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Post InfoTOPIC: VAWT Airfoil profile recommendations and Tip Speed Ration Predictions
Caleb



Senior Member

Posts: 473
Date: March 19th
VAWT Airfoil profile recommendations and Tip Speed Ration Predictions

sjh7132 wrote:

 

I think solidity is just the percentage of the swept area that's covered by blade at any instant.   So the number can range from 0 to 1 (or 0 to 100%).

 


I know that that definition makes the most sense, and yet there are variations in some research papers.  For instance:

http://www.oita-ct.ac.jp/kikai/toshimitsu/kazu/paper/PDF/OMAE2009-80081.pdf


EXPERIMENTAL STUDY OF A STRAIGHT-BLADED VERTICAL AXIS WIND TURBINE WITH A DIRECTED GUIDE VANE ROW

. . .

solidity of rotor = CZr/(2R)


The expression for solidity shows up on page 4.  C is the chord length, Zr is the number of rotor blades, R is the radius of the turbine.

That is why I asked the question.  I like your definition the best.

 



-- Edited by Caleb on Friday 19th of March 2010 04:52:18 PM

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- Bryan

Mechanical Engineer turned stay-at-home dad.
sjh7132



Guru

Posts: 1252
Date: March 19th
RE: VAWT Airfoil profile recommendations and Tip Speed Ration Predictions

Caleb wrote:

Just so I am clear on this, do you calculate solidity by:

(number of blades x chord of blade)/(PI * diameter)

I seem to recall some who have just divided by the diameter or PI * radius so you get a maximum solidity of either 2 or 2 * PI.


I think solidity is just the percentage of the swept area that's covered by blade at any instant.   So the number can range from 0 to 1 (or 0 to 100%).

 



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Steve
vawtman



Senior Member

Posts: 251
Date: March 18th
RE: VAWT Airfoil profile recommendations and Tip Speed Ration Predictions

(number of blades x chord of blade)/(PI * diameter

 Yep

 I think .3 is a good number for lift types from my trials.

V......



Caleb



Senior Member

Posts: 473
Date: March 18th
RE: VAWT Airfoil profile recommendations and Tip Speed Ration Predictions

Just so I am clear on this, do you calculate solidity by:

(number of blades x chord of blade)/(PI * diameter)

I seem to recall some who have just divided by the diameter or PI * radius so you get a maximum solidity of either 2 or 2 * PI.


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- Bryan

Mechanical Engineer turned stay-at-home dad.
helixfelix
Member

Posts: 4
Date: March 18th
RE: VAWT Airfoil profile recommendations and Tip Speed Ration Predictions

Thanks for the spreadsheet, Steve. Your link is broken because it prepends vawts.net onto your site. I'd fix it and repost but I don't want to be presumptuous.

sjh7132



Guru

Posts: 1252
Date: Feb 18, 2010
RE: VAWT Airfoil profile recommendations and Tip Speed Ration Predictions

davef_dci wrote:

Does anyone have any recommendations for the best solidity for a three bladed VAWT????   I am not certain I understand the tradeoffs with solidity and would apprecaite any advice.

With the slow moving VAWTs like the lenz, I believe a solidity of 0.33 works well.  But my gut feeling (and that's all it is) for the faster moving types is a lower solidity would be better since the blade covers more territory in less time.

I've found even with the lenz you can lower the solidity by 30% and have no effect on efficiency.

 



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Steve
davef_dci
Member

Posts: 5
Date: Feb 18, 2010
RE: VAWT Airfoil profile recommendations and Tip Speed Ration Predictions

This "Alpha" prototype was just a start.  I am working on a next generation where the generator will be in the middle of the blades.  there are two sets of three blades proposed above and below the generator to increase the likelyhood of self-starting and reduce torque pulsations.




Does anyone have any recommendations for the best solidity for a three bladed VAWT????   I am not certain I understand the tradeoffs with solidity and would apprecaite any advice.

Cheers,

Dave



electrondady1



Senior Member

Posts: 430
Date: Feb 8, 2010
RE: VAWT Airfoil profile recommendations and Tip Speed Ration Predictions

ah,dave,
you need to  double  your safety budget and get your assistant a hardhat !

it would be nice to see the alternator on the bottom where the wires are less troublesome.


Bernd
Senior Member

Posts: 233
Date: Feb 8, 2010
RE: VAWT Airfoil profile recommendations and Tip Speed Ration Predictions

Hello Dave, your turbine is looking really nice.
What kind of material you use to build the blades ?

Bernd

sjh7132



Guru

Posts: 1252
Date: Feb 8, 2010
RE: VAWT Airfoil profile recommendations and Tip Speed Ration Predictions

Dave you are too quick.  I just posted version 3 (under the same link).  There was a typo in the instructions.

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Steve
davef_dci
Member

Posts: 5
Date: Feb 8, 2010
RE: VAWT Airfoil profile recommendations and Tip Speed Ration Predictions

Steve,

Thanks for the spreadsheet.  I took a brief look and I think I understand what you're trying to do.  I'll give it a shot!

Cheers,

Dave

sjh7132



Guru

Posts: 1252
Date: Feb 8, 2010
VAWT Airfoil profile recommendations and Tip Speed Ration Predictions

davef_dci wrote:

Does anyone have a reasonable reference which can explain the pros and cons of various NACA airfoil profiles???

I have been playing around with building a small VAWT for a while and so far everything I'm doing is based on a NACA63-4-021.  I found this particular foil profile referenced on a web site someplace but wasn't able to verify that it makes sense.

In particular I am interested in any reasonable way to predict "tip speed" ratio for a given profile.  Does anyone have any suggestions?

The question is more complicated than just tip speed ratio.  Really you want to know what power you get from different tip speed ratios.  (The max tip speed ratio
is where the power is zero.)

You can pick a wind speed and TSR and calculate your angle of attack for various positions around the rotation.   Then use javafoil to get the lift, figure out how much of that lift vector is in the forward direction and use that to calculate power.

You can try my spreadsheet if you like.  It lets you copy and paste javafoil data into part of it, then enter alternator data and it iteratively solves for the operating point based on the alt and wings.  It doesn't take into account drag of a support structure.

WARNING - THIS SPREAD SHEET HAS HAD VERY LITTLE TESTING!  If you can make real world measurements and let me know if the spread sheet is even close that would be very helpful.   Also beware that java foil expects to have more classic airfoils, nothing really thick.

That said, the spread sheet is here.

This spread sheet seems to show that it is either impossible or very difficult to have a lift type vawt drive an alternator that goes directly into a battery.  It works at some wind speeds, but at others the alt stalls the turbine.   I think with a lift type VAWT a peak power tracking charger is required.




-- Edited by sjh7132 on Monday 8th of February 2010 02:35:39 AM

-- Edited by sjh7132 on Monday 8th of February 2010 03:01:14 AM

__________________

Steve
davef_dci
Member

Posts: 5
Date: Feb 8, 2010
VAWT Airfoil profile recommendations and Tip Speed Ration Predictions

Does anyone have a reasonable reference which can explain the pros and cons of various NACA airfoil profiles???

I have been playing around with building a small VAWT for a while and so far everything I'm doing is based on a NACA63-4-021.  I found this particular foil profile referenced on a web site someplace but wasn't able to verify that it makes sense.

In particular I am interested in any reasonable way to predict "tip speed" ratio for a given profile.  Does anyone have any suggestions? 

Here is a link to my Alpha prototype (along with some slow motion photography).  Goal is to get a Beta running by this summer:

http://www.youtube.com/watch?v=Ed3nPQMS6YM



Oh... and just for fun here is an animation of an interlocked helical VAWT.  Makes absolutely no engineering sense that i can think of but sure would look cool.  I might build one of these as a sculpture alone.

http://www.youtube.com/watch?v=eJUt8tPTQVU


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