Self-starting VAWT

[chomper]

Hi all, I've been lurking a while and reading over old posts. I'm stuck with a problem and hoping that you knowledgeable types will be able to advise me.

I'm trying to build a very small Giromill (< 3ft) mainly for fun but also to provide a few watts for lighting in the garage.

I've built a 2 bladed model with NACA 0015 airfoil section blades 150mm wide and about the same height mounted on a dual rotor arms 500mm diameter. The blades are free swivelling attached at the front and so far tried two configurations :-

1. Fixed blades with 0 degree pitch angle i.e. perpendicular to the rotor arms and this completely failed to start in all winds upto 20mph so not a great deal of use.
   
2. Free swivelling blades with stops at 0 degrees and also -90 degrees i.e. pointing outwards parallel to rotor arms, this starts readily even in light winds but only ever operates in drag mode i.e. one blade offering maximum resistance to the wind and one offering minimum. Another problem with this design was the terrible clattering impact forces of the blade banging against the stops which cause vibration and eventually broke the stop.
   
   

I'm trying to come up with a simple mechanism that allows the model to self start in low winds and then quickly acheive the hypersonic TSR > 3 in lift mode. I saw the photo's on Ed's website of his cycloturbine type design which looks complicated and I don't understand how it works but there must be simpler methods.

BTW Ed's suggestion was to use his Lenz design which is my fallback plan.

Thanks

Andrew

[Norm]

First of all go to Ed's darrius type....

then look at his pic .

http://www.windstuffnow.com/main/darrieus_type.htm

...it might be best to print out this picture and

study it....

(DSC00002)

from the bottom...the part that 2 rods are stuck

into ...that part is attached to the drive shaft

..(vertical)

Okay next round part...is an eccentric...the center hole turns freely on the drive shaft...

those rods on it, go out to the swivel part of the

vanes...the vanes swivel as they rotate.

There is an offset hole...a little shaft is fixed

firmly with setscrews. A block slips over the stub

shaft...it is fixed firmly  to the stub shaft also

...which is fixed to the tail shaft...

I didn't understand it at first either, but it is

very simple once you grasp the concept....isn't it

Ed?

                   ( :>) Norm.

[Gordy]

Andrew,

I haven built one yet. But from what I've read, going 3 bladed like Ed's lens design should help. I studied the pico design, they said their's will rock back and forth until the wind speed picks up. They solved the problem by stacking a second set of rotors on top of the first at 90 degres. So looking from the top down it would look like this + . They also mentioned the posibility of mounting a third set, with each set mounted at 120 degres.

With your free swivelling design, did you use some kind of cushion on the stops? I think rubber probably would'nt absorb enough shock. But maybe some thick foam weather striping or light springs would. Should help with the noise too.

It will be interesting to see what you come up with.

Gordy

[chomper]

I tried rubber washer stops which are too hard. If still needed I was thinking of using magnetic stops with repulsing poles which should provide a smooth cushion although it might lead to oscillation.

I'll study Ed's design but surely having a tail means the device is directional and isn't the whole point of a VAWT is that it can accept wind from any direction ? I wonder how Solway acheive self starting ?

[TomW]

chomper;

Something like a couple strips of aluminum or copper that a magnet passes thru. It would be free but no fast motion would be possible and very smooth.

Try passing a magnet very fast past or along a piece of copper or aluminum to feel the effect.

Seen this used on various scales and some roller coasters use it for non contact braking.

Cheers.

TomW

[motorhead2]

I tried all those gadgets.The giromill is hawtish and searches for wind.I think thats why Ed doesnt recommend it.I thought magnets would be the catsmeow since they would push the blades out to grab the wind.It became a hard starting Sav.A properly designed airfoil will have no problem self starting.What does your airfoil look like.

[motorhead2]

How would that help in starting.Thats what his problem is now.

[windstuffnow]

  Andrew,

    You can set the blades to 0 fixed and install a small savonius in the center.   Calculate the small machine inside to run at a TSR of around .5 when the main blades are running at or around a TSR of 3.  This way there will be little drag interference from the center when it's in operation.  The wings are actually a little large for a small machine, the darrieus likes small thin blades.  

    When the wings are allowed to swivel you'll end up with primarily a drag machine that is, for the most part, self regulating.   If the wings aren't perfectly balanced the centrifugal force will hold the wing out on the heavy side.  If their balanced at the pivot point they will folow the wind to a certain degree, if it does make it up to a TSR of over 1 you'll find it will vibrate from wing flutter.   I built one similar calling it the "free wing".   I had nothing but problems with the VAWT version, the HAWT version on the other hand worked extreemly well.  Here again, the wings were balanced.   I don't think a larger version would work as well without gearing the wings together so if one moved 1 degree they all would move the exact same degree.

     The cyclo turbine worked out quite well with quite a range of rpm depending on the amount of movement you gave it.   With some minor adjustments you could easily change it to the desired rpm you needed.  Still needs alot of work to make it a trouble free system.  That's why I recommended going with something like the Lenz turbine... keep it simple....

.

[TomW]

Duh..

He Said:



I tried rubber washer stops which are too hard. If still needed I was thinking of using magnetic stops with repulsing poles which should provide a smooth cushion although it might lead to oscillation.

Oh, why do I even bother?

[motorhead2]

Sorry Tom,I didnt read that comment before yours.My bad.Keep bothering and Merry Christmas.It got a little off topic.

[IntegEner]

Glad to see the openness about this question. Everyone seems to have a different solution to it, though. Mine is to go to doubled, fixed blades with what I have called the "pitch and offset" system. The leading edges of the doubled blades are offset from each other and the trailing edges have a pitch angle. Doubling the blades is something new and allows a wide range of possibilities of configurations to try. I am having good results with mine as can be seen on my website - www.integener.com . I can't be more specific because the detail is not easily described in words. It is good to see this interest and so keep your hopes up high.

Anthony Chessick

www.integener.com

[Norm]

I'll study Ed's design but surely having a tail means the device is directional and isn't the whole point of a VAWT is that it can accept wind from any direction ?

   No that isn't the whole point it's just one

point and just because it's got a tail doesn't

mean that it is slow and awkward to accept wind

in a different direction like a large HAWT.

[chomper]

Ed, thanks for the advice regarding the blade size, is there a standard sort of ratio of blade width (chord) to rotor arm radius and also blade height ? I'm also using a NACA 0015 profile which has a thickness of 15% of the chord length - does this seem reasonable ?

I'm guessing that 3 blades would improve starting in low winds but this does complicate the build.

On your cycloturbine design, can you explain what the tail does to the pitch and how that improves starting ? Does it contribute after starting ?

I found a great thesis here http://www.library.unsw.edu.au/~thesis/adt-NUN/public/adt-NUN20030611.092522/ that discusses pitch control systems and it seems to indicate that the ideal is for the blades to return to 0 degrees as soon as its up and running - I presume this doesn't happen with your cycloturbine.

[Stonebrain]

Hi chomper,

AFAIK Darieus-type Vawts like 'fat' aerfols,so

I think NACA 0021 would be preferable.This is because

a fat aerfoil will yield lift in a wider range of angles

of attac of the airstream.A thin aerfoil can stall when

relatif airstream have bigger angle of attac (when the direction

is closer to perpendicular to airfoil-cord.)

Allso I read It is better to have a bended cord so that

the cord fits on the circonference of your vawt.

That means that one of the first 0's of the NACA airfoilnumber is

not zero ("camber").I don't remember wich one.

With an autocad-like program you can also easily draw your

NACA00xx coordinates relatif to an bended cord-line.

The bended cordline is more important when the

cord is long relatif to the diam of your vawt.

Just some thoughts..

I didn't have much succes with my small darrieus models.

A  good darrieus seems quit tricky to me.

Savonius like or hybrids(like the Lenz) are much easier.

If you want rpm's go on,with a good air foil and some selfstarting-thig

like a small savonius in the center you should get there.

But then again,a good darrieus is dangerous.

good luck,

Stonebrain  

 

[windstuffnow]

  It's been awhile since I was involved with the Darrieus mills and I don't remember the solidity they were giving as optimum.  I had played around with them for quite a while and the only one ( true darrieus ) that I had running had small thin airfoils ( I don't recall the NACA # I used).   It also had problems starting, once in motion it was a pretty scarry machine.   After investigating them and talking with an engineer that designed some of the large units I decided not to pursue a full scale true darrieus.  They are very dangerous machines and must be checked an maintained daily.   Small models aren't to bad but you still have to check them for fatigue, it's not a matter of if it will come apart its when... you certainly don't want to be in its path when it does.  That being said, you also need to incorporate a speed control system to keep it from overspeeding in higher winds.   If it's run beyond it boundries the centrifugal forces alone will pull it apart. It only takes a quick gust to bring it to a speed where it will self destruct.   Be careful with it!  Make sure you work out the numbers before you fly it.

  I moved to the cycloturbine as an effort to control it.   The tail system worked but it did drop its efficiency depending on where you set the blade angle.   Going from one extreem to another... small angles to maintain the speed to extreem angles which basically turned it into a drag machine, it actually gave me other ideas while watching it run with different wing angles.  You can have a centrifugal driven cam to start it in drag mode, as the speed picks up the wing angles are moved back to 0 and its off an running.  They sound like a small turbo kicks in when it goes from drag to lift mode.   Here again your adding a more complex system where more things could go wrong... and trust me they will.

   I'd say build them all, carefully, learn from each of them and find the one you like best to suit your needs...

Play safe, have fun!

.

[IntegEner]

Here are a few images of the "doubled fixed blades" rotors. I like the idea so much I have even used it on horizontals rotors (I call them horizontals).





The blades are simple sheet metal bent from pieces cut from 4 inch (100 mm) wide rolls in the hardware store. They are actually quite straight and parallel but their fast motion causes this (interesting?) distortion in the digital camera. The bending is hard work and requires skill, wood dowel templates, and good C clamps, finishing with some strokes with a rubber mallet on applied padding. Since the doubled blades are nothing but thin sheet at a zero degree pitch angle with the folded (and clearly visible 20 - 30 mm offset) leading edges they speed along quite fast in even light winds.

Now here is a verticals rotor (I call them verticals) that I made using the same techniques:



It also shows the same distortion due to its surprisingly fast motion. The blades are actually quite straight and vertical. Near the bottom of the view but hard to see is a small axial flux generator that I purchased mail order as a kit from Ed Lenz of windstuffnow. (Ed, I completed it!) The blades are 22" (560 mm) long and the rotor diameter is 18" (457 mm). There are actually four blades there separated by about a one inch (25 mm) gap between them and, again, have the offset. The trailing edge of the inside blade has a pitch angle different from zero degrees, hence the name "pitch and offset system".

I could go on about this and I will maybe tomorrow with more on this thread but as everyone can see it is somewhat detailed, hopefully resulting in something that when finished runs fairly well.

What I want to say also is that thin aluminum sheet metal seems a terrible choice for wind turbine blades. The bending, though, lends the lengths some unusual strength so that it looks and performs quite adequately at even high rotation rates. I wouldn't know how to give the blade pairs their NACA profile designations except as something like "1008" and "0006" (they are different from each other), reflective of their very thin design.

Anthony "The Knuckleheaded Aluminum Sheet Metal Bender" Chessick

www.integener.com

[Aelric]

Just my two cents.  I was thinking about this same thing a little while ago.  I wonder why you couldn't use something like a pneumatic storm door closer to help regulate the blades so as it rotates into the wind the wind won't push it (centrifical force + pneumatic force) you could even play with the setting on the cylinder as I remember there is a small screw on the bottom that lets you regulate how much air can escape at once.  I would set it up so that at rest (0mph wind) it is extended out so that it has maximum surface area to catch wind then when the rotor gets started, if the wind speed picks up it furls inward with the pneumatic cylinder to act as a regulator to prevent it from flapping all about.  

[windstuffnow]

  Great job Anthony,

    The wing design reminds me of the little bi-wing planes I built and flew.  The kit was called a "hyperlight". Stits and aluminum wings, one wing section weigh'd in at around 4 lbs covered... the whole plane with motor weigh'd 240 lbs dry.   2 short stubby wings, very touchy on the stick.   You can double your lift in the same motion, although, the wings are usually shorter and skinnier.   It was fast!

    Glad to hear you got the kit together, any data from the turbine with the alternator?  

.

[SparWeb]

Chomper,

VAWT's are nifty things, and I've enjoyed working on mine this summer - learned a lot.  You've learned what everyone comes up against when building Darreius-type turbines: The torque reverses on the retreating blade when the other is going forward.  There are a lot of different things that can be done to overcome this problem, and it seems every member of this site who's tried a VAWT seems to come up with a new way.  I've even tried a few myself.

The Cycloturbine, Gyromill, and Ed's design all incorporated blade pitch changing mechanisms to allow positive torque throughout the stroke.  I think it's the most efficient manner to control a Darrieus machine's speed.  But it's not the only way!  A simple eccentrically-mounted set of arms, like Ed designed, allows self-starting.  More complex mills can go further with the control mechanisms causing the pitch-change to adjust at different RPMs to improve performance, prevent overspeeding, keep RPM constant, or simply smooth out pulses in the torque.

If you were to study the mill as it is, with blades fixed at a particular angle (say, zero degrees), what kind of RPM do you get for a given wind?  Have you figured out what TSR it's running at right now?

Your mill is of a manageable size - big enough to produce useful power, small enough to work on in a garage.