Evolution of Modern Wind Turbines Part A: 1940 to 1994 - Wind Turbine Technology: Fundamental Concepts of Wind Turbine Engineering - page 134

The 34-m diameter rotor has two step-tapered blades, each with ive sections of ex-
truded 6063-T6 aluminum. Airfoil cross-sections along the curved blade are illustrated in
Figure 3-23. The use of step-tapered blades, with a longer chord near the hubs, a smaller
chord at the equator, and a transition section in between, maintains a more uniform
Reynolds Number over most of the blade length. The high-lift, natural laminar low airfoils
used in the equatorial sections are part of a series developed speciically for use on
VAWTS. Root sections use conventional NACA airfoils , which offer superior aerodynamic
properties at lower Reynolds numbers and higher structural strength. The chord widths of
the various blade sections are too large for extrusion in one piece, so each section is made
up of either two or three extrusions with bolted lap joints in the spanwise direction, as
shown in Figure 3-23.
Figure 3-23. Airfoil cross-sections in the 34-m VAWT blades. (a) Root sections, near the
hubs (b) Transition sections (c) Center (equatorial) section [Berg et al. 1990]
Continued research work, centered on the 34-m VAWT test bed, includes validating
aerodynamic and structural-dynamic computer models, testing airfoil designs and new blade
materials, and developing various control strategies. The purpose of this work is to assist
industry to improve the VAWTs in commercial operation, as well as to develop technology
that can be used in the next generation of VAWTs.
Developing a Commercial VAWT System
Testing and modiication of the 17-m VAWT at SNL in the late 1970s rapidly
improved its performance and reliability. A low-cost, pre-commercial design was then
derived from it in 1979 under a Sandia development contract won by Alcoa Industries .
Speciications required a rotor diameter of 17 m and a power output of 100 kW, and that
the system be designed for manufacturing at low cost. By 1981 three units were installed
on sites representing speciic applications: Bushland, Texas, at the U.S. Department of
Agriculture Test Station, to demonstrate an agricultural application; Rocky Flats, Colorado,