Author Topic: vawt to go (Read 414 times)

electrondady1 · « **on:** August 06, 2007, 06:34:28 PM »

ten minutes worth of diagram,

an hour to re download my scanner software

half an hour to figure out how to change a bitmap to a jpeg!

electrondady1 · « **Reply #1 on:** August 06, 2007, 12:36:02 PM »

electrondady1 · « **Reply #2 on:** August 06, 2007, 12:41:59 PM »

ok,

seems to be working!!

so this is what i have been able to take away from wdyasq's post

and the ensuing dialogue.

if i have gotten it wrong please feel free to revamp the drawing

i have no c.a.d. skills

it's pencils for me

pepa · « **Reply #3 on:** August 06, 2007, 01:35:14 PM »

looks interesting, something to try. i was reading your post and doodled the drawing of a bottle nose dalphine shape laying on it's side with a yaw pivot about center of the head area. a vawt with only it's sails exposed to the wind mounted inside the structure and the vanes exposed below where rhe dorsel would be and the balance of the vawt hidden inside the structure as you show it. the wind would speed up over the curved portion and the whole thing would track the wind causing lift and speed increase. as the wing shape tried to rise or pull to the raised side the wind would hold it in check and give extra pressure to the vawt. just the way i see it, pepa

Dave B · « **Reply #4 on:** August 06, 2007, 04:10:25 PM »

I am no engineer and my terminology will probably not be correct but : The volume or mass of the air that would pass the area if there were no tree is being split in 2 by the tree. Yes, it travels faster around the edge of the tree but there is only half of it on either side. I guess what I am trying to say is that I always learned that you cannot create nor destroy energy. I have to believe that the total amount of energy available in the wind for that scenario at the turbines would equal that of the total wind energy before the tree. More mass x less velocity = less mass x more velocity or something like that. No need to prove the velocity can increase around the edge of the tree, that's called flying. I would love to see more talkers be doers and take their ideas to the shop. At least for the most part this type of discussion has now been moved over here from front page stuff to the Rants and Opinions, thanks to all envolved for that Dave B.

TomW · « **Reply #5 on:** August 06, 2007, 04:30:41 PM »

Dave;

Amen on the seeing more talkers be doers. I think we called it put up or shut up in my youth. Now days I can't call a turd a turd for fear of offending someone.

Cheers.

TomW

vawtman · « **Reply #6 on:** August 06, 2007, 04:46:02 PM »

Hi Edaddy

Nice coloring job

My thoughts would be to erase the tree or go above it.Trees can absorb alot of the winds energy.

I look at a tree has wind turbine in my skewed mind.

If your drawing has so presented would work the little airfoils(leaves and branches would remain silent has the wind eluded it.Instead it acts has an absorber like a turbine.

Sometimes trees blow over and lose blades(leaves and branches)Like some know with turbines.

Hope i didnt start a war again but seems common sense to me.

A solid cylinder or airfoil would force the issue.

My thoughts on the subject.

windstuffnow · « **Reply #7 on:** August 06, 2007, 05:31:55 PM »

It would work just fine as drawn. The power that could be extracted from the turbines would extend to only the exposed blade area on each side of the tube. It does help reduce the drag on the upwind side but also creates another problem as the blade tries to appear from behind the cup. The pressure in front of the cup and around it is a high pressure zone where the back side and inside it are a low pressure zone. As the "fresh" blade tries to pass the edge of the cup into the air there is a resistance because the air is also trying to flow to the low pressure side inside the cup and steals a bit of power from the exposed wing.

As far as efficiency it would probably be a bit low but it work fine as drawn.

.

vawtman · « **Reply #8 on:** August 06, 2007, 06:29:12 PM »

Hi Ed

Has drawn he would have to plant trees all around it with airgaps to let the wind through has direction changed.

Trees and turbines dont mix.My experience.Even with the vawt.

I agree with the ducted turbines losses fighting no wind on the inside.

windstuffnow · « **Reply #9 on:** August 06, 2007, 09:09:34 PM »

I assumed the tree was just an example of the wind flowing around it... also, assuming that no one would mount a turbine behind a tree.

.

wdyasq · « **Reply #10 on:** August 06, 2007, 09:55:13 PM »

The trees are mobile trees. The grow quickly and move exactly two compass points to the right and left of the apparent wind. You can't actually beat Betz with this setup. But you can grab a switch from one of those trees and slap him about a bit.

Ron

rossw · « **Reply #11 on:** August 07, 2007, 02:09:33 AM »

I can't resist.... I've tried... but... but...

If you have half the air moving at twice the speed.... and if power increases with the cube of the speed, then....

If we take the original air and say there was 10 watts per square metre of surface, you divide it in two (now half a square metre) but speed is twice as fast, we should have 30 watts (cube the 10) divided by two (half the area) - or a nett increase of 50%

(ok, I'm only stirring - it doesn't work like that, I know it, and you know it, but I bet someone will take this as mathmatical proof that it does - and I sure hope they are not readers of Douglas Adams' books!)

electrondady1 · « **Reply #12 on:** August 07, 2007, 07:15:03 AM »

ok, ok,you buggers !lol

i just put the image of the tree in as a reference to finsawers observation of nature .

in my location,(in town) at the heights i can build to,(25')

it's quite common for the wind to shift back and forth about 45 degrees.

this is the very reason a vawt is practical for me.

an add on that boosts power(a fairing) for one direction, interferes when the wind shifts.

unless,

you get the whole thing to pivot and face into the wind as pepa suggests.

we have now turned a very simple device into a complex one.

whatsnext · « **Reply #13 on:** August 07, 2007, 08:35:15 AM »

Wouldn't that just be a drag VAWT with a TSR<1 ? Let's have GeoM build one of these first.

finnsawyer · « **Reply #14 on:** August 07, 2007, 08:42:38 AM »

Why don't you just put the blades around the tree, and replace the tree with a nice smooth cylinder. I just know I'm going to exceed my allotted number of comments per day on this thread.

finnsawyer · « **Reply #15 on:** August 07, 2007, 08:49:09 AM »

I wouldn't do it that way anyway. I'd place a tube venturi type structure starting at the "zone of + velocity", otherwise known as the 90 degree line and channel the air to a HAWT. Oh yeah. You also replace the back half of the cylinder with a structure changing shape down to a tube. This whole thing must be made to turn to track the wind. It would be rather complicated.

finnsawyer · « **Reply #16 on:** August 08, 2007, 07:31:11 AM »

Well, RossW, you stepped into it. You came up with a logical argument. you should really avoid that, as the results just sit there staring back at you, bugging you. Actually your argument is rather weak. We can strengthen it by recognizing that Nature acts to keep the mass of the air flowing toward and around the tree or cylinder constant. Even that expert Peter will agree with that statement. So, in order to get that extra air around the tree Nature speeds it up. She could, for instance, cram all that extra air into a region around the tree from the radius, a, of the tree to a radius of 2xa. That would require a doubling of the air speed at the 90 degree plane. that would give 1/2x8 or four times time power flow through that plane out to a radius 2xa of the tree or cylinder. From there out the power flow would be unchanged. Well, Nature doesn't do it that way. That would require a shear in the air flow at radius 2xa. What one gets is a gradual drop in the air speed around the cylinder, which yields a peak power boost of 1.78 instead of four, which is still substantial.

One thing this last logical argument tells us is that the speed up of the air flow must extend beyond a radius of 2xa, which is consistent with observation.

finnsawyer · « **Reply #17 on:** August 08, 2007, 07:50:21 AM »

What you are not considering is that part of that total energy is contained in the pressure of the air as potential energy. As Peter has indicated, a shift in energy from potential energy to kinetic energy is allowed. This is what occurs as the air speeds up and the pressure drops in the flow around the tree or cylinder. Bernoulli's Equation is happily satisfied, but since the kinetic energy has gone up, with the corresponding increase in power flow, there becomes the possibility of harvesting more power from the modified flow, which, of course, is a recognized effect of hills. What is new about this argument is incorporating the effect in a contained structure. The windmill blade reacts to the speed of the air hitting it. It doesn't care about the history of that air.

fungus · « **Reply #18 on:** August 08, 2007, 07:54:47 AM »

'we should have 30 watts (cube the 10)'...10 cubed is 1000...

electrondady1 · « **Reply #19 on:** August 08, 2007, 11:27:05 AM »

" What one gets is a gradual drop in the air speed around the cylinder, which yields a peak power boost of 1.78 instead of four, which is still substantial."

i understand how there would be a gradation in the velocity . decreasing as one moves away from the cylinder.

lets drop the tree metaphor, as i have no intention of incorporating the effects of tree bark.

it is unclear as to how you arrived at a 1.78 boost factor

are you somehow averaging the increase over radious 2xa??

i ask this as a way to determine an effective ratio of the cylinder dia. ( fairing ) to the dia. of the vawt.

it has occured to me that the velosity of displaced air could be greater than 2x in close proximity to the cylinder surface .

windstuffnow · « **Reply #20 on:** August 08, 2007, 05:43:11 PM »

It almost sounds like an overunity conversation... There is no "boost" in power, the power through the turbine remains the same. You can increase speed but you also loose torque. I was caught up in the "boost" trap while experimenting with the Lenz turbine. The center of the turbine contained a shaped core that would increase the wind speed around the wings. It actually worked great using the venturi effect especially on the up wind side where the wing was traveling into the wind at the same speed the wind was comming in ( thus doubling the wind speed ). Calculating it out using the double wind speed was pretty amazing on paper. In reality my test showed the machine would spin quite a bit faster but with reduced torque. After removing the center drum the turbine didn't spin as fast but the torque came up considerably. Overall calculating the difference between the two showed about the same output in the same wind. I opted for larger wings in the same dimension and ended up with a higher efficiency.

Sorry, there are no free rides... the trick is to work on the conversion efficiency to boost output of the machine.

The biggest problem in extracting energy from the wind is the overall efficiency. That is to say, taking the wind and converting it to a useable form of electric in the shortest possible way. We can make a turbine that will extract energy at the Betz limit, that's the easy part. It boils down to our conversions that screw it all up. We have wind but we want/need 110vAC at 60hz ( or DC appliances ). So here is what we do to get it... Wind to mechanical energy, mechanical to AC, AC to DC, store it in batteries, DC to AC through an inverter to power low efficient devices. Each time we convert the energy to a different form there are losses. It's actually quite amazing we get as much as we do in the end. For instance... lets say there is 1000 watts of wind energy passing through the blades and we manage to get 60%, we filter it through an alternator that is 60% efficient, pass it down some wires - we'll call it 95%, convert it to dc and stuff in in some batteries 90% (if we're lucky ) then through an inverter that is 90% efficient. What is left for our use.... 270 watts out of 1000. When we pass it through some low efficient device were actually get to use 200 watts of all the work to get it there.

We need a computer controlled wind oscillator that converts wind to 120v 60hz AC on demand and then stores the unused portion so we can waste it later.

Anything come to mind?

.

vawtman · « **Reply #21 on:** August 08, 2007, 06:01:55 PM »

Well put Ed and Thanks

electrondady1 · « **Reply #22 on:** August 08, 2007, 10:12:39 PM »

yes thanks ed,

that's really insightful.

you have such a great overview on the process.

it never occurred to me there would be a reduction in torque

by increasing the velocity !

but of course it makes perfect sense.

found out a while back, how big a factor torque is the first time i but a load on an alternator.

i recall your first lenze turbine and how much better it became after you removed

the center section.

that dam brass ring , i's hard not to reach for it

finnsawyer · « **Reply #23 on:** August 09, 2007, 08:45:30 AM »

I pretty much stated the process in the thread under the other posting. Basically, you take the variation of the power flowing past the cylinder at the 90 degree plane as determined from the velocity profile and integrate it over the area from the cylinder radius "a" to a value of radius "r". You then divide that number by the power that would be flowing in the undisturbed air over an area from a value of radius from 0 to r. If one then plots this result as a curve versus r, it starts at zero at a value of r equal to a, rises to a maximum value of 1.78 and then drops back to 1 at large values of r. For those people who are calculus challenged you simply replace the term for area "A" in the power equation of the air flow by the differentials dr and dz. dA = drxdz, where now dA is the differential area. I hope this clears it up. The axis of the cylinder coincides with the z axis.

finnsawyer · « **Reply #24 on:** August 09, 2007, 09:02:31 AM »

In order to compare the two configurations adequately you need speed versus torque or output power at the same wind speed for different values of loading. You do not provide such data, so all one can conclude is that subjectively you liked one configuration more than the other without really having any idea of the true differences. You also say you had a shaped core, so there is a basic question as the what relevance that might have to the case of a smooth core. After all, your guesses could have been wrong from the start.

There is also the question of the accuracy of the tests. You may think the air speed is the same in both cases, but it may not be, or the way you measure it may be affected by the differences in the structure of the turbines or surrounding structures (the wind may have changed direction).

Norm · « **Reply #25 on:** August 09, 2007, 11:09:04 AM »

Ed....

We need a computer controlled wind oscillator that converts wind to 120v 60hz AC on demand and then stores the unused portion so we can waste it later.

I'm just a talker on this ...not a doer ...Yet

....

not necessarily computer? how about just mechanical? If you have need for a constant...

like an CFL that requires X amount of watts,

then you make a weight driven generator to provide the constant power by adjusting the

weight....as it unwinds the VAWT or HAWT is large enough that even in a 5MPH wind has enough

torque to easily rewind it...the WT don't even have to be efficient....just sturdy !

I realize that for even that takes quite a

bit of weight.... 1.5 pounds travels about 1 ft.

a second to provide about 200 ma @5-6volts to light a

small led lamp as near as I can recall from some

experiments that I had done a couple of weeks ago.....( I was the winder constantly pulling it

up capable of hoisting it up 5 times faster than

it could unwind.)

( :>) Norm.

windstuffnow · « **Reply #26 on:** August 09, 2007, 05:55:34 PM »

I like the way you think Norm, I've been working on a project, off and on as time allows that does precisely that. Only difference being is it uses springs not weights. Springs can fit in smaller packages and still pack a pretty good punch. As easy as it sounds it is quite challenging.

I've built a few "wind oscillators" that are quite powerful for their size. The biggest drawback is finding the off balance in different winds. The easiest example of what I'm talking about would be the wind blowing through a set of venitian blinds on a breezy day. One or two of them will take off and make a heck of a racket. A good example of the power is aileron flutter in an aircraft, once set in motion it will destroy itself. I think it would take a computer controlled weight to maintain the oscillations through varying winds. Just another hairbrained idea I'd like to pursue.

.

Norm · « **Reply #27 on:** August 10, 2007, 11:50:20 AM »

Yep...springs are nice also for that purpose,

I've got the very thing....it was an antique

even before I was born....a wind up 'Victrola'

play a record,wind it up,play another record..

etc.or you can wind it up slowly and continually,

wonder if that would run a stepper motor hooked

to a led direct drive....

( :>) Norm

BTW what are the dimensions of the Lenz turbine

you have on your roof?

windstuffnow · « **Reply #28 on:** August 10, 2007, 01:23:24 PM »

It's a little one, 3ft diam x 4ft tall. Very seldom does it stop. It cut's in at around 30 rpm and does it's constant charge day and night.

I'll probably have to take it apart next year though, the wood in the wings is starting to show some deterioration.

The only real problem I've had with it was in mid winter after a freezing rain the icesicles froze at a strange angle while it was spinning. Started making all kinds of noise as the Ice hit the frame and broke them off and as you can imagine the balance was thrown completely out of wack. Nothing I could do at the time as the roof was so slick there was no way to get up there. It was pretty noisy for a couple days.

.

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Author Topic: vawt to go (Read 414 times)