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Vawt Darrieus questions
By thefinis, Section Wind Posted on Wed Jan 18, 2006 at 06:28:56 PM MST
Effect of wind shadow of starter Savonius on Darrieus machine and other questions

I know that on the downwind Hawts that the tower shadow caused many problems with torque pluse and stress on the blades. Does anyone know if a Savonius rotor used in the middle of a straight bladed Darrieus would do the same? For a two bladed (even numbered)turbine the shadow on the downwind blade would happen at what I think is the top of the power curve for the upwind blade and it just seems to me that it would cause a lot of stress and torque pluse. A two bladed machine will have torque pluse anyway going from parrallel to crosswind so I don't want to make it worse. I know that a three bladed turbine would dampen the pluses out but I want to build it h--l for stout so I am trying to make it with straight through support arms.
My design is for the S rotor to run at .75 TSR and the Darrieus to run at 5 TSR when up to speed. It would have sailwing airfoils set at an attack angle of 8 and a solidity of 5% with two blades. At TSR=5 it should see an apparent wind at all times but with a changing angle of attack. Here is a good website for showing apparent wind on a Darrieus http://purrfectcatshelter.org:8080/james/darrius/ (wind blowing up means up the page). Now for a fixed angle of attack shouldn't I set it at what would be best if it was a Hawt? Sandia did a lot of testing on different attack angles but I have been unable to find if they decided on a best angle for their Darrieus. Does anyone have a web address for the DOE document if Sandia came out with guide lines for angle of attack at various TSR? While I'm asking does anyone have windturbine-analysis.com pages cached as the address now takes you to a search engine.
Should a Vawt turn counterclockwise in the northern hemisphere? Does it make any measureable difference?
Sorry for all the questions but I have been lurking for sometime. Started out researching long ago during the last energy crunch. I got sidetracked when oil got cheap and plentiful with the electric companies not wanting to talk about interconnection. I am guessing that I have a year or two at best to be able to get my electric company to play ball before they suck back up into their shell. I am building the middle section of my turbine now but would love to hear your thoughts on any of my questions especially the wind shadow effect of the Savonius.
Finis

Vawt Darrieus questions | 22 comments (22 topical)

Re: Vawt Darrieus questions (3.00 / 0) (#1)
by wind4Reg on Wed Jan 18, 2006 at 02:08:46 PM MST

These guys have done just what you are suggesting:
Savonius rotor used in the middle of a straight bladed Darrieus

They have a contact link on the website, give it a try they might provide some info, who knows.

wind4Reg

Re: Vawt Darrieus questions (3.00 / 0) (#2)
by vawtman on Wed Jan 18, 2006 at 03:42:14 PM MST

why not just build one or the other?Is the sav going to be attached to the rotor of the hbar for braking?

Re: Vawt Darrieus questions (3.00 / 0) (#3)
by vawtman on Wed Jan 18, 2006 at 05:07:35 PM MST

Im sorry you did say starter sav,missed that.A good airfoil shape will iliminate the need for the sav.To control overspeed it would be an interesting idea.Im going to tinker with that.

[ Parent ]

Re: Vawt Darrieus questions (3.00 / 0) (#4)
by thefinis on Thu Jan 19, 2006 at 08:35:05 AM MST

Sorry about this being a long post but it takes awhile to explain what I am trying to build unless you have seen the drawings. My internet went down this morning early so I had lots of time to type before posting.
Tower
I am not planning on using the H design but something more like what you might build for an S rotor. I have old highline poles that are 35' and want to set two of them 5' deep in the ground 25' apart east to west as my prevailing winds are south southwest. Then bolt another pole or a piece of 4" pipe across the top probably a foot or two from the top of the poles and another cross piece ten foot down(hope to go bigger but have to see how much torque the middle section can take). It will need either one or two support posts to help hold and stabilize the middle of the lower cross piece. Then guy the end poles with at least two guywires each. In the middle of the top cross support I'll attach a hub, lugbolts down probably from a pickup truck with disk brakes. This will have the bearing for the top and one set of brakes. On the bottom cross piece in the middle I will use the front hub from a 4 wheel drive, lugbolts up which should have disk brakes and my bearings(already designed for the loads) on it. The 4 wheel drive hub has a thru stub shaft lets me come off to either a genny or speed multiplier. If this design has too much give due to the span of the top cross piece then I will go to a four poles in the ground design and X my top cross pieces.
S rotor
This tower design lets me build a turbine with support arms top and bottom with a middle shaft that is mostly S rotor. I can then attach the airfoil to the arms top and bottom. For now the middle will be barrels cut in half with a 6" overlap bolted to 3/4" thick osb circles sealed and painted. The big debate right now is if the middle section will handle the torque it has to carry from the top airfoil support arms. I can go to an all steel middle and use old preassure tanks with the top and bottom cut off and welded to steel circles. The steel circles are rather pricey but I am still looking for a reasonable source for used flat steel. This whole thing gets bolted to the hubs with lugnuts and washers thru the end plates on the S rotor which are going to have to be steel so you can ubolt the pipe in place, balance it and then weld it. This is a simplified account as blancing the turbine and attaching the hubs, arms and airfoils are some of the most critical steps.
Airfoils
The airfoils are from The Wind Power Book by Jack Park but fitted for my machine. They are made from struts and cable with a sailcloth skin. Two things made me choose them over other blades and airfoils. One is they are light weight and the other is they change shape to match the changing air flow seen by a Darrieus. They have a very good L/D ratio and do not take a high level of skill to build. They would require sailcloth replacement every 2 or 3 years. To start with I plan to put brackets on the tube spar every 3 foot aprox to help hold the cable in place and to attach guywires to, from the middle circles in the S rotor. This means that my sails will be in 3 foot sections too. This is probably overbuild but in a 40 mph wind it should be traveling 200 mph so I would really like it to stay together. I am hoping that the highline poles will act like a yard string edger and shred the cables and spars if they fail and start coming loose absorbing much of the kinetic energy. I still plan on putting it several hundred feet from anything I don't want smashed.
Notes
This design if for an aprox 10x20 HxW turbine with the top at 28-30 high and the bottom at 18-20 foot high. The size I am trying to reach would be aprox 20x20 with the bottom at 8-10 ft high and the top at 28-30 ft high(for this one it will take the 4 poles in the ground tower design). The S rotor is a structural part of the turbine and can not be dropped out when up to speed which is why I am trying to keep its TSR down to .75 It will add little to total power but shouldn't act as a load either except in an overspeed condition. For better overspeed control should I try and make the TSR for the S rotor higher say 1 TSR which would probably act as a marginal load at design speed? Does anyone have info on how much a properly loaded turbine varies from design specs? I suspect it will end up running below design speed when loaded but haven't seen much to base expections on.

Finis
Texas born and bred
[ Parent ]

Re: Vawt Darrieus questions (3.00 / 0) (#6)
by vawtman on Thu Jan 19, 2006 at 03:37:43 PM MST

Is there any way you can post some type of drawing.

[ Parent ]

Re: Vawt Darrieus questions (3.00 / 0) (#7)
by thefinis on Fri Jan 20, 2006 at 04:11:12 AM MST

I will see what I can do but no promises.
Texas born and bred
[ Parent ]

Re: Vawt Darrieus questions (3.00 / 0) (#9)
by IntegEner on Fri Jan 20, 2006 at 08:10:39 AM MST

No drawings necessary. This is a foolish project and one of the purposes of this collection of raconteurs of many nations assembled here on OtherPower.com is to point out where suggested ideas are not in keeping with reality. Similar property owner, windy locale, large vertical axis concepts have been seen before and even constructed - see http://www.energytransfercorporation.com for an example that is largely drag-based with no Darrieus features. My earlier support of this Montana (the Big Sky State) project was for its guts and gumption as a model for the world to see but it has not had any follow up to my understanding of it.

As the years go by it is finally becoming known what is going on here. The best of the verticals (I call them "verticals") such as the Darrieuses and H-Rotors can have at most only 2/3rds of the power production per square meter swept area of the horizontals (I call them "horizontals"). This comes from that dreaded word - theory. More than this, the verticals are "blessed" with the problem that their blades must fight much more parasitic drag on them while running at all points on their circuits but especially when traveling up wind, requiring unusual care in their design and something never called out for attention and addressed by even the experts at Sandia - whom I know and to whom I have mentioned my opinions on this subject. Time, though, cures all ills and some of this may become accepted dogma one day.

The verticals have their merits in other respects and God go with you if you wish to continue with one for your ranch after having read this.

Meanwhile some perfectly sound and acceptable horizontal axis turbines such as after market, refurbished 30 to 65 kw Nordtanks and 101 kw Micons and 40 kw Aeromans and even the lattice tower Windmatics are available for land owner projects like this. Good, consistent winds are helpful not just winds that come and go. Visit the IntegEner-Wind website to see the four Nordtanks installed right near the center crossroads of our town here and running to everyone's satisfaction. Again, you will be happy that this was said and I can even lend further ideas here, not just more sales propaganda.

(My own entrepreneur, remote, small battery power wind rotators may be not in the same league but they have a lot of thought behind them and appeal to official bodies with funds available.)

Anthony C.
IntegEner-Wind
Tehachapi, CA
www.integener.com

[ Parent ]

Re: Vawt Darrieus questions (3.00 / 0) (#10)
by windstuffnow on Fri Jan 20, 2006 at 11:55:23 AM MST

Sometimes, like a cup filled to the brim, we are so full of our thoughts and opinions that it becomes difficult to add thoughts and opinions of others to move forward and learn more... at times it's good to empty our cup. There truly is more ways than one to accomplish the same outcome.
.
Have Fun! Windstuff Ed
[ Parent ]

Re: Vawt Darrieus questions (3.00 / 0) (#11)
by Waterfront on Fri Jan 20, 2006 at 01:20:23 PM MST

Wow! Nicely written!
I agree. You should consider becoming a philosopher someday, I'm sure you'd be great at it!

Waterfront
[ Parent ]

Re: Vawt Darrieus questions (3.00 / 0) (#5)
by IntegEner on Thu Jan 19, 2006 at 08:51:39 AM MST

Having made and tested smaller versions of these machines (and having had some success in this limited way) I would lend this comment. It appears that a vital piece is missing in the design elements here - the high blade drag that the verticals in general see with their entire blade lengths out on the periphery of the rotor and much of the time moving upwind. Your TSRs seem optimistic in this regard. You will thank me for mentioning this. Many are satisfied with just TSRs of two or three and even these require special low drag blades (the Darrieus design is normally built with ultra thin blades saved from stresses by the troposkein shape). Otherwise your theories and the animation websites are correct.

My own small rotators seen on my website have special blades that have the ability to strongly self-start and also run at super high rotational speeds without hesitation, something I have taken much time and effort to attain. Needless to say, I am very proud of them.

With this success, when it comes to the question of running large generators with them, I can wait. I look for more from your efforts.

Anthony C.
www.integener.com

Re: Vawt Darrieus questions (3.00 / 0) (#8)
by thefinis on Fri Jan 20, 2006 at 06:49:25 AM MST

Went to your website and waded through the chapters I thought applied to Vawts and airfoil design. I will need more time to go through all the math but from your conclusions it would seem that you like my airfoil shape, recommend I set the angle of attack to 0 and lower my TSR. Arrrgggh an attack angle of 0 just seems wrong even though I can see how with the changing wind it works out to be one of the better starting points. My design TSR is right for my solidity which is 5% in fact I could add another set of 6" wide blades bumping it to 10% and still be in the solidity range for a TSR of 5. I can change solidity pretty easy with the sailwings if I find my TSR to be lower than expected. My Grandma always said that "The proof is in the pudding boy" so pencil pushing has to give way to real life trials which may or may not bear out calculations. She also said that if you follow a good recipe you should get a good product.

I do differ with you on the way to extract the most power. The upwind side has the best air speed and best air flow(lest turblent) and I think should be what the machine is set for. The downwind side only sees the wind after it has been slowed and mixed by the blades passing thru it on the upwind side and by all of the support structure, S rotor etc. This leaves a slowed turblent wind to try and extract power from. Almost everything I have ever read says to try and design for power extraction from the fastest smoothest wind as it has the most power in it V^3. Urban settings normally suffer from the same condition reduced wind speed and turblent flow, with a tall tower usually the only way to find really usable wind.

I had planned on making the angle of attack variable on my machines until I found what I thought worked best so I'll just make sure it adjusts down to 0. How thin/thick my blade is will depend on what size tubing or rod I have to use for the stresses placed upon it. I would rather use the tubing as I expect to shred a few airfoils while looking for the right mix of materials and engineering. If it is going to rain metal out of the sky then I would rather it was tubing than soild steel rod.
Texas born and bred
[ Parent ]

Re: Vawt Darrieus questions (3.00 / 0) (#12)
by vawtman on Fri Jan 20, 2006 at 06:26:46 PM MST

Anthony would you please stop bringing up your powerless decorations on posts where people are learning and testing methods to make power.Its starting to get annoying.You prabably thrive on the attention you get allthough negative for some reason.PLEASE

[ Parent ]

Re: Vawt Darrieus questions (3.00 / 0) (#13)
by TomW on Fri Jan 20, 2006 at 06:51:34 PM MST

vawtman;

Ahem, good point. Tony seems unable to distinguish between spinning free and power extraction.

I, too, believe he is just trolling for attention and maybe website hits. The waters here must be fertile. Being a completely open and free resource run by very friendly folks, I guess we have to see it continue. Sad really because I am sure it confuses folks who can't tell fact from fiction.

Cheers.

TomW

The Truth is the Truth, even if no one believes it; and a lie is a lie even if everyone believes it

[ Parent ]

Re: Vawt Darrieus questions (3.00 / 0) (#14)
by vawtman on Fri Jan 20, 2006 at 06:53:40 PM MST

Thanks Tom

[ Parent ]

Re: Vawt Darrieus questions (3.00 / 0) (#15)
by IntegEner on Fri Jan 20, 2006 at 08:49:56 PM MST

I made my points and will let this rest. Let's see if any drawings materialize. The writer of this post will be pleased with what I have offered as time unfolds. The guys up in Montana with Energy Transfer Corporation were displeased with the mediocre attention given to their project. The fact of the verticals blade swept areas needing to be 1.5 times larger than the horizontals blade swept areas for the same power production capacity needs more technical understanding and popular recognition. Thanks, though, for the replies and I don't have a care about anything but just being a good, decent guy.

Anthony C.
IntegEner-Wind
Tehachapi, CA (where we have thousands of power producing wind turbines for the utilities and even a few dozen for homeowners and businesses)
www.integener.com

[ Parent ]

Re: Vawt Darrieus questions (3.00 / 0) (#16)
by vawtman on Sat Jan 21, 2006 at 09:34:14 AM MST

Thanks Anthony.

[ Parent ]

Re: Vawt Darrieus questions (3.00 / 0) (#17)
by IntegEner on Sun Jan 22, 2006 at 06:44:20 AM MST

Fine. This does not mean anything but that the verticals need better understanding. It seems to be something waiting for the right touch. I have always been surprised at how their reputation has been scarred by earlier problems that have no impact on the basic ideas of how they work.

Anthony C.
www.integener.com

[ Parent ]

Re: Vawt Darrieus questions (3.00 / 0) (#18)
by wdyasq on Sun Jan 22, 2006 at 11:27:18 AM MST

"This does not mean anything but that the verticals need better understanding.'

Maybe we should give the laws of physics a government check, make them go to a sensitivity camp and put them in government housing. Maybe they will understand then.

Ron
Adventure is just bad planning." -- Roald Amundsen
[ Parent ]

Re: Vawt Darrieus questions (3.00 / 0) (#20)
by IntegEner on Sun Jan 22, 2006 at 02:39:27 PM MST

Even the Lift Principle itself. Add that to the pot. My "attitude" must really show. Maybe I should get on IRC about these things.

Anthony C.
www.integener.com

[ Parent ]

Re: Vawt Darrieus questions (3.00 / 0) (#21)
by IntegEner on Sun Jan 22, 2006 at 04:14:55 PM MST

Here are a few images of the small verticals that was made up as a kit. This design has been proving itself to be something worth continuing and performs substantially better than earlier attempts based on more conventional style blades approximating NACA 0018. These blades are made from 4 inch (10 cm) aluminum roof flashing sheet from local hardware stores that has a folded leading edge to a 1/4 inch diameter with some creases added lengthwise along its chord. Otherwise it is just as thin as it comes off the 50 foot long rolls that I take home. The gap between the blade pairs can be seen in the third image. Some steel sheet was added for reinforcement plate at the mountings to the rotor arms and can be seen also.

This blade design was no accident. It was arrived at in maximizing the airflow deflection that results in the blade driving force, otherwise known as "lift", and minimizing the profile drag. The string that can be seen in the corner of the photos was there to keep the rotor from starting up while the photo was taken. Startup is not a problem here and it will even start against a load. Other views I have posted show the blades running at high speeds similar to the small horizontals. It lights the LED lights from its direct coupled axial flux generator. Unlike the Savoniuses, this can be readily scaled up both in blade length and rotor arm diameter.

(Only one blade pair is fully assembled while the other three were just hung on their arms for the photo.)

No one has ever claimed that blades like this have been tried anywhere else to my knowledge. Most everyone seems to feel they don't work until they see it start up and run.

Anthony C.
www.integener.com

[ Parent ]

Re: Vawt Darrieus questions (3.00 / 0) (#19)
by thefinis on Sun Jan 22, 2006 at 11:29:06 AM MST

I didn't intend to start an argument just needed some help on tweaks while in the build stage. IntegEner has one of the best explainations of angle of attack for lift based vawts that I have run across so far. I haven't gone through all of his math to see if I agree with how he came to his conclusions on total power extraction (downwind blade output?) but it really does not matter. I already knew that my vawt wasn't going to get as good an efficiency as a large highspeed hawt. It won't cost but a fraction of the price of a compariable hawt with the same rotor sweep area or the same power output. The problem as I see it has been some folks believing that efficiency is the top dog while in reality it is cost per watt.

I have a big cheap used diesel pickup that won't go as fast or get as good of mileage as a fancy sportscar with an efficient motor of the same hp. If I hooked up a trailer load of cattle to both of them and headed for town which one do you think would make it there first and help pay off the bank note for buying it? While this may not be a great analogy it shows that efficiency for size shouldn't be the only deciding design factor. Site location, expected use of, simplicity of, cost of and safty of all play into what you want to build. If you are going to put up an expensive tower then you probably want the most size efficient unit to keep tower costs as low as possible.

I am trying to come up with something rual landowners could build for a reasonable price from materials most of them have access to. Most farmers and ranchers I know don't need an off grid electric unit except for pumping stock water and there are already lots of ways to meet that need. They don't like climbing windmill towers either and hire that done if possible so hopefully no towers. They need it sized large enough to actually make a difference in their energy costs and simple enough to work on in their shop. For a large number of users it could all go as heat production for drying grain and for heating barns etc. (this could be done off grid). It wouldn't have to meet total energy needs just offset enough energy needs when available to more than pay for the investment gamble. Offset power costs have a better return rate then sold power production even with $60 oil.

I'll stop preaching to the choir
Finis
Texas born and bred

Re: Vawt Darrieus questions (3.00 / 0) (#22)
by IntegEner on Sun Jan 22, 2006 at 08:32:45 PM MST

You are welcome to let us know what you end up with. Remember that the wind is free but it can be a hard taskmaster with limited resources.

Anthony C.
www.integener.com

[ Parent ]

Vawt Darrieus questions | 22 comments (22 topical)

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