Controversy Rages over Wind Turbine Blade Design
Two cautions precede any intelligent discussion of wind turbine blade design.
First, full command of the subject literally requires a Ph.D. in physics and math. A guy with “casual working knowledge” of wind turbine blade design probably poses as much threat as the character next to him who claims he is “kinda familiar with” plastic explosives. Complex aerodynamics, principles of lift and drag, allied principles of leverage and some stuff about torque influence wind turbine blade designs, and all intelligent discussion of blade design has a few conditions and contingencies, too: If you mount your blades vertically, you require “x”; and if you mount your blade
horizontally, then you require “y”. Both x and y show their efficiency ratings according to these graphs that challenge your command of calculus. Then, you must factor-in your allowances for Nature’s quirks and Murphy’s Law. History has shown that blade designs that add-up best on paper tend to work not at all on mountainsides; Murphy’s Wind Law states, “The better the physics, the more unreliable the machine.” In artificial intelligence, some computer functions defy “heuristic testing”: In other words, the scientists cannot explain how or why they work. They just work. The same applies in some elements of wind turbine blade design: the engineers have no explanation except “it works.”
Second, just as your mother warned you against discussions of politics and religion in polite society, so mothers should caution their children about ingenuous questions in the company of wind power experts. The naïve question, “What is the best wind turbine blade design?” may spark international incidents. World wars have erupted from less provocation. Each and every wind-power scientist and engineer has his or her favorite wind turbine blade design, and each windophile will defend his or her favorite up to and beyond death’s last gasp. If duels and gunfights remained in vogue, the winderati would contest them over questions about the best blade designs. Practical experience with wind power allows only one presumption about blade designs: the more radical and innovative the guy claims they are, the less efficiently they will work. Newbies and visionaries always fail to factor-in Murphy’s Law.
Form Follows Function in Wind Turbine Blade Design
For the sake of polite discussion and civil discourse, you may stipulate a few basic premises. Horizontal Axis Wind Turbines (HAWT’s) require their own distinctive blade designs; Vertical Axis Wind Turbines (VAWT’s) require substantially different blade designs. Invoke the aircraft analogy: you cannot use helicopter rotors where the plans call for airplane propellers. Even if the physics match-up point for point in 95% of the calculations, system failure lives in the remaining 5%. You further may stipulate that cups and scoops do not work as wind turbine blades, because they capture too much wind. Anemometers work well with their little cups precisely because they catch just what the wind delivers. Good wind turbine blades actually turn just a little faster than the wind’s speed, because they capture a little of the “apparent” wind they generate. Sailboats with “high aspect ratios” adhere to the same principle, capturing both real and apparent wind, and keeping the air moving into, through, and past the sails. Cups trap the wind; good blades keep it moving. Somehow, wind turbine blades turn faster when they “dump” just a little of the wind they catch. Those lift and drag things kick-in here. And, finally, you must stipulate that aesthetics do not count in any intelligent discussion of wind turbine blade designs. History shows that “beautiful” wind turbine blade designs perform approximately as well in the real world as Miss North Carolina would perform on “Jeopardy.” Personally we like a three blade horizontal access blade. Over time they have proved to work the best.
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