Wind Turbines

Unless you live somewhere where the wind always blows the same direction, your windmill generator swivels to catch the wind. Are you also going to swivel the funnel? Think of how big that thing has to be in order to be effective. Its mouth must be many times larger in diameter than the windmill propeller blade, and in order to not develop too much back pressure, the length of the funnel between the large opening and the opening at the windmill end must be many times the diameter. Doesn't seem terribly practical to me.

It is feasible to use architectural or geographical features which enhance the wind speed, I believe it has been done on occaision. I'd expect it also gives greater variatiion in wind speed and turbulence which would be a bad thing..

As they say up North "You don't get owt for n'owt"

I actually get an enhanced pressure difference between the front and back on my house, so when I open my garage door the wind whistles though, I've toyed with the idea of using this for a small wind turbine or supplementary summer ventilation. I toy with these ideas but they often escape before I can really pounce on them

Del

The most obvious reasons are cost, weight and the fact that even "low wind" areas are subject to storms. The turbine blades can feather to limit the speed and loads on the tower due to storm winds. A venturi would not offer that capability without immense expense and complexity.

"No such thing as a silly question. There are however lots of silly answers." Source unknown

The responses I've seen to your inquiry have pretty much summed up the basic reasons why it would prove ineffective. I'll add some more.

The plate effect of the "funnel" frontal area, if translated instead into the disk area of a larger diameter turbine, would likely prove more effective and more efficient than the funnel and a smaller fan. It would prove a lot simpler to build as one respondent has pointed out.

Like many things, it seems like it should work. Even ducted fans, with tightly fitted shrouds, have failed to demonstrate the kind of thrust increase that was anticipated by containing tip vortices's. It never happened. The cost of applying the technology was higher than the benefits derived.

L. J.

Silly? Perhaps. After leaving the funnel (which must not interfere with the sails), won't the increase in air velocity within the funnel be immediately reduced back to "natural breeze" velocity?

There were many valid reasons submitted why the funnel wouldn't be practical (including my own :-) but saying the wind velocity would slow down before hitting the sails isn't one of them. If you were going to build a funnel you would build the narrow end just slightly wider in inside diameter than the outside diameter of the sails, and the sails would fit just inside the funnel's narrow end, so that all the wind collected by the funnel would push past the sails and spin them. I'm not making this up: it is exactly how wind tunnels work, except in reverse of course!

"After leaving the funnel (which must not interfere with the sails), won't the increase in air velocity within the funnel be immediately reduced back to "natural breeze" velocity?"

If that were the case, then jet engines would cease to work a short distance down stream of the turbines.

I suspect that of more relevance is that everything being equal, for a given amount of power in, a slow turning large prop is more efficient thrust wise than a smaller one turning faster.

I see no reason why the blades on a turbine generator aren't influenced by the same principle. This will likely explain why all the wind farms I've seen are powered by slowly rotation big turbines.

L. J.

Why not just attach the funnel(s) to the sail(s)?

"No such thing as a silly question. There are however lots of silly answers." Source unknown ...... from post 4

So here is silly answer no. 1

Hi....it's the gaps between the mountains which acts as the venturi. There are several such geographical locations around the world. One such in South India being the Palaghat which is a 13km wide break in the Western Ghats and facilitates a mediun strong steady wind from the Indian Ocean flowing inland. The area is dotted with wind turbines. It allows a short taking-off run for aircrafts flying out of Coimbatore airport.

India has the world's 3rd largest wind installations.

I have a er stupid question,

The venturi effect if I remember correctly, also comes with a drop in pressure as the velocity increases. If the pressure decreases does this effect the pressure differential across the wind turbine blade robbing power?

Brad

Not a stupid question at all. The Venturi effect applies to an incompressible fluid, not a gas, which is highly compressible. Picture this: If an incompressible fluid enters the funnel, then because the fluid is incompressible, precisely the same amount of fluid must immediately exit the funnel as is entering. But if what is entering the funnel is a highly compressible gas, then initially the air entering the funnel increases the amount of air in the funnel (the density increases) until the resulting pressure build-up overcomes the back pressure of the funnel/propeller combination, and begins to push air out the narrow end. In effect, the air entering the funnel is doing work on the air already in the funnel, and increasing the potential energy of the funnel air, which is of course turned into the kinetic energy of the spinning generator. Hope that helps.

So then the pressure drop would be across the propeller in the funnel? Never mind

Just found the Bernoulli's effect|equation in my fluid mechanics book "... for steady frictionless incompressible flow ... " Mixing apples and oranges, thank you for the point in the right direction.

Brad

The Venturi effect applies to an incompressible fluid, not a gas.

Damn...the carburettor on my old Lambretta has suddenly stopped working now you've said that .
Retract that nonsense immediately and restore normal functioning of the universe.

Del

So back to my original question er sort of: As the pressure drops from 14.7, a percentage, the velocity increases but the density drops, so does this cause a loss of efficiency for the turbine due to a lower pressure diferental across the blades?inquiring minds want to know

Brad

Your carburetor, and mine, still work. More about that in a moment. The original question regarding the venturi effect was would it cause a loss of power to wind turbine blades at the apex of a wind-collecting funnel. Fundamentally, that doesn't happen because regardless of the venturi effect, the air captured by the wide end of the funnel is passing through the narrow end and hence has passed through the blades. Conservation of mass and energy dictate that the blades will be turned by some combination of wind velocity and pressure, and the overall energy turning the blades is the same as that entering the funnel - minus minor frictional losses. Now to the carburetor. While the venturi does indeed speed up air flow through it, and (minutely) decreases pressure relative to that coming into the venturi tube, that is not the important source of low pressure that draws fuel from the jet. The intake cycle of the engine is the source of vacuum that draws air through the carburetor. On the intake manifold side of the carburetor, there is lots of vacuum, and that is what draws the fuel out of the jet. My sense of what the venturi does is to speed up the air flow, which helps in atomizing the fuel. It also increases the vacuum at the jet by (minutely) restricting the amount of air coming in from outside. If there were no venturi at all, there wouldn't be much vacuum because the atmosphere would immediately fill the vacuum left by the descending piston during the intake cycle (nature abhors a vacuum). But note the venturi restriction is very mild - you can't seriously restrict air flow into the engine without major performance degradation. So the venturi effect alone does not create the suction - that comes from the descending piston during the intake cycle.

------ The Venturi effect applies to an incompressible fluid, not a gas, which is highly compressible.-------

Not correct! How do you think a Pitot Static Tube Airspeed Instrument works? Also Carburettors rely on pressure drop below ambient in the Venturi.. They, and many other applications rely on the Venturi Effect in compressable gases.

I agree a carburetor relies on the venturi to draw the gasoline at a low pressure into the air flow. Like Bernoulli predicted a velocity change causes a pressure change. As for the pitot tube, it relies on the mechanism I have seen in fluid mechanics books called "stagnation pressure" which is something different.

This is when the air molecules are slammed to a stop at the pitot tube orifice. Wait a minute! This may be partially at work when a propeller is being driven by wind. Increase the wind velocity with a cone and the stagnation pressure against the blades increases. Or maybe the air being compressable..... ack, must stop brain hurts! (spoken like Captain Kirk)

"The Venturi effect applies to an incompressible fluid, not a gas. . . "

WHAT?!!

Though true, it is impractical for the reasons explained in post 2. But, if we keep the metal funnel vertical with smaller end up and put some wind turbine at the top, as air gets hot inside metal funnel, it should rise up just as in chimeney and give good thrust to wind turbine.

I remember hearing this idea, which probably in working, somewhere in Australia.

Though it is bit off topic, may be of great interest to many of us.

It has been done- on a small basis- a square box, with large opening, free to face into the wind because of a tail, the box on a pivot- inside an alternator with a fan blade- the exit smaller than inlet- the alternator spins so fast have to gear down fan drive- which also gives more torque in lower winds.

While it is impractible to have a funnel in conventional wind turbine , but geographical location can help generate same effect and many site their wind turbines accordingly.

For low wind areas one can go for other types of wind turbine . A vertical S type with shaft at centre ( Half Cut drums) or have more blades with Horizontal shaft turbine in stead of 2 0r 3.

May be we can think of a wind turbine which has pack of blades . In good wind, three blades can be seen to operate and at low winds each blade can become wider or may be of 4 blades each( like pack of cards) . This can still run at low speed. When speed increases again it is back to 3 blades !! Silly idea ?

You are correct "silly question"

Tmf

You know I had a similar thought a while back, one could have rows of trees or some other converging setup in a spoke like fashion to direct and accelerate the airflow. The wind generator would be in the middle. I would say, it just might work!

It has been thought of and tried, without much success, so don't worry anymore that you are sitting on a world-saving idea. Thanks for letting us know, Kobender, and keep thinking.

Up here in Derbyshire ( where as Del says we don't get owt for no'wt) there is a farm in a shallow valley, facing out towards the Cheshire plains. Behind it is a main road with a ''dangerous crosswinds' sign on it, and I have seen vehicles blown well into the field downwind of this road.

Interestingly they are often facing the road quite neatly, because the engine weighs the front down slightly more than the back. That would be a place for a wind turbine, but the local park planners don't allow often, because they say it spoils the look of the area. If we don't do something soon, there won't be any park left.

When I was a boy I could easily see Wales. Now I can easily see pollution, there aren't any clear days anymore. Don't know what to say to my little ones....

Jim

Hi All, as an inventor, here is one of my wind ideas. I lived on a 200 ranch that had at the top elevation a domed hill. The winds were naturally strong and would come in all directions. I would like to talk to someone about engineering, turbine design, reduction gearing and possible funding. This design is an idea that I think answers many problems with wind generation. Imagine a flatten covered domed circle that has maybe 5 or 6 open wind collecting spiral splines like a nautilus shell, only in a circle. It creates and funnels the wind to the ever narrowing center thru a venturi and then out the other side in a ever widening exit. The center will have a vertical opening with a vertical, cupped bladed turbine, that is off set to only pickup the cupped blades as it passes thru the venturi into the widening exit end of the dome. Wind would be caught no matter what direction it came from. The top of the dome would also be like air plane wing, speeding up the wind through the system. I have another generating concept using constant ocean currents and underwater sails. Looking for people that make things happen. Probably have disclosed to much! Lets hear it from you guys.

Well dear friend, there ain't no magical guys who will step in & perfect your idea/s- it is up to you & every other inventor- prove concept & then look for expertise to perfect/ commercialise your prototype.

BAHRAIN WORLD TRADE CENTER

"The building is a sail shaped building, twin towers, it faces directly onto the prevailing wind and the building uses the wind and it draws the wind onto the turbines, it speeds the wind up as it hits the turbines it also distributes the wind vertically in an equal way so the velocities are the same for each turbine and it also manages to really carve the wind up so that irrespective of wind direction up to 60 degrees off the horizontal, it manages to bring the winds directly onto the turbines, so that they're hitting the turbine at a right angle."

http://www.inhabitat.com/2007/03/28/bahrain-world-trade-center-has-wind-turbines/

http://www.ameinfo.com/73268.html

http://en.wikipedia.org/wiki/Bahrain_World_Trade_Center

http://www.theworld.org/?q=node/18504&answer=true

Hello inhenyero,

I notice the blades are well before the venturi so the pressure will be higher on the front of the blades and the low pressure from the venturi should draw from the back of the blades.

Brad

hello UV,

actually sir, i'm not familiar with the design of wind turbine. i just like to inform our friends that the idea of placing large funnels in front of a wind turbine already exist/applied in bahrain. this was designed & constructed by WS ATKINS. as far as i know, the shape of the building and the design of the blades solved all the questions raised during the discussion especially the wind direction. the construction of this structure was shown on the television program NATIONA GEOGRAPHIC.

good day!

RRCA

Not exactly a funnel...more like vanes...but where the wind is what moves (about stationary vanes...the towers) and must accelerate due to wind shear around the building(s)...which is a different principle than funnelling some wind through a conical shape. But similar to my previous question: why not attach the funnels to the turbine sails?

Thank you all for your input.

Hi again, Neil, I do understand that I need to develop the concept further for funding etc. I was hoping for some input on why the concept would not work. But maybe I did not describe a mental image of the idea. I will try to paint a better picture--I'll never be a tech writer. The measurements are just numbers for proportions. Take a 180 foot smooth round domed structure that has a curved roof line, lets say with a 40 foot elevated center. Now lets say there are six 20 foot arched portal openings around the outside base that funnels all the wind to the center and then out the other side as it widens out again. Regardless what direction the wind is blowing it would just inter and exit different portals making it a fixed system. A vertical bladed turbine would be located in the center. The portal walls would be lined up to funnel the wind only to half of the vertical turbine cupped blades. I think rather than just straight walls narrowing (funneling) to the center, the walls would be curved or spiral in like the lines in a nautilus shell or the lens of a camera and would have less resistance. I think the wind blowing over the dome will act like a airplane wing and pull the air though the portal exits. Any thoughts on the concept?? Knowing the the cost to build the structure, the turbine design, gearing etc. is another story. Hill tops, I would guess to be the best locations but flat midwest ground could work. So the funnel/venturi effect with a system like this could mean more energy can be taken out of a given wind speed when compared to our bladed tower turbines. Punch some holes in this idea. What do you guys think? If anyone could direct me to the instructions to post a picture this would be so much easier. Thanks

The idea would work. The problem is most people say wind turbines are enough of a impact because their size. If you want a better idea, instead of putting a huge manmade funnel (increasing cost dramatically, the eyesore, and environmental impact of being huge for the little output) look towards SYNERGY. Here's an idea, make the funnel effect with environment (already done), but by planting bamboo forests in rows (or other tall/tight plant growths). This would increase output, and increase plant growth and the bamboo could be harvested for all these new bamboo materials that are the hub-bub. Put the dang things in some thing tree farm and developers won't be able to buy the land cause it is used to make power and products (the land will still be put to use unlike the billions spent on Parks that do nothing but provide nature a place to barely hold on and people to enjoy it while it lasts). You get more nature and more power. This would not only increase parks (if economical enough), but could fund itself instead of taking taxdollars. Maybe even genetically engineer faster growing seqouias for a more dramatic funnel effect. The things will cut up birds, but those could be cooked and made into some delicious stew. Yummy yummy. Keep connecting pieces so the idea scratches everybodies back and it becomes a reality.

Great ideas Guest. Use Nature as the funnel.

Here's mine. You know the type of generation that relies more on small movement/lots of power? Tidal floats moving arms that pump fluid through turbines for example. What if we had a huge sail driven by the wind, and a cable attached to it pulling on a lever, small movement, but lots of power. A huge sail would need to be well anchored, and boy would the neighbours complain. Unless it was one of your trees.

Jim

Sir;

Try to compute your design using the MACH STEM EFFECT.This phenomenon might useful for wind turbine design.In summary,Mach Stem Effect states that wind doesnt' loss its velocity as it hits an object,as it deflects to other direction ,the wind velocity simply adds up to its previous velocity,thereby doubling or increasing its velocity,just like the design of twin towers w/ turbine in bahrain.See also nuclear blast effect,it will confirm the phenomenon.Thanks.

Mac5777,

The idea seems very feasible for capturing wind no matter what direction it is blowing. However, in order for each opening to be an efficient source of energy for the turbine, then they could not also act as an efficient exhaust. In fact, they would need to be angled and shaped such that the non-active entries did not allow air pressure to escape and rob from the energy being supplied by the active or partially active openings. You would need openings on the leeward side of the turbine to carry away the exhaust from the turbine blades.

Also, if this is a remote location from where the power will be used, consider the voltage drop along that distance as well when designing the generating capabilities. If it is truly a source of constant wind, then there is some merit there.