New Wind Generator Being Developed

[valhalla360]

Originally Posted by Rustic Charm

Well, that's not very optomistic

It's only a matter of time until it's worked out how to get more power from less revolutions. I hope this company has actually done so.

That's very easy, just increase the gear ratio and you will get more power from less revolutions...of course the problem is you need to increase the fan size or there won't be enough power to turn the higher gears.

A more efficient approach is to keep it small and mount it higher. Higher up the wind is typically stronger and you will gain far more power from an extra few kts of wind than a more efficient fan design. If you can switch from say an 8' pole to the top of the mast, you should get more power...of course that comes with it's own set of issues.

[TrentePieds]

Rustic: Them's called Savonius turbines after the mad Finn who "invented" them. They aren't "oscillators", the are rotators. Around a vertical axis.

Right up there with the invention by nuther demented Finn ('cept this Finn was German, one Gustav Magnus): a ship driven by rotating cylinders sticking up outta the deck like like masts. As they spin, the skin friction sets the enveloping air in motion and creates a low pressure zone that sucks the ship forward.

Nothing wrong with either invention, really. As long as you are willing to sacrifice utility for novelty :-)

TrentePieds

[TrentePieds]

Quote: "I am admittedly pretty ignorant of wind generation technology. So to enable my understating of why oscillating technology does not work, could you explain to me why? I want to understand, but please remember to explain in lay person language and for average IQ."

Start with the basic tenet of geometry: The greatest possible area that you can inscribe within a perimeter of given length is that of the figure we call a circle. Every other possible figure will have a smaller area.

Take a fathom of string. lay it out in a perfect circle {yeah - I know :-)].

1: Circumference = 2 * pi * radius

in our example 6 = 2 * 3.1416 * r or r = 6/6.2832 = .955 Ft

2 Area = pi * r^2 = 3.1416 * .955^2 = 2.865 SqFt

By my contention, and that of people far cleverer than I, that is the one limiting case. Now look at a middling case:

Take your string, still a fathom long. Lay it out to describe a square. Each side would be 1.5 feet, n'est-ce pas? The area is therefore 1.5 x 1.5 = 2.25 SqFt. You can see that that area is already smaller than the circle's, though both figures have the same length of perimeter.

We'll not consider another middling case, that of the triangle, cos it involves trigonometry. If you have trigonometry at your fingertips, you prolly wouldn't have asked the question in the first place ;-)

So look at another middling case:

Take that same fathom of string and lay it out as a rectangle, with two of the sides 2 feet long. That leaves you a foot for each of the ends, n'est-ce pas?

therefore A = 2 x 1 = 2.000.

As you see, that is smaller still.

And now the clincher :-) Take the same fathom of string and lay it out as the perimeter of a rectange with two of the sides 3 ft long. What is the inscribed area?

I'll leave that to you, since you've obviously got the picture by now :-).

So you see, the ONLY worthwhile captor of wind-energy is a disk presented to the wind perpendicularly, for the amount of energy you can extract is a function of ("depends on") the cross-sectional area of the "tube" of wind blowing through the captor. That function happens to be a "second order" function, i.e. it has a term in it that needs raising to the second power. That makes it imperative that you grab every square inch of area that you possibly can.

Therefore anything other than the propeller type rotor is therefore nothing more than a risible attempt at "product differentiation" and can be safely dismissed. Aeoleus, the God of the winds, sez so :-)

Propeller design is a whole other, and quite different, argument.

May the wind be ever at your back, and always between, say, eight and two-and-twenty knots :-)

TrentePieds

[Sailor_Hutch]

I wonder if this will work any better than the eggbeater turbine that caused the homeowner's association to give the poor guy a take-down notice? Hmmm, LOL - probably not!

As far as boats go, has anyone ever seen anything other than the standard tried-and-true wind generators?

[socaldmax]

I've always been curious why fans have large "petal" shaped blades and wind generators have thin propeller shaped blades.

Since both are designed to transfer energy to or from air as efficiently as possible, wouldn't one of those be more efficient than the other? I understand that airplanes us propeller shaped blades, but they're spinning at high speeds. Wind generators are spinning at lower speeds and under more load, wouldn't a fan shaped blade, and more of them, be more efficient at capturing the wind and providing more torque, like the old windmills seemed to do?

[TrentePieds]

Quote: "...wouldn't a fan shaped blade, and more of them, be more efficient at capturing the wind and providing more torque ..."

Nope. The word "Torque" that we use in Henglish is given in German, in Danish, in Dutch and in every other sensible language by a compound noun that translates as "twisting moment". That's just what it is. A force applied on the end of a Johnston bar imparts a twisting force to the spindle or axle or nut to which the bar is applied. So you can see that torque is a function ("depends on") the length of the bar AND the "amount of push" you apply to the end of it.

It isn't torque we wish to extract from the wind, but power. Or the "push" on the end of the bar, so to speak.

All wind turbines are designed so the "tip speed" of the blades remains subsonic. Using the basic formula for the circumference of a circle you can work out in a trice what is the maximum RPM is that you can tolerate for a rotor ("wind mill") with a blade length of, say 150 ft. Give it a go :-)!

You'll see that the RPM is really low, tho the tips of the blades move at, say, 725 MPH.

Try the same calculation using a 12 INCH rotor diameter :-)

Obviously the LINEAR speed of various points along a 150 Ft blade will vary. 10 feet out from the axle it would only be 725/15 = 48MPH while the tip is still moving at 725MPH! Therefore 10 foot out the blade operates in a different aerodynamic regime than does the tip of the blade. And therefore it requires a different "airfoil" - a differently shaped cross section of the blade. A Cessna 150 has a very different "airfoil" than does an F16

Once you are down to a two-foot rotor, aerodynamics basically goes out the window, and you might as well settle for a plain ogival section, which is what ventilating fans do. The reason the prop on your boat has an ogival section is the same: The diameter is too small to benefit from greater sophistication. Besides, a cubic meter of water weighs a ton. A cubic meter of air weighs a pound and a quarter. This difference in density means that getting into "foil" design for the prop for a small boat is largely a waste of time. Law of diminishing returns :-)

In a grown-up "wind turbine" the blades can be "feathered" in order to prevent them "going supersonic" which might well destroy the turbine. They can also be locked to remain non-rotating at high wind velocities. This is normally done by a ginormous disc-brake in the gear train. The reason for doing that is that, when stationary, the "prop" only presents the actual surface of the blades to the wind. When rotating, the prop, for a number of aerodynamic reasons, presents the entire "swept area" to the wind.

As a rough rule, consider that the prop blade is only efficient in the region that lies between 35% and 90% of its length. You can intuit what that means for a short (say 2-foot) blade as opposed to a 150-foot blade.

On yachts you see "wind turbines" with a rotor diameter of something like 6 feet. This is sort of the nether limit at which it pays to do a proper prop design. But remember that even with a sooper-dooper prop, you can still only extract about 48% of the power that is contained in the six foot "tube" of wind that blows through your prop at the given wind speed. Small potatoes in my opinion :-)

TrentePieds

[Buckanear Bill]

Originally Posted by socaldmax

Those look like vertical axis wind generators to me. I've heard they are not as efficient as HAWT.

Exactly, VAWTs do not capture the wind very efficiently. This is because while 1 blade is being pushed by the wind, the opposite 1 is pushing back into the wind. A bit like backing your jib. You may still move forward, but not very fast. The advantages are that they are simpler, don't much care about turbulent wind, and can be more acceptable in populated areas. They are not good candidates for marine use, since they would need to be so much larger to capture a given amount of power.