Will Brooke 3/20/2009 7:21:16 PM
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your points about turbulence are great; turbulent flow carries less energy, obstructions (like buildings or trees or mountains) tend to create a "cone-like" shadow of turbulence ~1.5 times the height of the object and for a distance of between 4 and 7 times the obstructions height (depending (mostly) on wind velocity)...
while VAWT's _CAN_ be used in turbulent flow, that is not their ideal environment. laminar flow has more extractable energy. placing a VAWT up high, in unobstructed laminar flow area, will provide it with the same potential energy as a HAWT in the same environment. while traditional vawts that we normally think of, are often seen operating at ground level, that is far from the only design, or the only implementation method.
while VAWT's _CAN_ be used in turbulent flow, that is not their ideal environment. laminar flow has more extractable energy. placing a VAWT up high, in unobstructed laminar flow area, will provide it with the same potential energy as a HAWT in the same environment. while traditional vawts that we normally think of, are often seen operating at ground level, that is far from the only design, or the only implementation method.
VAWTs are useful (but again, not ideal) because they CAN be used in turbulent flow areas. if you do not have the capacity, or ability to build a tower, or access laminar flow, then a turbulent-flow restricted, ground-level VAWT is a reasonable alternative.
statements like "they are less efficient or reliable than hawt's"... this is based on what? which VAWT design? what type of mounting and flow environment. Were they placed in areas where HAWT's were completely impractical? likely, are those ideal situations. no. do they work, even at less than peak efficiency? yes. so what is the problem?
this article, while perhaps well intentioned, appears to be poorly researched and presented. At the very least, please provide a list of references. even better - admit that you are comparing apples and oranges (and please acknowledge all the different varieties in each family, they have their appropriate applications. VAWT's would be completely impractical in the locations off scotland where the large UK windfarms exist, that is a great location and area for mega-HAWT's)
Read more: http://www.motherearthnews.com/Energy-Matters/Vertical-Axis-Wind-Turbines-Comparison.aspx#ixzz27ykQrXAa
http://www.motherearthnews.com/Energy-Matters/Vertical-Axis-Wind-Turbines-Comparison.aspx
Will Brooke 3/20/2009 7:19:49 PM
THERE IS NO SUCH THING AS CENTRIFUGAL FORCE. Ask any engineer.
(what you 'feel' when you go around a sharp corner in a car (as an example) is the centrepital acceleration of the car pushing against you. The centrepital acceleration vector is aimed at the center of the circle/curve; you (the occupant) are still undergoing linear acceleartion in the direction you were last traveling (straight ahead) until the door started exerting its force on you. So the force isnt you pushing against the door (outward), it is the door pushing against you (inward)
The same is true in a wind turbine, VAWT or HAWT. BOTH systems undergo the SAME forces. The force differences are dependent upon the total area of the wings (blades). While the traditional savoinus (egbeater) blades have very large diameter in the center, that is not the only design of VAWT available or proven. (and again, the magic of math shows us that as the radius of the blades decreas, towards the top or bottom of an eggbeater vawt, the forces they undergo correspondingly drop.
next, your complaint about wings twisting and bending -- again, the forces undergone by a blade in EITHER system are calculable and can (and should) be properly designed for. the forces in BOTH systems are similar. so do NOT assume that "HAWT's have less stresses upon them" that is simply false.
next, your complaint about wings twisting and bending -- again, the forces undergone by a blade in EITHER system are calculable and can (and should) be properly designed for. the forces in BOTH systems are similar. so do NOT assume that "HAWT's have less stresses upon them" that is simply false.
Further, ther terms of reference for statements like "more energy for a given area" is not clearly defined and in general, is misleading. Again, this is generally compared using traditional eggbeater VAWt's with guy wire supports, and the wasted space from guy wires count against the footprint. A high aspect-ratio micro-VAWT extracts a lot of energy for its footprint, can easily be mounted (as all wind turbines should be) on a tower to sit in a stream of laminar flow. A mega-HAWT with a 500' wingspan needs pi*250'^2 area to operate (so that it can turn into any direction of wind)
your points
Read more: http://www.motherearthnews.com/Energy-Matters/Vertical-Axis-Wind-Turbines-Comparison.aspx#ixzz27ylfzf8I
