Assessment of Research Needs for Wind Turbine Rotor Materials Technology (1991) / Chapter Skim
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4 WIND TURBINE ROTOR DESIGN ISSUES
4 WIND TURBINE ROTOR DESIGN ISSUES
Pages 67-80
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From page 67... ...
That concavity effectively eliminates certain manufacturing processes, such as filament winding, from consideration for producing the outer airfoil shell. While it also forces some modification to the female mold fabrication technique, both fiberglass and wood/epoxy composites have successfully been produced in reflex shapes without significant coot penalty.
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From page 68... ...
Thin Airfoil Family FIGURE 4-2 SERI advanced wind turbine airfoils. _/ Root Region Airfoil b)
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From page 69... ...
Since the turbine rotor designer is free to sweep energy out of the flow at whatever radium provides the least rotor cost, this is an effective solution because the cost of the slight extra length is small compared to the large reduction in inboard planform area. Low wind start-up torque is reduced, which could be a limitation for some turbine designs, but the reduction of planform area also reduces storm wind loading on the turbine as a whole, so the cost trade-off at the system level may or may not be favorable depending on start-up requirements.
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From page 70... ...
approx. @ 62% Chord Edge View FIGURE 4-3 Nine-meter GRP wind turbine blade.
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From page 71... ...
Two major Danish fiberglass blade builders used a flanged root design. One variation, called the Hutter root after its originator, used thick unidirectional roving bundles wrapped around tubular bushings within the flange (Figure 4-5~.
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From page 72... ...
Both of these flanged root designs encountered considerable trouble in service (Stoddard, 19891. Partly due to quality control and manufacturing problems, and partly due to the inevitable shrinkage of polyester upon cure, the GRP flange was often not clamped well between the hub and flange plates.
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From page 73... ...
73 1 11 Microscopic ~ Relative Motion\ J / Repetitive Motion of FRP Relative to Steel Due to Cyclic Loads 11 \ / FIGURE 4-6 Flanged root design limitation due to steel/GRP st incompatibility.
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From page 74... ...
r Thick Root / End Buildup - A\ ~ ~ `,/ _ or Oversize Drilled / Hole ~\~ FIGURE 4-7b r Laminated \leneer / Blade Shell __ ~ , a\\ \~\\ Wood/epoxy blade root.
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From page 75... ...
BLADE JOINING Efficient field joining of blade sections has not yet emerged as a major issue for blade design and manufacture, because most of today's machine" are small enough that "hipping the blades in one piece is not much of a problem. However, conceptual studies have indicated potential cost and weight advantages for two bladed rotors that are essentially one continuous structural piece due to the use of a composite Flow through.
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From page 76... ...
BLADE DESIGN CONS TDERATIONS Fiberglass Blades The least-expensive structural material for fiberglass blade construction is unidirectional roving. This is a high value-added material
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From page 77... ...
Even "tressed-skin fiberglass blades often need panel stiffening in the relatively flat aft blade area, especially inboard where the span from shear web to trailing edge can be particularly large. Expanded foams are often used to provide the required panel support, due to their light weight, moderate cost, and easy formability.
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From page 78... ...
As was mentioned previously, the veneer sheets used with this construction technique constrain the acceptable blade geometries because they can accept only a very "mall level of double curvature without splitting or creating excessive resistance to the vacuum-molding forces. In this regard the problem i" much like that for molding thermoplastic sheets, which are also relatively stiff and lack the convenient ~drape.
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From page 79... ...
Whichever material system is used, long-term fatigue performance will benefit from using simple external shapes with primary load paths that are as straight as possible, particularly in the highly loaded root and root transition areas. Minor power losses due to simplification of the inboard rotor geometry can be offset by a slight increase in rotor length, resulting in a potentially lighter and lower-cot blade of equal energy capture performance and superior long-term fatigue life.
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From page 80... ...
1981. Test Evaluation of a Laminated Wood Wind Turbine Blade Concept.
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