Doubled Blades

[IntegEner]

Here below is a drawing of something of an alternative configuration for designing wind turbine blades (shown as configuration B). The thought here is that despite all that has been said pro and con about doubled blades, more remains yet to be considered. Note that the blades do not resemble aircraft biplane wings so much as they do sailboat sails - the mainsail and the jib.



The input from all the aircraft aviation people in these discussions is valuable but little seems to be heard from the sailboat crowd. I think wind energy can profit from their input as well. The rigid dogma of NACA profiles has gotten out of hand, with our educational institutions giving them undue emphasis resulting in a feeling that nothing else matters or will suffice. A new wave of thought based on Newtonian Principles is making its way through the technology and answering many questions about why all the curves look as they do and how they can even be calculated with some accuracy from ordinary vector algebra.

Advantages of the second configuration include (1) potentially less parasitic drag despite the addition of a second airfoil, (2) a reduction of noise generated by such blade parasitic drag in like degree, (3) less tendency to stall, (4) greater bending strength, and (5) less use of expensive and weighty material.

Current and past thinking has always emphasized the need for a pitch angle, be it ever so small. The blades in configuration B have an attack angle but the trailing edge pitch angle is zero. The driving force comes from pressures, both positive and negative, concentrated on only the relatively small surfaces of the rounded leading edges. No mind. This works just fine. The lengthy straight "tails" are needed to generate deflection (i.e. the all-important "shoveling" from one vector direction to another) of wind flow mass passing at some distance away from the blades, from whence the greatest portion of the driving forces come.

I think even the composites manufacturing businesses viewing this would have to agree that the second configuration is more readily fabricated. The near universal use of internal cores in current blade profiles has never had a good reason from the standpoint of aerodynamics (except insofar as they help make the blade capable of sustaining bending moments) for their existence.

Anthony Chessick

IntegEner-W

Tehachapi, CA

www.integener.com

[pwr]

Anthony,

Thanks for your valuable contribution.

I've looked at your web site in the past, and like what I've read

there.  I happen to be a sailor and have sailed my homebuilt boat to

Hawaii and back to the West Coast so I know a little bit about tweaking

sail shaped to extract a little more power from the wind.  Of course I

did use some NACA data to layup my foam filled rudder, and even capped

it top and bottom to try to keep the flow over the rudder and not up

and down, bypassing it.

I'm considering building a small vertical wind generator for the boat.

In the 1980s while cruising I built a two bladed prop from NACA data

and used it on a surplus tape drive servo motor.  It was too noisy and

shook the rigging as it oscillated a little through the eye of the wind.

A vertical turbine shouldn't have the oscillation/vibration problem.

You show a bulbous leading edge on your two-blade drawing.  Do you have

any suggestions regarding that shape relative to the rest of the

blade's dimensions?   What do you suggest as an offset for the

blades?  

It seems to me that capping the two blades on top and bottom with the

cap tying the two blades together would help channel the air past the

blades plus add much to the strength of the assembly.  Any thoughts on

this?  

Thanks!

[Random Guy]

I am very curious about your posts. Do you have any experimental data at all? Can you tell where I could find information on the new wave of thought based on Newtonian Principles that is answering many questions about why curves look as they do? Can you tell me where I could look up information on parasitic drag? I would like more information on the subject so I can learn more. Thanks for your help.

[rotornuts2]

Anthony, I've looked over your website and I have to say your theories have as many holes in them as they attemp to answer,

It is extreamely common for "lift" to attributed to both bernoulli and newtonian laws of physics.

Predicting blade performance using vector algebra likely approximates reality because as I see it in the diagrams on your web site the vectors your generating approximate the lift vector described by averaging the pressure differentials on the upper and lower surfaces of the profile except your neglecting drag vector modifications.

If pressure differentials (which is how lift is described as I see it) make no nevermind then how do vortex generators substantially increase performance at extreame AoA's. I'm assuming that given your use of thin airfoils you are not willing to attribute any lift contribution to the upper surface of a wing but operate on a deflection only philosiphy.

Sails and in particular those littler sails ahead of the mainsail (I'm no sailor) act in concert the same way as slats/slots or other leading edge flaps do in an aircraft wing. It's not a new idea it's been around since the messerschmitt ME262 back in 1942-3 ish. Maybe longer but that's the oldest reference I can find.

As for doubling thin cambered profiles I've tried it. Leading edge flaps actually of various sizes and I assure you despite my grandest hopes it induced premature stall at higher rpms. Likely poor design but I don't think two full size blades riding in tandem (and looking just like a bi-plane wings complete with very early Naca profiles) will doing much better.

Speaking of induced premature stall lets talk about induced drag instead. As I understand (because I've read it all over the place)induced drag is attributed to the fact that the air flowing over a wing does not match up perfectly with the air that it parted from at the leading edge. the vortices generated as a result of the air coming together at different speeds at the trailing edge of the wing causes induced drag (drag attributed to lift). This is how I've seen it explained and it makes perfect sense and it has been modeled and visualized and computed and speculated and other ed's all over the place and no-one denies it. The flow visualizations that you see that don't show trailing edge vortecies have made some assumptions to simplify the graphic.

Trust me Anthony we're not a pack of dumbdumbs here and the guys at riso aren't a pack of dumbdumbs nor are the guys at boeing or lockhead or bombardier or saab or cessna or sandia national labs or......

The guys and gals at the airport aren't stupid either that's why when a large passenger jet comes in for a landing a procedure is in place to ensure other aircraft don't fly through the downwash that is created, yes it seems they are aware of deflected air afterall.

Mike (rotornuts signed in on another computer because his network card died and he couldn't keep his mouth shut on this one and find where he wrote down his password).

[wdyasq]

Sails and in particular those littler sails ahead of the mainsail (I'm no sailor) act in concert the same way as slats/slots or other leading edge flaps do in an aircraft wing. It's not a new idea it's been around since the messerschmitt ME262 back in 1942-3 ish. Maybe longer but that's the oldest reference I can find.

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Those little things are called 'jibs' or head sails Mike.  Don't worry, there can be so many names - 'Cutter-rig on a free standing cat-schooner with a golly-wobbler sometimes rigged as a hermaphridite brig'- it is sometimes difficult for even expurts in the field to sort the names... and boats are seldom sailed in fields.

Amoung others the DeHaviland DH82 'Tiger-Moth', UK Training aircraft used pre WWII and I think the ME/BF109(1936?) had leading edge slats complicating the airflow.

An some of do have trouble reading.  Especially if directed to a site where black letters are on dark background.  In my mid-50's I still have 20/20 eyeballs but they shout 'ouch', or at least something does, when they see crap like that.  Light on dark hutrts too, IMO.  So, when they testify to something obviously wrong, I just avoid the punishment and move on.

-------------

we're not a pack of dumbdumbs here- he couldn't keep his mouth shut on this one and find where he wrote down his password.

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I think I'll leave this one alone.........

Ron

[IntegEner]

With one of the wordiest and most explanation-filled websites within memory, I have exhausted myself in providing answers to those who want to "learn more". There is a nice booklet out there also for just $1.95 plus P&H along with a PayPal button for ordering that is recommended and may be helpful for you as well. I used to think something was wrong with me in using elementary physics to explain lift but then I found others, in the field of aviation, who have done the same within the last few years and even given it the name "Newtonian Principle", not my own invention. My experiments with the Half Square Meter rotators seen on the website have given me and many others here in Tehachapi lots of confidence. I appreciate your comments as representative of a certain contingent of experts who look down on what I have to say without looking into it. AVC, www.integener.com

[IntegEner]

I have said many times that my nickname is "Knucks the Knucklehead", sometimes "Knucks the Knerd", and with a reply like this to what I have to say on my website and in this "Rants and Opinion" section I have surely earned it, and proudly as well. Try again. AVC, www.integener.com

[IntegEner]

Don't worry, Mr. Ron, just go ahead and call me "Knucks" just like everyone else does and this will solve many of these problems arising out of communications. Throwing quotes from P.T. Barnum and A. Einstein at everyone demonstrate nothing but an elite attitude. Fix your computers to work better, if you don't mind. AVC, www.integener.com

[wdyasq]

Well, as you seem to have created new laws of physics and aerodynamics I shall start using your quotes when they become nationally known.

I doubt I have a computer problem.  And I do mind.

I honestly believe some will waste a huge amount of time and money chasing things through ignorance as I have personally done in the past taking 'expurt' advice. It is difficult enough to produce windturbines from known parts and demontrated technology.  I doubt many want to dive into questionable areas with unknown and unpublished data.

It is expensive setting up a place to live off-grid.  Monies wasted in that endevor can seldom be recovered.

And, maybe I am an elite.  I have probably built more boats, windturbines and airplanes than you have.  I have probably traveled more miles by sailboat than most on this board and sailed on more types of boats with more styles of rigs on water, land and ice.

Well - enough of this rant.

Ron

 

[finnsawyer]

So, have you built it?  That's where the proof lies.  To my mind this "Newtonian Principle" is just the flip side of the same coin, as an air stream is composed of particles having kinetic energy.  Pressure is the result of the particles bouncing off of things.  When an air flow encounters something it forms a pressure wave that then deflects and accelerates the particles.  In the case of an airfoil the deflected air moves faster over the top surface, so fewer particles hit the top surface relative to those hitting the bottom surface before they move on.  Hence, a lower pressure on the top resulting in lift.

By the way, an air foil can generate lift with a zero angle of attack (pitch angle?).  The lift goes to zero with a negative angle of attack.  It's just that one gets a greater lift coefficient with a positive angle of attack, up to about 12 degrees.

[maker of toys]

I, too, would like to read your website.

however, the 'angry fruit salad' interface and background led me to give up before I even finished the first page.  IMHO, it detracts from your message by making it look amateurish, confusing and more concerned with style than content.

Please consider using a less busy background so you don't turn off your readers before they get a chance to understand what your 'tutorial with a light touch' has to say.

-Dan

[TomW]

Sir;

Well, I have to jump on the bandwagon here, too.

Your message may be platinum and gold but the webpage layout and format make it much too hard for my aging eyes at least to read easily.

If your actual intent is to disseminate quality information then I would suggest black letters on a paper white background.

Just an opinion that seems to be shared by others.

This is attempt at constructive criticism, please accept it as such whether you take the advice or not.

Cheers.

TomW

[IntegEner]

Light touch, yes, but there is a serious side. A 33 page grant proposal went in to a state energy commission academic contractor a month ago and it will take time to take it over the hurdles but it may be worth the time for others to check back to see the progress of it on the website. This is mentioned near the bottom of the text on the "Home Links and Projects" page linked to in the Directory on the upper left of the Home page. I will do my best to make the Home page more readable with better colors and easier navigation as this may be handicapping my efforts more than I have realized. Some updates were made just this morning and more are on the way. Thanks for everyone's comments. AVC, www.integener.com

[rotornuts2]

Ron, thanks for the info on the jibs and the earlier uses of slats and I guess I fall somewhere between dumbdumb and being able to find my password.

Well, I suspect it's time to park this one and move on. Thank goodness for no more "angry fruit salad" background motifes.

Mike

[motorhead2]

Why even argue over double blades when cancelation is a factor for single blades.I built my first vawt like that last year.It spun like a sav.and was retired after 1day.

[IntegEner]

Air is heavy, two pounds per cubic yard. Think of rocks that weigh that much. The blades of a wind turbine are like the rudder of a ship that must redirect the entire ship and not just the little bit of water that passes near them. To think of only the flow at the blade surfaces and how it bounces off them or races on one side and the other to get to the trailing edge first is to miss the big picture. AVC, www.integener.com

[finnsawyer]

The rudder of a ship must turn the ship in both directions.  Hence it must have the shape of a symmetrical airfoil.  It would appear that such a shape can not exhibit lift but it does.  Acrobatic air planes use such wing profiles to allow them to fly upside down.  As soon as the attack angle is greater than zero there is lift.  Hence the ship turns or the plane flies upside down.  The ship turns because the rudder exerts a force that acts around the ship's center of mass.  In a similar fashion the tail of a plane exerts a downward force that acts around the center of gravity of the plane to counteract the rotating effect of the wings.

If you think that the flow near the surface of the airfoil is all that matters, then I think you are missing the big picture.  Mathematical solutions exist for fluid flow around a sphere and a long cylinder.  I suggest you go study them.  Your kinetic approach requires you to determine the reaction of all of the air particles with all of the surfaces and then sum (integrate) them to get the results.  As it happens Bernouli's Equation has already done that, since all we want is a macroscopic solution anyway.  

[rotornuts]

GeoM, thanks for your input on this one. I agree with you entirely. Newton and bernoulli

go together like milk and cookies when it comes to lift forces.

You know, if we're wrong it will be the biggest fluke in the history of man that the study and application of aerodynamics has made it this far.

Mike

[finnsawyer]

It is possible that the kinetic approach may allow one to more easily derive solutions to a sub class of aerodynamic problems, but I don't think it's something to become dogmatic about.  If he thinks he has a better approach, he should build it.  It's as simple as that.  But of course, "The devil is in the details".