable, and lightweight. However, these materials do not provide the desired torsional flexibility. That’s why Heger and her colleagues researched new composites for the bend-twist application. 

Meanwhile, Deptula, with Professor Manwell as his advisor, was at work testing and retrofitting a low-speed wind tunnel that had been built on campus in the 1960s but had been “in mothballs” for many years. The Wind Energy Center and other research units on campus can make plenty of use out of the wind tunnel, if serviceable, by using it to conduct fluid and heat transfer experiments, instrument calibrations, and other functions. So Deptula’s job this summer was to perform modeling, analysis, and validation-of-flow-quality tests on the old wind tunnel.

“Aging equipment and the installation of a new building (Agricultural Annex B) 10 feet from the exhaust outlet of the tunnel required that flow quality within the test section be evaluated,” says Deptula. “The lack of a fan motor voltage controller also created the possibility of varying wind speeds, which would undermine the value of experimental results and calibration accuracy. It was also important to investigate how the proximity of the annex building to the exhaust of the tunnel affects velocity, pressure, and turbulence in the test section.”

To determine this last factor, the proximity of the annex to the exhaust, Deptula used CAD software to model the major features of the wind tunnel and the agricultural annex, and then he simulated the behavior of air flow exiting the wind tunnel. These plots revealed that the annex had almost no effect on the flow characteristics.

The computer simulations did not take into account many variables that could potentially alter flow characteristics.

“These included varying fan motor speed due to voltage fluctuations, air currents outside the wind tunnel laboratory as a result of natural winds, and variable weather conditions such as temperature, humidity, and barometric pressure,” comments Deptula.

To characterize these factors, Deptula began constructing an apparatus that could measure total and static pressure across the entire three-dimensional test section of the wind tunnel, while simultaneously collecting temperature, fan motor speed, and barometric pressure data.

The work of both Heger and Deptula will go a long way toward driving both of their careers in engineering.

“It’s obvious from the 2008 presidential campaign that renewable energies are going to be important in the near future,” says Heger. “Right now I’m focusing on wind. Now that I know I want to specialize in renewable energy, I get so excited every time I talk about it.” (August 2009)