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DARRIEUS BLADE AIRFOILS
By johnjach, Section Homebrewed Electricity Posted on Fri Dec 05, 2003 at 09:51:18 PM MST
What type of airfoils should be used for a Darries VAWT?

If I were to build a straight-bladed, H-rotor type Darrieus turbine, what would be the optimal number of blades and the best type of airfoil to be used if I wanted the unit to be self-starting? If the machine were to have a swept area of about 16 square feet(a 4 x 4 machine), what I've garnered from reading so far is that I would be better off with a thicker, more bulbous shape airfoil and 3-4 blades. Is this correct?
I got this idea from looking at the Solwind turbine at www.solwind.co.nz. This machine is said to self-start in low winds and the photos show the blades to be wider than most Darrieus blades.

DARRIEUS BLADE AIRFOILS | 5 comments (5 topical)

Re: DARRIEUS BLADE AIRFOILS (none / 0) (#1)
by monte350c on Fri Dec 05, 2003 at 10:07:06 PM MST

Hi Johnjach,

There is a lot of info out there about VAWT's and research into blades. I've switched to a HAWT project, but would still like to try a VAWT at some time in the future. The main problems I saw with the VAWT / H-Bar proejct I have been working on all center around centrifugal force and the complexity of dealing with an appropriate furling / protection system for the generator. Centrifugal loads get pretty spectacular when the rpms go up - and it becomes obvious pretty quickly that dealing with those potential runaway scenarios should be the main preoccupation when designing a VAWT. Having said that - I'm still hopeful about the VAWT thing. I found Dr. Gary Johnson's book particulary helpful. You can download it for free here:

http://www.eece.ksu.edu/~gjohnson/

Also if you haven't already found it there's a very good resource for VAWT's at Sandia Labs site:

http://www.sandia.gov/Renewable_Energy/wind_energy/topical.htm

If you scroll down you'll come to a section titled "VAWT archives"

There's good reading in:

"Final Project Report: High-Energy Rotor, Development, Test and Evaluation"

"Aerodynamic Characteristics of Seven Symmetrical Airfoil
Sections Through 180-Degree Angle of Attack For Use In
Aerodynamic Analysis of Vertical Axis Wind Turbines"

"Aerodynamic Performance of a 5-Metre-Diameter Darrieus
Turbine with Extruded NACA-0015 Blades"

"Free-Air Performance Tests of a 5-Metre-Diameter
Darrieus Turbine"

Good luck with you project, and keep us posted!

It is a lot of fun in any case

Ted.

Re: DARRIEUS BLADE AIRFOILS (none / 0) (#2)
by johnjach on Sat Dec 06, 2003 at 10:05:44 AM MST

Thanks Ted,

I wasn't aware of this information. I looked at the websites you mentioned are a gold mine of ideas. This will make for very interesting reading and research.

[ Parent ]

Re: DARRIEUS BLADE AIRFOILS (none / 0) (#3)
by windstuffnow on Sun Dec 07, 2003 at 08:35:38 AM MST

I've found the 3 blade unit to be the best for reliable self starting. 2 blades will sometimes "bobble" back and forth until either a gust hits it or some turbulant air forces it past the point of no return. The same will happen with a 4 blade arrangement although more reliable than simply 2.
The "fat" wing will start quicker than the thin blades but there are advantages and disadvantages to either. The fat wing has more drag ( especially on the downwind side ) and will tend to run slower than the thin aerodynamic foils but will produce power at lower wind speeds. Also, the fat wing has a better tendency to stay "in check" for overspeeding because of the extra drag. The thin blades are impressive and a bit more efficient but If you've ever built a small one, the rpm gets quite scarry fast. If you've ever noticed the standard HAWT air foil has a start up sound and when it reaches its designed TSR it sounds like a turbo kicked in... the same happens to a properly designed darrieus wing. It's hard to explain unless you've actually experienced it. As long as the wings are stalled to some degree it will spin but the output is considerably low, but once it reaches its designed TSR the whole tone of the machine changes, its making power... and it sounds like it!!!
Build one of each ( small ones to experiment with) Take note of the differences... I prefere the "fat" wing design, although not as efficient in high winds its not as scarry as the fater moving thin wing.

Have Fun!
Ed

Have Fun! Windstuff Ed

Re: DARRIEUS BLADE AIRFOILS (none / 0) (#4)
by RayW on Sun Dec 07, 2003 at 09:48:26 AM MST

Hi Ed;
Should the airfoil shape of a darrieus blade flat on one side or both sides curved??
RayW

[ Parent ]

Re: DARRIEUS BLADE AIRFOILS (none / 0) (#5)
by windstuffnow on Sun Dec 07, 2003 at 12:06:28 PM MST

The standard blade is symetrical, that is to say it has an airfoil on both sides. The "flat on one side" will work with a lesser degree of torque depending on the design. If your depending on developing power from strictly lift then the symetrical blade is what you want. If your building a combination of lift and drag there are many different variations that will work quite well. Lift and drag versions attempt to offset any upwind forces that robs power from the downwind side.
Althought there are "standard" ways to build specific machines the world is still open for unique and untried versions. There is always a better way!

Ed

Have Fun! Windstuff Ed
[ Parent ]

DARRIEUS BLADE AIRFOILS | 5 comments (5 topical)

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