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re: vertical windturbine question.....
28 jun 2001
dragon  wrote:

>...the cycloturbine type with cam driven blades... will out perform
>my savonius measuring 2 ft x 8 ft in the same wind.

perhaps it has more lift vs drag.

here's a quote from paul gipe's wind power book:

  darrieus rotors have also been plagued by a misperception that they're
  less efficient than conventional wind machines. this results because
  one-half of the time the blades are traveling either with the wind
  or against it. even so the blades on a darrieus turbine produce lift
  for most of their orbit around the turbine's axis. even when the blades
  are moving downwind (retreating) they see an apparent wind due to
  their own motion sufficient to create lift. only when the blades
  are parallel to the wind does lift fall to zero.

  sandia laboratories have found that under ideal conditions darrieus
  turbines can extract more than 40 percent of the power in the wind.
  in other words, their performance is similar to that of conventional
  wind turbines, not any better but certainly no worse.

as i recall, the national research council of canada also mentioned a
number like 40% (in research reports from mcgill u) which i tend to
compare with paul gipe's estimate that hawts with good airfoils can
extract about 50% of the wind power (vs the 59% betz limit.)

nick




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