Environmental Engineering Reference
In-Depth Information
Figure 3-20. The Sandia/DOE 17-m experimental Darrieus VAWT under test near
Albuquerque, New Mexico.
(Courtesy of Sandia National Laboratories)
achieved, and regulating power in high winds without movable aerodynamic surfaces helps
to control system costs. Sandia researchers patented an early attempt to tailor stall behavior
by
pumped spoiling
, which involves drilling lines of holes along the blade and forcing small
quantities of air into the boundary layer. While technically feasible, initial cost and main-
tenance expenses were found to be a major disadvantage of pumped spoiling. Redesigning
the blade shape proved to be much more practical.
Engineers at Sandia and at various universities have developed airfoils that can regulate
power through stall. In 1980 researchers at Ohio State University originated the concept
of
natural laminar low airfoils
, which met the two requirements of enhanced lift at low
angles of attack and regulated stall at high angles. These specially-tailored components
were irst tested on a 5-m research VAWT at Sandia, and then their improved performance
was veriied on the 17-m VAWT [Klimas and Worstell 1986]. As a result of the NRC and
Sandia airfoil development programs, peak power coeficients of today's Darrieus turbines
have reached the same level as those of modern HAWTs.
Blade Manufacturing Improvements
The irst VAWT blades were expensive because they were made of aluminum, iber-
glass, and honeycomb materials, all of which had to be carefully itted together by hand to
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