Blade Speed

[Dennis Damm]

Hi everyone hope my questions dont sound to dumb

OK if a gas generator runs at 3600 rpm to

produce 110 volt when load is applied more gas is

pumped in to maintain the 3600 rpm but the generator doesnt

excede the 3600 speed

now on a wind turbine with a cutin speed of lets say

100 rpm to achive 12 volts and a bridge rectifier has .7 voltage

drop across it the turbine will speed up to make 13 volts to lets say 110 rpm

and the battery starts charging 120 rpm's for 14 volt's

when the battery reachs 14 volts it's full and the load

controller comes on and applies a load then as long as the turbine can keep up the battery will not drain down and the turbine should stay at 120 rpm's?

providing i have the wind to maintain the load

so i guess the question is my turbine should never go much faster than 120 rpm's

i hope.

thanks for any help on this issue

[Flux]

If it doesn't go much faster than 120 rpm they you will have rotten performance.

If your generator is super efficient your logic is correct for the generator, it is not much good for the prop.

To extract maximum power you must make your prop speed rise in the same ratio as the wind speed ( constant tip speed ratio), unless you at least approximate to this you will stall the blades and the power extracted will not rise with wind speed.

Your dilemma is to allow the prop to track wind speed and generate increasing power into a virtually fixed voltage.

I have indirectly covered this several times recently so if you go back through the last week or so's posts you should find something about matching generator power and speed.

Flux

[nothing to lose]

That is actually not correct about the RPM of the wind gennie.

Your gas generator is set to run at 3600rpm, under a load it uses more feul than it does at no load because it has to maintain speed and make the power, which takes feul.

It's all preset, runs at one speed and produces 120V at that speed and the more amps it produces the more feul it burns.

Now a wind gennie is not like that at all. It can turn however fast the blades will turn in however much wind you have. Yes cut in may be at 100rpm perhaps, but that is low watts in light winds. Heavier winds it may turn 200rpm and you will get more watts. And in really hard winds you have to furl it away from the wind or it will produce so much power it may burn itself out or the rpms be so high it will fly apart.

 Unlike the gas genny, with a wind genny you do not have anything to set the rpm to any constant number. Rpm will change with the wind and also the power the genny is making will change. Keeping a load on it will prevent it from free spinning in normal winds which could damage it. Free spinning with no load could result in excessive RPM in light or normal winds, a load prevents this.

Watts/volts=amps. So your batteries will hold the voltage down to around 13-14volts untill they charge, then your controller kicks in a dump load to use up the extra power being produced so the batteries don't over charge. Severals way that can be done.

 In normal winds this is what would normally happen. In really strong winds or a bad storm the tail section pivots and the genny turns out of the wind to protect itself from over speeding. Other ways to do it also, but most gennies built here seem to use the pivoting tail.

So maybe in 8MPH winds you have cut in at 100rpm and are getting 14Vdc at 2 amps, 28watts.

Maybe at 10Mph winds you have 200rpm and get 14V at 6amps, 84 watts.

At 20 mph, 800 rpm, 14V at 45amps, 630watts.

At 45 mph and above you may need to be furled out of the wind to prevent over speeding or burning out your genny.

The numbers are just numbers for examples not acurate speeds or power, but you get the idea.

[Flux]

Try this link. My reply to coldspot should cover what you want.

http://www.fieldlines.com/story/2006/1/8/124746/5893

Flux

[DanB]

Yes - like flux said..

the blades need to run at a certain speed in relation to the windspeed to be efficient.  Most efficient blades run somewhere such that their tips are going round 5 - 9 times faster than the wind.  Shooting for a tip speed ratio of 7 is nice - you have a bit of room on both sides of that, because in reality, the tip speed ratio will probably vary a bit between the time the machine starts up, and the time it hits full power.

Before the alternator starts charging, the blades will be unloaded (Free spinning) and running at higher than normal tip speed ratio, so it makes sense to design your alternator for cutin in 6 or 7 mph winds with a fairly high tip speed ratio.  (if you design the blades for TSR of 7, then figure cutin should happen in a 6mph wind at TSR of perhaps 9) - at least this seems to work well for me.

To figure the speed of the tips, you need to figurer the circumferance of the blades (10' blades would sweep a circle with circumferance about 31.4').  Once you know how far a blade travels in one revolution, then you can calculate the rpm required for them to run at the desired TSR and design your alternators cutin speed appropriatly.

[nothing to lose]

I geuss we all posted at the same time.

Thanks for that explanation of TSR, I had the basic idea I geuss, but still fuzzy, that clears up a couple things for me too.

[IntegEner]

Not directly on this subject but worth a word or two is that some amazing things are being said here. First, if one is to figure the angle of incidence of the apparent wind to a blade tip moving at a TSR of 7 (the arctangent of 1/7), one arrives at an angle of only 8.1 degrees! This is like sailing upwind so close hauled that the boat is almost headed straight into the teeth of the wind and saying that this is the best of all headings for speed and power. For small wind generators, also, it is difficult to attain such TSRs without high, blur speed, possibly vibration-prone rates of rotation. Here in just 6 mph winds, the 10 foot diameter rotor needs to be going at about 120 rpm to reach this TSR. 6 mph winds! My hand held Kestrel wind meter shows this is a wind that can be felt by a person at ground level but just barely.

Certainly need good blades here, understood.

Knucks

www.integener.com

[finnsawyer]

Amazing or not this is the everyday world of wind power.  You can design your blades for lower TSRs, but then the alternators don't like it.  As you should well know, engineering design always involves compromises.  As it happens, rigid air foils, unlike perhaps sails, can provide lift from a small negative angle of attack to about twelve degrees.  Note that this exceeds your calculated 8.1 degrees.  Well, clearly one can't use twelve degrees at a TSR of seven as the lift will then be acting as a brake.  That's the reason for a four degree angle of attack.  Darn, another compromise.  As one moves toward the root the situation gets better.  Halfway down, the angle between the apparent wind and the blade plane will be 16 degrees, so one could use an attack angle of 12 degrees there, if one wished.  Note that as the mill diameter gets larger the tip speed drops for a given TSR.  It might be useful at this point to mention that both the lift force and drag force increase linearly with the width of the blade.  This would seem to imply that you can increase performance by reducing width to reduce drag.  But then you need to increase lift, which you can do by increasing the angle of attack to 12 degrees, if the geometry and TSR allows you to do so.  This is the reality that your theory needs to address.  

[IntegEner]

All this wouldn't be but just a few words back and forth except for the grant proposal resubmission in the works here involving funds nearly the same as the prize Paul MacCready of Aerovironment once won for the Gossamer Condor back in 1977 (recently researched). I have arrangements made with facilities and industrial contractors here as a team on this. Somehow I need to get the seriousness of some of this across, despite the nicknames.

The above was my back handed way of saying that the blades on these turbines deserve to be designed well. These high TSRs demand careful work. If anyone wants to see high TSRs take a look at the megawatt-plus turbines.

I honestly don't think that wind energy has answered for itself many of the questions that are being asked not only here but everywhere else as well. The drawn out, patient explanations just aren't holding water. Ask anyone.

I have put together a few wind rotators using ideas that seem to me to be valid and they work quite well on their small scale as are shown in images on the IntegEner-W website. I think I have both recognized good approaches taken by others and taken some worthwhile first steps myself in finding approaches that stress good blade design. Replies welcome but not necessary.

Anthony Chessick

www.integener.com

[finnsawyer]

Sounds to me like me you will be in competition with Windstor.  I understand they have a small unit up and running, and are planning 100 kw units.  You have some catching up to do.  Good luck in building a real system providing real power.

[IntegEner]

WindStor is not competing on this grant to my knowledge. I have met them personally at a trade show along with their Canadian partner, Dermond. They are doing strictly vertical axis while my effort is on a study of aerodynamics that applies to both horizontal and vertical axis. I have small demos that run exceedingly well and demonstrate ultra low blade drag and am now busy making units for others. The vertical axis companies of whom McKenzie Bay and WindStor are together just one of a number worldwide are prime customers for this demo unit, something to show off and even market themselves. If the author of these comments wishes to see the Wind Aerodynamics booklet of IntegEner-W he is welcome to send for a free copy via e-mail in order to make informed decisions about it himself. Power is power and theory is theory, both separately important (and both subject to errors and misinformation). I am frequently asked to try to sell existing wind turbines of a commercial nature but find myself more comfortable, instead, looking at just what it is that makes the blades turn. I believe opportunities exist in this as well. There, I said what has been needing to be said and hope that some of the questions asked of me are by now answered. Like a baseball player out on the playing field, I can be "booed" as well as all the others but have a name and reputation to protect with a few choice words now and then myself.

Anthony Chessick

IntegEner-W

www.integener.com

[finnsawyer]

You say you are making units for others.  Considering the paucity of hard data that you present it appears that they are buying 'a pig in a poke'.  You seem to think you can get closer to the Betz limit than the best presently available.  If so, provide the data.  As an engineer, you can figure it out.  Just do the work.  Hype just isn't going to do, and that's all I've seen here.  Define what you mean by 'exceedingly well'.  I suspect anyone putting up a windmill will consider it to be doing exceedingly well when he sees it turn.  And why not?  The velocity cubed term in the wind power equation forgives all manner of shortcomings in design.

As far as drag is concerned, all modern air foils are low drag.  The problem comes about for a high speed horizontal axis windmill, because only a very small fraction of the lift gets converted to usable torque.  This has the effect of amplifying the drag effects relative to what you would find for an airplane wing.  Since lift goes as the apparent wind speed cubed and drag as the apparent wind speed squared, one is probably still better off using a high value of TSR.  A higher TSR also means the alternator turns faster giving better performance there.

You can study the aerodynamics of windmills until Hell freezes over, but, until you actually build a complete system and show that its performance is superior to anything available you are just howling in the wind.

[IntegEner]

Geez, someone of quite good character who actually thinks I am important enough to warrant what appears to be an unending series of comments......Thanks for the time. It is quite appreciated. I am a poor person, a "church mouse", as they say and don't have the leisure to spend more time on this nor am I even worth it....Thanks again.

Anthony Chessick

www.integener.com

[finnsawyer]

Well, I try to be helpful.  One purpose of this site is the exchange of ideas.  If it appears someone is going down a blind alley, shouldn't we call that to their attention?  Some people tend to poo-poo the years of dedicated scientific research that has gone on before.  Others refuse to try to make basic measurements (the Bedini Controvery), and others just don't know how (the Pergomotor Saga).  Why shouldn't we make an effort to help them avoid wasting years of their life pursuing what amounts to a dead end.  

I also can learn things and develop insights based on these little discussions.  I hadn't given much thought to the deflection of the air by propellers, fans, or airplane wings.  It just didn't seem to have any relevance to the behavior of wind mill blades.  Since you thought that it was important, I conceived of a specialized experiment consisting of a long tube shaped wind tunnel with the windmill occupying essentially the entire diameter of the tube.  This eliminates any vortices off of the tip.  There are two possible directions for the air flow behind the blades; straight back, or tangential to the side of the tube.  The latter flow will constitute a vortex and will quickly dissipate against the side of the tube.  The problem is, that it may not exist.  Just because something could be there doesn't mean it has to be there.  Nature has a way of confounding our expectations.  If it doesn't exist your theory, whatever its merits, will have no relevance to the behavior of a horizontal axis windmill.  If it does, the resulting expanding vortex will affect the placement of wind mills in a wind farm.  Perhaps your first proposal should deal with this issue.  Maybe I'll do it myself.  What is the name of the the foundation involved?  I could use a wind tunnel.

[IntegEner]

It is the state, the State of California in the States. I am just poor, crazy Knucks, the "church mouse in a poke" as my nickname undergoes further adjustments.

Anthony Chessick

IntegEner-W

Tehachapi, CA

www.integener.com