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Fauceted Wind Turbine, Reynolds number advice please

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Dart

Active Member
Supporting Member
Joined
Apr 9, 2015
Messages
44
Location
Near Nelson B.C.
Hello to all you amazing experts and passionate amateurs! I've found this forum to be an endless font of practical hard nosed wisdom, and creative, day dreaming CAD jockies and it's been very helpful. Thanks!

In about 2010 I created a VAWT design that by my measurements, and the measurements of a hired engineer in 2012 (report is on my website), it is the worlds best VAWT in terms of swept area efficiency at Cp 0.31 (31% of the wind energy passing through it's swept area is converted to useful shaft power).

It's true that some of the NREL Labs Flo turbines reached into 40%, but that was in scales where the turbine was over 100ft tall. In sizes of around 1m diameter, the independent testing I've looked at shows peak performance at between 11% and 17% for the thin bladed Darius (eggbeater), helical (Gorlov), or straight bladed, not much difference.

It's generally understood that the maximum amount of energy collectable from the wind by a turbine is around 59%, and that very large HAWT turbines come close to that theoretical maximum. What's not generally known is that HAWT turbines of 30ft diameter or less max out at around 30%, and HAWT Turbines of less than 10ft diameter, 15-20%. This is why no large turbine manufacturer is trying to scale it's technology down, and most small HAWT manufacturers have gone out of business.

I believe that a part of this poor performance for the scaled down thin bladed turbines is that they need high Reynolds number conditions to operate effectively.

Here's a video of the largest model I made. It was never tested by a 3rd party, but my testing lead me to believe it was a bit better performance than the 1m diameter unit. You can find more video's of different size turbines on my youtube channel.



Sadly I was terrible at running a company, and the technology ended up in the hands of a group of older wealthy folks who are rich and at least somewhat intelligent, but it turns out can't get along at all. I didn't realize wealth meant yo So it's stalled, and they own the patent and until at least a couple of them kick the bucket, I don't expect any movement.

So after a lot of thinking, I combined some of the thinking from the previous design, with some new thoughts informed by testing, and created a new design (USPTO patent pending :)). While all this was going on, one issue I had with both the old and new designs is that they are large, complex, curving shapes, and quite difficult to fabricate. I saw the news that people are building Faucetmobile clones, and revisited what I could find about the design on the web. One interesting comment, I think from Barnaby Wainfan himself, when asked about flow separation on the upper surface around the skin bending points. What Barnaby seemed to say is that in the wind tunnel they reached a conclusion about the maximum brake angle that wouldn't cause separation, and their real world project seemed to prove it out. If I recall correctly, Barnaby made a comparison to the sharp transition that aileron's and rudders in some positions can take on, and pointed out that they don't cause flow separation (in normal flight conditions).

A crossover between the Faucetmobile, and my turbine, is that they both have quite low Reynolds numbers. My turbine is a single helical blade, or can be thought of as two blades, joined at the thick trailing edges. When properly loaded and driven by the wind it's outermost edge is moving at just below the speed of the wind for a tip speed ratio of between 1 and .75. So from a simplistic point of view, the blade traveling away from the wind, see's almost 0 wind speed, and the side traveling into the wind is between 1-2 wind speed. For a 1m diameter turbine, in a 20km/hr wind, can anyone suggest what a the Reynolds number would be and how to calculate it?

Here's a preview of the new faceted turbine
 
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