Improving Wind Turbine Design Through Advanced Simulation Techniques

Advancements in simulation technology continue to provide benefits to engineers in the field of wind power engineering. Windpower engineers now have the ability to simulate all aspects of the wind turbine; from detailed structural models of the blades that determine stresses and strains, to highly accurate aerodynamic models of the rotor that reflect its response to the local wind field. In addition to providing detailed predictions of component/system level performance, advanced optimization software can be used to guide engineers towards more suitable solutions to their design challenges.

In this webcast, a brief overview of state of art simulations tools available from Altair Engineering will be presented. Following the introduction of the tools, two of the most influential simulation technologies will be discussed. Namely, multibody dynamics (MotionSolve) and computational fluid dynamics (AcuSolve). The webcast proceeds with a discussion of case studies that demonstrate areas in which these technologies have been successfully applied to wind power engineering.

3 Bullet Points of What Participants Can Expect to Learn:

1. Computer Simulation Technologies that will help deliver optimal wind turbine design and as a result improve turbine power output and overall operating efficiency and performance

2. State of Art Simulation Technologies for Wind Turbine Designers and Engineers

3. Reduce Time to Market and Reduce Dependency on Physical Testing

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How are wind turbine blades changing?

Rotor blades, like aircraft wings, are essentially cantilevered beams with aerodynamic exteriors. Early blades were made of wood. More recently, they consist of fiberglass and epoxy resins manufactured by reaction injection molding in rather complex equipment. The quest for greater power will demand longer blades which has led designers to examine carbon fibers as a way to take weight out and increase fatigue life.

Another recent material is a two-component epoxy that increases production of large blades thanks to a new curing agent. To assure that blade molds fill completely and fast, the epoxy reacts slowly at first. Heat applied later speeds the curing and releases the part for production of the next blade in a shorter period than previously possible. Hence, cycle times for blade manufacturing can be cut by up to 30%. Production becomes more flexible because the new resins work over a broader temperature range than conventional products.

In the wind industry, coatings are aimed mostly at blades because they are constantly moving in air and exposed to the weather. However, there are coatings for towers and bolts as well.

Pitting in blades can roughen the surfaces enough to create unstable harmonics that decrease the turbine’s efficiency, while increasing maintenance and repair costs. in steam turbines, pitting or corrosion can cause cracks in the metal. Coating wind turbine blades can prevent the damage. Manufacturers of metal coatings suitable for the wind industry say they are durable, cost-effective, and eliminate common delamination and pitting problems. The coatings spray or roll-on to ensure coverage that’s resistant to harsh weather. Manufacturers say the resins can be applied to almost any substrate. The resulting surface is said to look and wear like cast metal without the traditional expense and weight. The manufacturer says the metal coating does not conduct electricity, is non-corrosive, and can be finished, sanded, polished, brushed, machined, or given a patina just as any forged or cast metal.

Another blade surfacing material uses fluoropolymers in a film application. The manufacturer reports that its advantages include 20-year performance, longer than traditional paint and gelcoat. The chemistry and nanotechnology has been developed to meet the needs of modern wind-turbine blades and has proven longevity in demanding architectural tasks. its performance advantages include absolute UV stability, minimal dirt pickup, excellent abrasion resistance, and low reflectivity.

Trained technicians can apply the coating quickly, easily, and with little equipment. There are no sprays, solvents, or mixing so the surface quality is not at risk from human error and the working environment is far safer.

Another coating in flake and powder form, actually a high-temperature resistant thermoplastic, has a higher share of hydroxyl end groups to make it polyethersulfone compatible with high-performance epoxy resins. Composites based on such high-temperature-resistant epoxy resins usually stay brittle unless modified with heat-resistant impact modifiers. A recent powder form allows using it more easily in the resin. its use requires no solvents.

Keeping Weight Down Key to Boosting Turbine Performance

The V90-3.0 MW turbine from Vestas Americas improves on previous designs thanks to lightweight carbon fiber in  blades and stronger steel for a lighter tower. What’s more, a microprocessor controlled pitch regulator and  redesigned nacelle further improve the turbine’s performance. The company says minimizing weight was a matter of high priority.  As weight goes up, so do costs for production, materials, transportation, and installation. The payoff for the V90-3.0  MW: It takes only two to three hours for it to supply an average European family with electricity for a year. Although the  V90-3.0 MW design is not the company’s most recent design, it was a significant step forward when introduced, has  proved itself a workhorse for wind farm owners, and provided a spring board for additional designs.

The blade design is shared with the V90-2.0 MW turbine, also a 90-m rotor. The blade structure is said to differ from  previous designs by using new materials, most notably carbon fiber for the load bearing spars, and a revised blade  profile. Carbon fiber is lighter than the fiber glass it replaces and its strength and rigidity also reduce the quantity of  material needed which further reduces overall weight. Even though the V90 has a 27% larger swept area than the V80,  the new blades weigh about the same. The final blade design, in part due to a collaboration with Risø National  Laboratory in Denmark, features a plane shape and a curved back edge. The resulting airfoil improves energy  production, while making the blade profile less sensitive to dirt on the leading edge, and maintaining a favorable geometric relationship between successive airfoil thicknesses. Blade features include the microprocessor-controlled pitch regulator. OptiTip constantly adjusts the angle of the turbine blades for best position in relation to prevailing winds. This capability is used in all but one Vestas  turbine. Despite the larger rotor and generator, the V90-3.0 MW weighs less than the V80-2.0 MW turbine.

The nacelle represents a radical redesign, says the firm. Even though the 3-MW generator is larger than the unit in the  2-MW design, nacelle weights are almost equal. This was done by combining the hub bedplate directly into the  gearbox, eliminating the main shaft and thus shortening the nacelle. The result is a nacelle that can generate more  power without an appreciable increase in size, weight, or tower load. Tower improvements come from a stronger steel which requires using less of it. Towers are now constructed in fewer sections than previous designs, with significant  savings in material, transportation, and installation.

Since its introduction in 2002, the company says it has installed more than 1,000 V90 3.0 MW units around the world. The design has been a springboard for the V112-3.0 MW unit a recently introduced on and off-shore turbine. The V112,  however, will not see service in the U.S. till about 2011 and later in Canada.

Blade sensors could let turbines adapt faster

Researchers have developed a technique that lets sensors monitor forces exerted on wind turbine blades, a step toward improving their efficiency by letting them adjust to rapidly changing wind conditions. The research by engineers at Purdue University and Sandia National Laboratories is part of an effort to develop a smarter wind turbine. “The goal is to feed information from sensors into an active control system that precisely adjusts components to improve efficiency,” said Purdue doctoral student Jonathan White, who is leading the research with Douglas Adams, a professor of mechanical engineering and director of Purdue’s Center for Systems Integrity.

The system also could help improve wind-turbine reliability by providing critical real-time information to the control system to prevent catastrophic wind-turbine damage from high winds.

The team embedded uniaxial and triaxial accelerometers inside a wind turbine blade as it was built. The sensors measure acceleration in different directions, necessary information to accurately characterize a blade’s bending and twisting and small vibrations near the tip that eventually cause fatigue and possible failure.

The sensors also measure two types of acceleration. One type, dynamic acceleration, comes from gusting winds, while the other, static acceleration, results from gravity and steady background winds. It is essential to accurately measure both forms to estimate forces exerted on the blades. The blade is being tested on a research wind turbine at the U.S. Department of Agriculture lab in Bushland, Texas.

Such sensors could be instrumental in future turbine blades with “control surfaces” and simple flaps like those on an airplane’s wings to change blade aerodynamics. Because these flaps would be changed in real time to respond to changing winds, constant sensor data would be critical.

“The industry is most interested in identifying loads exerted on turbine blades and predicting fatigue, and this work is a step toward accomplishing that,” says White.

“It is useful to control the blade pitch to optimize energy capture by reducing forces on the components in the wind turbine during excessively high winds, or increase loads in low winds. This should also help improve reliability. Turbine towers can be 200 feet tall and more, making it expensive to service and repair damaged components,” says White.

The research is funded by the U.S. Department of Energy through Sandia National Laboratories. Sandia is a multiprogram laboratory operated by Sandia Corp., a Lockheed Martin Co., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.