Sandia Sizes up Wind Turbine Blade Design

By many accounts, wind energy, a relative
veteran among alternative energy sources, is well-positioned for a perfect
storm around growth: The political
climate is favorable, a downtrodden economy is hungry for economical and
efficient fossil fuel alternatives and more than 30 years of research and
development has been poured into wind energy innovations. Yet one of the
remaining barriers to widespread adoption of wind energy is honing that right
mix of functionality for a wind turbine blade design that is large enough to
support higher performance while retaining a form factor that is economical,
reliable and can be produced on a grander scale.

Sandia
National Labs
, and in particular, the Wind Energy Technologies
Dept., finds itself at the epicenter of that design challenge. The group
partners with universities and industry to conduct applied research in the area
of wind turbines and blades to increase the viability of wind technology. Researchers
at the lab are working on advancing knowledge around the areas of materials,
structural dynamics, active-flow aerodynamic control and sensors along with
pursuing innovations in the manufacturing processes and embedded
controls associated with wind blade design.

Sandia Sizes up Wind Turbine Blade Design

"We're about developing innovation
that's five years, maybe 10 years out," says Tom Ashwill, P.E., distinguished
member of technical staff at Sandia National Labs' Wind Energy Technologies
Dept. "The industry is risk-adverse to innovation - they can only look two to
three years out. We look to take risk off the table for them and try things we
don't know will work." The Sandia lab makes the results of its innovation
efforts available to industry via reports, partnerships and through regular conferences
and workshops.

Large-Scale Blade Design

One of the department's primary areas
of focus is innovation related to increasing the size of wind turbine blades.
In the early 1980s, wind turbines averaged 100 kW, but the current average
capacity is around 2 MW - a factor of 15 to 20 times more performance than what
existed 25 years ago, Ashwill explains. As demand for performance increases, so
does blade size, since blade length has a direct correlation to the increased
power generating capacity of a turbine. As far as economics go, the thinking is
that fewer, higher-capacity wind turbines are more efficient and cost-effective
than creating the infrastructure to support many smaller turbines, Ashwill
says.

Click here to read the sidebar "Developing Composite Wind Blades That Will Stand the Test of Time"

Current utility-scale turbines are equipped with blades that
range from 40m (130 ft) to 90m (300 ft) in diameter. Sandia has a research
project underway to advance that capacity to a 100m blade, which in a
traditional three-bladed turbine design, would encompass a footprint in the
order of two-and-a-half football fields in
size. This massive blade design, aimed at turbines that would reside 15 miles
offshore, creates significant design challenges around weight, structural
integrity and manufacturability.

"As they get larger, the weight of
these blades becomes an issue," says Craig Collier, president of Collier Research
Corp.
, the maker of software used to
optimize composite materials and structural sizing that came out of work done at NASA Langley
Research Center and now employed as
part of Sandia's research. "As they get larger, the question is: Can they
withstand their own weight without breaking? It's a big issue for the design of
new blades." In addition to structural strength, design engineering issues
associated with the larger blades encompass things like fatigue performance,
buckling stability, blade stiffness, twist limits and wing-tip deflection.

Sandia Sizes up Wind Turbine Blade Design

Click here for larger version

HyperSizer's legacy in aerospace has helped entities like
NASA and companies like Lockheed Martin, Boeing and Bombardier, trim at least
20 percent off the weight from wing structures. The software works with
out-of-the-box FEA solvers in a feedback loop to identify solutions that
minimize weight while maximizing structural integrity and manufacturability,
Collier says. The software analyzes complex composite structures by evaluating
designs in a ply-by-ply and finite element-by-element manner, helping engineers
optimize all possible variations on a composite laminate design.

While FEA will give engineers insight into internal unit
loads - for instance, how much air load goes into the skin of a blade or into
the spar cap - it does not, for example, provide analysis on overstressed
materials or if a bonded joint is going to have a failure. That's where HyperSizer
comes in, Collier explains. "HyperSizer will not only identify the problem, but
will go a step beyond and tell you what
to do to fix the problem," he says. "It has built-in intelligence to make those
recommendations."

Leveraging HyperSizer's built-in
optimization and intelligence capabilities, Sandia plans to refine its baseline
design for a 100m blade and optimize parts of the design to reduce weight. The software will be key in exploring how and
when to add material variants such as carbon fiber, how to address active or
passive load controls, and for experimenting with different air foils as part
of the ongoing research effort. Ashwill says he expects industry to release
wind turbines based on this blade research about seven to eight years in the
future.

"We're just looking to apply innovation to larger blade
design as we have in the past for smaller blades," Ashwill says. "HyperSizer will show us how to optimize
those designs."

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