A VAWT idea

[hvirtane]

I think that vertical axis

wind turbines are so much

easier to make than horizontal

axis wind turbines that even

if most of them are producing

less power they are worth of

building.

After I realized that it isn't

difficult to make props for

horizontal axis wind turbines

from straight wooden boards,

I started to think that similar

constructions could be used

for some kind of Darrieus

turbines.

These are my first drafts.

The idea started to look really similar

to Gorlov turbine, but made of wood.

There could be a small Savonius

inside to help starting...

Or you could add in the center

of the blades some small

starting devices, shaped

like cups?

And here some drafts made with a computer

today.

The disks on the tips of

the blades could be made of plywood.

One of friends is installing heating systems

in his workshop... maybe it would be possible

to try making one soon.

What do you think about the idea?

Anyone has made anything like this?

-Hannu

[skravlinge]

How big are you going to make it?  It is heavy centrifugal forces on the blades, they have to be stronger than on a Hawt. The blades are stressed more by the wind than a hawt. A drag rotor in the center will help it start, but the drag from it will make the rotor slow. In a way you must disconnect the drag rotor when the speed is reached for the lift to work. The design with not straight up airfoil, can be worth testing as then just a  bit of the rotor is in "dead" position at the time.

Why not try to split the airfoils in two wings(making it a dragrotor)and let something resist so they flap together (by centrifugal force)when speed is fast to produce lift. Your drawings show a  small diameter and high rotor, It is probably better to increase the diameter and  lower the height, unless you not have any restriction on diameter, which I have. I am building a vawt which is small diameter compare to the height just to conform the permission, not because I think it is better. The rotor and sooner the whole system I estimate to be much easier and cheaper than a hawt with 2 meters rotor. I will probably be able to show you photo of a small model of the rotor I plan to build during next week.

[hvirtane]

I think that it would be

best to make first a small

model machine,

and then make the first

real machine 6 square meters,

it means 3 m tall, 2 m wide.

Your idea for the starting

system sounds good.

It might work to have

in the middle of the blades

metal plate openings

with hinges fitted

with springs?

- Hannu

[skravlinge]

I  was checking your drawings again, and you plan to twist the airfoils, if it is done, without producing unwanted drag, I think the rotor will start by itself.

[bob g]

i like the concept mainly because as i get older i don't see myself wanting or able to climb towers, even short ones!

my property has a unobstructed ridge that intersects the prevailing winds, and i ahve also thought that perhaps several of the verticals would be a better match to my plan anyway.

i have pretty good winds up there, usually over 12 mph and frequently over 20 mph, which seems to me would be good for this approach.

even if the machines only put out around 150 to 200 watts, i have room for perhaps a dozen or so of them.

how much power does an s rotor savonius put out in a 12 mph wind, made of plastic drums?

i can see myself maintaining a battery of those before i could see myself realistically climbing even a short tower, especially in the dead of winter.

i know,,, i am a wussy

bob g

[jimovonz]

I think that is a great idea and well suited to the blades I have. (helicopter blades) As I still want to go ahead with a HAWT, I think I'll go for a drive and pick up another set of blades. Can't hurt to have two turbines now can it?

[RobC]

This type of windmill generally uses a symetrical airfoil. RobC

[Ungrounded Lightning Rod]

how much power does an s rotor savonius put out in a 12 mph wind, made of plastic drums?

While it's easy to construct an S-rotor sandia machine

from cut drums, it's not that much harder to construct

the sandia design, which gets significantly more power

for a given cross-section.

An S-savonius runs in the 12-21% efficiency range,

while the Savonius design can get about 37%.  So

a sandia machine of the same size might get you more

than twice the power of an S.

The Betz limit (the most of the energy in the air you

can collect with a wind turbine) is 59%, and a HAWT with a

high TSR can approach it within a percent.  But that just

means you need a Sandia Savonius with half-again the swept

area to collect the same power.

The main advantages of a HAWT are that, for a given power, it

is smaller and lighter and that it spins faster - letting you

use a smaller genny and thus lower the size and weight further.

This makes it easier to mount on a tower, getting access to the

higher-level winds, which are both faster and less turbulent.

Since the available energy goes with the cube of the wind speed,

and the wind picks up a LOT in a few tens of feet, being on a

tower creates a BIG advantage.  But if you want to run close to

the ground to avoid tower-climbing and/or tilt-up designs, that

is not an issue.

[skravlinge]

If you put the Vawt on top of a hill you probably not need a higher tower, just so you can  come close without get into the rotor. The windspeed up the top of a hill can be 25% stronger, which double the output. As the generator is low its easy to access. A dragrotor of type Savonius is easy to build, but the speed is slow so a gear will be needed or a complicated or more high priced generator.

A Darreus type of the other hand have high speed, and is not too complicated at all, two to four airfoils on a rotating shaft. The airfoils can be done with a metalplate bended over a pipe. The airfoil shape is not so important as they say (planes flies upside down), it is the angle of  attack which is important, the AOA of a darreus goes from 0 to 90 on a blade every turn. For my project I will not triple the price of the rotor to get a very minor better figures of the theoretical output, I will see its do what I want.

[skravlinge]

Yes I saw the blades on your pictures. You can compensate the different  at the ends, by have the vawt top and bottom in different diameters. It will probably self-start then. This blades will stand  the forces on the blades very good. You can get a real fine sweptarea with a  H-rotor with this blades. As the blades seems to be on the pictures, you have at least a 1kw+ rotor in being.If I could get hands on something like that I should for sure try it.

[hvirtane]

Savonius and Darrieus turbines are in general

not much worse then HAWT machines:

A chart of efficiency of  five different turbine types is shown in Fig.8. The efficiency or power coefficient varies with the ratio of blade tip speed to wind speed, with the peak value being the number quoted for a comparison of turbines. This will be discussed in more detail in Chapter 4. It may be noticed that the peak efficiencies of the two bladed propeller, the Darrieus, and the Savonius are all above 30 %, while the American Multiblade and the Dutch windmills peak at about 15 %. These efficiencies indicate that the American Multiblade is not competitive for generating electricity, even though it is almost ideally suited and very competitive for pumping water. The efficiency curves for the Savonius and the American Multiblade have been known for a long time [6,10 ]. Unfortunately, the labels on the two curves were accidentally interchanged in some key publication in recent years,with the result that many authors have used an erroneous set of curves in their writing. This historical accident will probably take years to correct.  (from the book: Wind Energy Systems by Dr. Gary L.Johnson, November 20, 2001)

In practice it seems to be very difficult

to get much more than 35% from any HAWT...

Yes, Darrieus turbines are in general

made with symmetrical airfoils.

- Hannu

[hvirtane]

Another way to make strong blades

for a helical Darrieus machine.

You could use metal tubes inside

as the frames of the blades.

Short airfoil sections cut

out of wood or of polyurethane,

piled on the top of each others

on the metal tubes.

- Hannu

[hvirtane]

You could use metal tubes inside

as the frames of the blades.

Short airfoil sections cut

out of wood or of polyurethane,

piled on the top of each others

on the metal tubes.

Here is a draft picture of

that design idea.

I think that you can make

Darrieus machines really

strong with this construction

method. But anyway some kind

of windbrake system is

maybe anyway needed.

- Hannu

[GeeWiz]

I ran across this up on a canadian site, it is a "Vertical Axis wind turbine". I've never seen a popular one of these, but here is a URL for your review

http://www.sustainableenergy.com/SET-wind-turbine/SET-wind-turbine.html

Their glossy .pdf

http://www.sustainableenergy.com/SET-wind-turbine/Chinook2000_VAWT.pdf

Looks interesting, but something just doesn't read right.

Gw