Author Topic: NEW! And revolutionary VAWT . (Read 665 times)

dinges · « **Reply #33 on:** August 02, 2007, 11:33:12 AM »

You read selectively, don't you?

"That is a strange statement since everyone knows that if you speed up a mass it has more kinetic energy."

Notice how I said: "with e.g. a venturi". Notice how I was also in another part talking about the TOTAL ENERGY staying THE SAME if you don't put extra work or extract WORK from the air.

Which was an example to show how its possible to increase the speed of air WITHOUT adding extra energy. A Venturi manages to speed up air and decrease the pressure whilst TE stays the same.

"Similarly, if you compress a gas its internal energy increases. "

If you COMPRESS energy you put WORK into the gas, hence you INCREASE its energy

"What I don't understand is why someone like yourself, who claims to know all the fundamentals, chooses to ignore a simple challenge. Is it because it wasn't presented by a Professor in a class room?"

Are -you- now asking -me- to prove -your- erroneous ideas ? Just like a while ago you challenged -someone else- to build -your- generator design to prove -you- are wrong ? Isn't that the world reversed?

Is that the scientific method they taught you at MIT ?

I was taught to disprove my own theories and ideas.

As good old Edison said, 'Genius is 1% inspiration and 99% perspiration'.

You want me to do the perspiration for you?

electrondady1 · « **Reply #34 on:** August 02, 2007, 11:50:41 AM »

i do enjoy the intellectual fencing matches that occur here occasionally.

it's important though to remember scoring points is not why we are here.

far be it from me to defend fin's theories.

but i have also observed the phenomenon he mentioned in regards to wind, snow and tree trunks.

i have become a keen observer of snow drift patterns since i became infatuated with wind mills

i think there are lots of lessons and possible benefits from it.

Countryboy · « **Reply #35 on:** August 02, 2007, 10:17:19 PM »

There is an interesting phenomenon that shows up around here, which you may never see where you live. We get upwards of three feet of snow on the ground in the woods. There will appear around the trees a saucer shaped depression that extends out about one radius from the tree. Now, this is not due to the sun, which never shines on the north side of the tree in the winter. It must be due to speed up of the air as it goes around the tree. This speed up, which is twice the incident air speed, means there is available eight times the energy next to the tree trunk to scoop out the snow.

Where do you get the idea the speed up of the air is TWICE the incident air speed? The change in airspeed and pressure is miniscule - however, that change in airspeed is just enough to keep snowflakes suspended in air as the air goes by the tree.

The tree acts as a venturi. The snow is deposited in the low pressure areas outside the tree.

What you fail to see is that the total energy of the airmass is actually slightly higher than the energy that airflow has. That is because of something known as friction and resistance.

Get rid of all those trees that are providing resistance, and you'll find that your windspeed will actually be faster than it is when it has to blow past trees.

I'd recommend you study how a sluice works to understand the phenomenom you describe. Think of the water flowing over the sluice as the wind, flakes of gold as your snowflakes being moved by the flowing mass, and think of the riffles as the trees.

finnsawyer · « **Reply #36 on:** August 03, 2007, 08:46:17 AM »

"Where do you get the idea the speed up of the air is TWICE the incident air speed?"

Any time I walk between two buildings when the wind is blowing I get the effect in my face. This doubling of the air's velocity is not due to me. It has been well known for a long time. In the 70's I saw a proposal for making use of the effect by placing a wind mill on a track around a circular oil derrick. That's not really relevant here. What is relevant is that the mathematical solution for fluid flow around a cylinder exists. It is either correct or wrong. If it is correct than the statements I make follow from an analysis of the situation, something anyone with a rudimentary knowledge of calculus can do. If it is wrong, prove it.

"The tree acts as a venturi. The snow is deposited in the low pressure areas outside the tree."

For the tree the low pressure area is near the tree.

You people want to compare this with a Venturi, which comes about as a result of lowering the air pressure on the output end. You need to look at a Venturi where the air blows into it. You could measure the pressure in the Venturi and some distance before the Venturi to determine the relative velocities and from that determine the power flow in the Venturi relative to the total frontal area of the structure. In any case the process satisfies Bernoulli's Equation, which, by the way requires the internal energy of the fluid to remain constant, so thermodynamic considerations do not apply. The comments about the tree's resistance just obscure the issue.

finnsawyer · « **Reply #37 on:** August 03, 2007, 09:06:02 AM »

My building it wouldn't prove anything, since I don't have access to a wind tunnel to make the accurate tests that are needed. All you have to do is read this thread and others like it to see that anyone making any claims that look too good isn't believed anyway. That doesn't mean we can't discuss the theory. There are people frequenting this site like the fellow I'm been having this discussion with that certainly have the ability to do the analysis to test the validity of my conclusion. What is mysterious is that everyone seems to think I'm trying to pull some kind of fast one. I could present the analysis, but chose not to, as I'd like to see what others might come up with independently. I could be mistaken, but all the evidence I,ve seen seems to bear out the conclusions: One could get a power boost of 22% with a sphere or 78% with a cylinder.

finnsawyer · « **Reply #38 on:** August 03, 2007, 09:27:15 AM »

I don't know why you emphasize a 'Venturi' since it does not aply to this case, as I point out in another comment on this thread. You might check the other comments.

Actually, I'm inviting you to disprove my 'erroneous' ideas. But we need to start from a common point, which would be the known solutions for fluid flow around a sphere and a (long) cylinder. If you chose not to accept them and their ramifications that's your choice. But they are out there.

I think you're a bit off base with some of your criticism. If everyone was expected to disprove their own ideas nothing would ever happen. It is only through the cross fertilization of ideas that different perspectives quickly become apparent. That's why people publish. Is your attitude of shooting down new ideas without testing them indicative of how you do things in Europe now? No wonder Europe is stagnating.

Countryboy · « **Reply #39 on:** August 03, 2007, 10:41:24 AM »

Actually, I'm inviting you to disprove my 'erroneous' ideas.

George,

You can't prove a negative. Only an idiot attempts to do that.

It is YOUR responsibility to prove your assertions. No progress will EVER be made if everyone is wasting their time disproving erroneous things. Progress is made when people put their time and energy into proving good ideas.

Countryboy · « **Reply #40 on:** August 03, 2007, 10:49:27 AM »

Any time I walk between two buildings when the wind is blowing I get the effect in my face. This doubling of the air's velocity is not due to me.

Once again, where do you get the idea the windspeed has doubled? The speed may have increased, but that does not mean it has doubled.

For the tree the low pressure area is near the tree.

The area right around the tree is the high pressure area. Air pressure is increased because of the resistance of the tree. Go punch a wall - your hand won't hurt in the low pressure areas. Use that as a guide to determine where the low and high pressure areas are.

In any case the process satisfies Bernoulli's Equation, which, by the way requires the internal energy of the fluid to remain constant, so thermodynamic considerations do not apply.

You have already alluded to Bernoulli's Equation as not applying, simply because you discount the idea the total internal energy of the fluid remains constant. You have already stated the internal energy changes as the fluid flows around objects.

dinges · « **Reply #41 on:** August 03, 2007, 06:51:26 PM »

Countryboy,

One can not prove one is right, one can only prove someone is wrong. Which is why hypothesis should be made in such a way that they can be falsified. The fact that a theory is accepted doesn't mean that it's correct, it means just that we haven't been able to disprove it yet. If not, it's pseudoscience.

The scientific method indeed relies a lot on peers disproving theories of others.

I will not be taking up GeoM on his offer though; in post #36 he stated that 'thermodynamics do not apply'. If he believes that is correct then I could never convince him. He has just discarded the most fundamental principles of physics (the laws of thermodynamics are the foundation of physics). Without these laws it's no longer physics but theology.

As RonB said, they apparently not only retracted Betz but also retracted the Laws of Thermodynamics. A new day is dawning indeed.

That's the first thing.

Secondly, I think I can spend my time in better ways. One thing I've learnt over the past decade is that one should learn not to argue with just about everyone on the internet. I reserve that argueing for only a few special people.

As to the Venturi effect; GeoM seems to think it doesn't apply to his tree/building example.

I say it does. A venturi is representative of an obstruction of the airflow, just like a tree. Air passing that tree will speed up and as a consequence (because total energy MUST stay the same) its pressure gets less (yes, less). This means too, btw, that rho gets less, i.e. the air becomes less dense and can do less work because of that. It can do more work because of the higher speed. The two will perfectly compensate eachother as the energy can not magically appear or disappear (ignoring friction; but even with friction it wouldn't change TE: TE = potential energy + kinetic energy + thermal energy = constant)

Notice that as the air speeds up, the 'mass' of air that passes through the windturbine per unit of time doesn't change. And neither does its total energy. If its kinetic energy increases, it will come out of its potential energy. And notice that Betz doesn't say you can extract 59% of kinetic energy but 59% of the -energy- of the wind.

As I said, a tree and a venturi have a thing in common: they're both an obstruction to an (imaginary) cylinder of air. GeoM fails to look at a venturi as anything else than 'a tube'. And that's how it's usually drawn in the textbooks. Truth is, there are lots of venturis in the real world, with or without a physical tube. Bernouilli still applies, with or without any physical tube. Whether it's a tree in the field or an Althaus venturi mounted on a Ka-8b.

So, counterintuitive as it may seem at first sight, pressure gets REDUCED as the wind speeds up.

Hope this explains it a bit Countryboy. If not, pop in in IRC sometime again; missing the odd discussion with ya.

Regards,

vawtman · « **Reply #42 on:** August 03, 2007, 07:47:53 PM »

Why dont you guys just build a turbine and take what you can get?Then worry later on if your not happy.

TomW · « **Reply #43 on:** August 03, 2007, 07:58:04 PM »

vawtman;

Peter does build [at least one alternator anyway] which should say something.

Just to put a proper light on things. Doer, Not Doer. You draw your own conclusions.

The proof:

http://www.anotherpower.com/gallery/album46

Cheers.

TomW

dinges · « **Reply #44 on:** August 03, 2007, 11:47:13 PM »

For completeness sake: Betz says you can extract maximum 59% of kinetic energy, not of (total) energy. My previous remark was incorrect.

Vawtman, I agree with you (gasp; what's next ?! .This is all idle chatter if it doesn't result in better windgenerators. Seriously. I disagree with quite a few things you do/build, I think there are better/simpler ways to achieve the goal, but in your defense, you build and don't just armchair philosophize about it till you see blue in the face. At the end of the day theory is just theory. The proof is in the flow of the electrons.

I've been following your large wheel/wooden stator radial flux with interest though I would do just about everything differently from you But that's ok, it's your project. You do yours your way, I'll do mine my way.

Ah well. At least we both would like to stay in Oztules' container/luxury apartment. I haven't received an invitation yet though [hint, hint, Oztules].

Just so you don't get the wrong idea about this entire discussion.

Regards,

oztules · « **Reply #45 on:** August 04, 2007, 01:41:44 AM »

You don't need an invite Peter.

Anyone who is prepared to spend their time to selflessly do a complete thesis on decogging steel stator machines in the interest of the many..... is instantly recognised as family.

Bring your own toothbrush though. (if Ron turns up a gas mask may be in order as well)

...........oztules

finnsawyer · « **Reply #46 on:** August 05, 2007, 08:55:41 AM »

Look, I believe I have two said two things about the situation. One is that Bernoulli's equation applies. No external work is being done until snow is removed around the tree. Secondly, there is a mathematical solution to the problem that predicts the doubling of the speed. I assume you accept the proven fact that the air speeds up and the pressure drops around the convex side of an air foil, but when faced with a different situation that obeys the same physical laws you then say it can't be. If you split the cylinder in half along a plane parallel to the direction of air flow you get two air foils. The convex side of each resulting foil is the side where the air speeds up and the pressure drops. Have you ever wondered why the leading edge of an airplane wing is rounded rather than brought to a knife edge. The obvious answer is that that gives the greatest boost to the speed of the air across the top of the wing and consequently the greatest lift while giving the best lift to drag ratio.

As far as the internal energy is concerned, if you Google "Bernoulli's Equation" you will quickly find a paper that derives the Equation from the stipulation that the internal energy remain constant. When the air goes around any obstruction, including the tree, the speed up of the air is effected through a drop in pressure. If you study Bernoulli's equation carefully, you will find it is actually an energy equation that says the total energy is constant. But part of the energy is contained in the pressure of the fluid. If that pressure is reduced, then the fluid must be moving faster to keep the energy in balance, which means more energy per unit time or more power will be moving across a unit of area. How that energy flow is distributed depends on the problem. Again, the solution for a cylinder states that the power flow is enhanced in a region around the cylinder. This is possible and violates no Laws because the pressure is lower in that region, again, due to the physics of fluid flow.

finnsawyer · « **Reply #47 on:** August 05, 2007, 09:07:26 AM »

You can prove the results to be wrong. That is, a 22% percent maximum increase in the power available from the flow around the sphere or 78% around the cylinder. It should take you less than half an hour to set up the problem and do the integration once you have the solution for the flow around a long cylinder.

You are big on the Venturi. You state there is no change in power flow in a Venturi. So, prove it. We have a fluid of density rho flowing in a pipe of area A at velocity V. The pipe gradually reduces to a cross sectional area Of A1. What is the ratio of power flow in the smaller region to that in the larger region? Perhaps, you only need look this up.

finnsawyer · « **Reply #48 on:** August 05, 2007, 09:57:25 AM »

For a minute there I thought you had deflated the argument with the "new" interpretation of Betz. In that case, what I maintain wouldn't be an issue for you, since the increase in energy flow per unit time comes from the energy available from the drop in pressure or the potential energy (see my latest response to Countryboy). That's the crux of the issue, as Bernoulli's equation is really a conservation of energy equation. In order to get the air to flow around the tree (or sphere or any obstruction) nature takes energy from the potential energy (pressure) and transfers it to the kinetic energy. This gives a 78% increase in the kinetic energy in the region around the tree, which is potentially available for harvesting. It is similar to the effect of a hill, where a VAWT will harvest more power than on the plain. The difference is that it can be made part of the structure and controllable.

You are the one who introduced thermodynamics with your statement about entropy. If, as you suggest, the density changes, then one would need to consider thermodynamic changes. I have seen no evidence of such a need and the model I am using does not require a change in the thermodynamic quantities. I was trying to convey that that was my position.

"Notice that as the air speeds up, the 'mass' of air that passes through the windturbine per unit of time doesn't change. And neither does its total energy."

I think you are going to want to retract this statement. It's pretty well accepted that for a turbine in free air, if the wind velocity doubles, then the power flow or energy per unit time through the turbine will increase by a factor of eight. Why don't you take a hard look at the step down 'tube' Venturi, as I suggested.

dinges · « **Reply #49 on:** August 05, 2007, 10:30:33 AM »

"Notice that as the air speeds up, the 'mass' of air that passes through the windturbine per unit of time doesn't change. And neither does its total energy."

I see how that statement could cause misunderstanding/misinterpretation. Replace 'windturbine' by 'venturi choke'. I'll say a few more things (which you can easily verify for yourself: the massflow (per unit of time) doesn't change. The volume flow (per unit of time) doesn't change. The rho (density) doesn't change.

You still haven't made clear, btw, why you think a windturbine is different from a venturi (apart from the obvious fact that a windturbine extracts energy where a venturi doesn't). Both present obstructions to airflow. Bernouilli applies.

FYI, I have worked the problem out. God knows why I bothered anyway.

Betz is NOT beaten. You can not extract more than 59% of the kinetic energy of the wind.
more kinetic energy is available for more power as the wind speeds up (hint: what happens to the temperature of the air as it passes through a venturi?)
it's all a matter of drawing your system boundaries properly, as I stated before. If you do this 'creatively' as you do here (post #23), you can INDEED 'beat' Betz...

"It is quite possible that structural items necessary to the construction of the VAWT might produce a sufficient speed up in the air to beat Betz relative to the undisturbed incident air flow."

We measure surface area at the windturbine, but we measure windvelocity a few km off, before the hills/buildings have messed with the undisturbed incident air flow.

Last time I saw such creative playing around with figures was when I had to balance the budget for my department.

4) it has been a major waste of my time and effort. And 5 pieces of paper.

You may ask why I don't submit the proof here. I have my reasons. I suggest you do your own homework. You will not be getting another free ride on my back. I have seen so far not a single calculation or direct reference from you to anything. But many vague remarks without proof or references: 'wind doubling', '78%', '22%'. As far as your model goes, I have no idea what you are talking about. I have not seen any model. The only model I have is the one I drew up a few days ago myself.

So, I repeat what I said in my very first (and second) reply in this thread and which you didn't seem to agree with: Betz can not be beaten. Which was what this entire thread, as originally posted by Ron, was all about.

And this, for me, closes the case.

dinges · « **Reply #50 on:** August 05, 2007, 10:57:38 AM »

What I forgot:

You say correctly that as windspeed doubles, kinetic energy goes up 8 times. However, in that case WE PUT EXTRA ENERGY IN THE WIND! Mother nature lets the wind blow harder so more kinetic energy in it.

In the case of a venturi, or your hills or buildings, they do NOT put extra energy in the wind; there is an exchange of potential energy to kinetic energy as the wind speeds up. Laws of thermodynamics state that total energy MUST stay the same.

In the case of a venturi (or your buildings), as airspeed doubles, mass flow does NOT increase. Volume flow does NOT increase. And, rho/density does not change.

When the wind blows harder these things (mass flow/volume flow/rho) may change. But it's an entirely different situation: mother nature puts more energy in the wind in the first place. Your buildings or hills can not do that. So, apples and oranges: in both cases (venturi vs. mother nature) airspeed goes up, but in one case total energy of the air stays the same, while in the last case (mother nature) total energy goes up.

Now if you'll excuse me. I have some work to do on a motorconversion.

vawtman · « **Reply #51 on:** August 05, 2007, 02:00:47 PM »

Peter and Fin

It would seem to me standing inside a fat bladed darrius contraption that the blades speed the wind up without mother nature or funnels.

Try it sometime.

Have fun

finnsawyer · « **Reply #52 on:** August 06, 2007, 08:54:19 AM »

I see that I miswrote when I said energy. I should have said power. To clarify, when the wind speeds up by a factor of two, the power or energy per unit time per unit frontal area increases by a factor of eight. This sort of thing occurs any time the air is sped up including when it goes around an object. In the case of the cylinder at the 90 degree line as measured relative to the line of highest pressure (zero degrees) there will be a velocity distribution. If one integrates along this line from the radius of the cylinder, a, to some value of radius, r, one will find the power flowing past the cylinder to that radius at that 90 degree angle. If one allows r to vary, the result will be a curve that starts from zero (where the velocity is greatest) and increases. If one then divides that result by the power flow in the undisturbed air taking it from 0 to r, one then gets a curve that reaches a maximum of 1.78 and then goes to one at large values of r. I don't see why you are having such a problem with this idea considering that you are quite willing to concede that nature obviously transfers energy from the potential energy or pressure to the kinetic energy, which then determines the power flow. The question then becomes whether it is possible to tap into this increased power flow. I believe it is, based on the observation concerning the scouring of the snow around a tree. And if we can channel this higher power air to an air foil keeping the 78% boost then we have effectively beaten the Betz Limit as applied to the incident air flow. This type of effect would occur for any Venturi structure (using your definition) being part of the turbine, particularly for VAWTs, since they inherently require structures other than just blade assemblies. One would think that there would be considerable interest in exploring these possibilities.

As far as the density is concerned, I suppose one could study the difference between water flow and air flow around a cylinder in some sort of a fluid tunnel, but it is generally considered that for low wind speeds we can neglect the change in density.

finnsawyer · « **Reply #53 on:** August 06, 2007, 09:28:07 AM »

Why do you even frequent this site (not to mention the IRC) if your time is so valuable? These issues need not be settled in a day.

As I understand it the Betz limit applies only to the part of the air stream having the same area as the hypothetical turbine when it reaches the turbine. A Venturi can change both the rate of mass flow and the kinetic energy locally. This in turn can have a great impact on the power flow locally through the turbine.

You say you did the problem, but you do not present any results, other than a general statement. What did you get for the power passing the cylinder along the 90 degree line or plane? See my other comment of this date for an explanation. It would be nice if we were comparing the same quantity. The whole thing boils down to power. As you correctly imply nature operates to keep the total mass flow constant. This requires a speed up in the flow around the object, which in turn increases the power flow past the object compared to the undisturbed air. It is the net increase in this power flow that is of interest. What did you get for the maximum value of that power flow as compared to the undisturbed air? Remember, the power goes as the cube of the velocity!

finnsawyer · « **Reply #54 on:** August 06, 2007, 09:46:48 AM »

I'm not surprised. When the air passes over the air foil it is sped up. That's what makes the thing work. Wind tunnel tests show the difference in air speed along the top and bottom of the foil can persist after the two streams leave the foil. This can result in the effect you detected. The wake of the most windward blade could affect one of the other blades and, who knows, improve performance. But this would open up another can of worms, and I can't get any kind of agreement on the existing can. You're on your own on that. Maybe you could try a smoke generator to see how the air is flowing.

finnsawyer · « **Reply #55 on:** August 07, 2007, 08:27:14 AM »

"You still haven't made clear, btw, why you think a windturbine is different from a venturi (apart from the obvious fact that a windturbine extracts energy where a venturi doesn't). Both present obstructions to airflow. Bernouilli applies."

What is your authority for the statement that Bernoulli applies for the case of a wind turbine removing power from the wind? That would imply that the internal energy of the air was remaining constant as the velocity of the air was reduced due to the loss of kinetic energy. Bernoulli's Equation would then require that the pressure must rise to balance the equation, which puts us in the uncomfortable position of having the potential energy rising at the same time as the total energy was decreasing. It doesn't seem reasonable. It seems more likely that the internal energy of the air must also change, which means Bernoulli's Equation would not apply.

finnsawyer · « **Reply #56 on:** August 08, 2007, 09:28:05 AM »

"ONE MUST REMEMBER that no wind mill will be able to HARVEST more energy than the wind can have at any time."

This is obviously true, but the the Betz Limit only deals with the kinetic energy, not the total energy. The kinetic energy can increase without changing the total energy due to the presence of a "Venturi" structure. This in turn results in a greater power flow due to that "velocity cubed" term. It is odd that something that should be fundamentally obvious can generate such resistance. In fact it should be obvious that in an ideal step down down tube type Venturi where the area is cut in half that the speed must double to keep the mass flow constant. This results in four times the power flow due to that velocity cubed term (1/2x8).

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Author Topic: NEW! And revolutionary VAWT . (Read 665 times)