New type of wind powered generator - would it work?

[jammy_basturd]

OK, so I have a very rudimentary grasp of physics, plus it's quite late.

However, we know that fluids and gases speed up as the passage narrows (I'm thinking the current of a river through a wide part compared with a narrow part).

So, could you not put a wind turbine at the end of a very large, gramophone shaped funnel? As the wind enters the large opening at one end it speeds up and speeds up until it gets to the small, narrow end, hitting the wind turbine at a much greater speed, thus turning it with more force and generating more electricity?



I'm going to guess why it won't work... something to do with the conservation of energy and that the force is concentrated in a much smaller area, so the overall turning force is unchanged, it's just concentrated on one small spot? Or maybe I've just solved the renewable energy conundrum.

[Steffan]

jammy_basturd said:

OK, so I have a very rudimentary grasp of physics, plus it's quite late.

However, we know that fluids and gases speed up as the passage narrows (I'm thinking the current of a river through a wide part compared with a narrow part).

So, could you not put a wind turbine at the end of a very large, gramophone shaped funnel? As the wind enters the large opening at one end it speeds up and speeds up until it gets to the small, narrow end, hitting the wind turbine at a much greater speed, thus turning it with more force and generating more electricity?

I'm going to guess why it won't work... something to do with the conservation of energy and that the force is concentrated in a much smaller area, so the overall turning force is unchanged, it's just concentrated on one small spot? Or maybe I've just solved the renewable energy conundrum.

Three obvious downsides.

1) Cost: It would be a huge unit subject to permanent weather and buffeting etc, Bound to be expensive

2) Losses: In the device with friction etc would reduce any gains. As you suspected.

3) Inherent inefficiency: It does nothing to address the dead periods that plague wind all generators As you expected I think.

[Simpo Two]

jammy_basturd said:

the force is concentrated in a much smaller area, so the overall turning force is unchanged, it's just concentrated on one small spot?

I suspect this. There is only so much energy in the air, you're just concentrating it.

[mrmr96]

How would you keep the gramerphone pointed into the wind?

[CrutyRammers]

Simpo Two said:

jammy_basturd said:

the force is concentrated in a much smaller area, so the overall turning force is unchanged, it's just concentrated on one small spot?

I suspect this. There is only so much energy in the air, you're just concentrating it.

I'd go with that. You're stretching it - it goes faster, but at lower pressure. I can't remember exactly how it works, but I think that the mass air flow will be the same outside as inside the funnel, and that's what would drive the turbine.

[jammy_basturd]

Steffan said:

Three obvious downsides.

1) Cost: It would be a huge unit subject to permanent weather and buffeting etc, Bound to be expensive

2) Losses: In the device with friction etc would reduce any gains. As you suspected.

3) Inherent inefficiency: It does nothing to address the dead periods that plague wind all generators As you expected I think.

Don't existing wind turbines have problems with 2 and 3? So it could possibly be an improvement on what already exists?

mrmr96 said:

How would you keep the gramerphone pointed into the wind?

Well I didn't envisage actually putting a gramophone shaped funnel in front of existing wind turbines. I thought that perhaps these installations could be built on top of hills facing all directions and that the generators would be underground - which should make them less sightly.

Simpo Two said:

I suspect this. There is only so much energy in the air, you're just concentrating it.

Hmmmm. I did think however, that with existing wind turbines, they can only take advantage of the area of wind that is equal to the area of the surface of the blades. Whereas in theory, with this design you could take advantage of more than that. Plus could I not take advantage of the same science that is at play with the new Dyson "Air Multiplier" fan?

[anonymous-user]

What you are talking about is, in effect, virtual "gearing" for wind turbines. Take a large volume of slow moving air, and turn it into a smaller volume of faster moving air. Except, simply optimising the blade design of a wind turbine already does exactly that! When a turbine site is chosen, the mean, min & max wind speeds are measured or calculated, and the blades chosen for the generators (and the gearbox ratio in fact between the blades and the generator. It's a compromise, between spinning the generator in the lowest possible wind, but not overspeeding the system in the strongest possible wind.

Aerodynamic design of the main blades is hugely advanced now, with extensive CFD and stress analysis being done to optimise the span, chord and profile of the blade, and lots of materials work to make it as light and strong as necessary for the resulting design.

Because wind power is so distributed, it's generally always better to just install another turbine than try to fully optimise the one you already have, especially if that optimisation costs a lot of money (like a massive horn/funnel assembly would ;-)

[AER]

It's more than that Max.

If you take the same volume flow of air, then pass it through a nozzle, of half the area, you'll double the flow velocity and have four times the power available to extract.

I've often wondered if you could cover an optimally-facing gully with a huge "tent" nozzle and have the turbine at ground level, apart from giving birds and bees a thrill, you'd make much more power from the same landform. Additionally, you'd increase the pressure ratio across the turbine by the addition of the lossy tent structure in the wind flow.

BTW, I have seen a video on Youtube of something like this idea operating at a back-yard scale, but I can't, for the life of me, find it right now.

[maffski]

AER said:

If you take the same volume flow of air, then pass it through a nozzle, of half the area, you'll double the flow velocity and have four times the power available to extract.

No, you have the same power, just in a smaller area - so you're trading large blades for small blades and this structure. The 'catchment area' is the same.

[jammy_basturd]

But the catchment area doesn't have to be the same.

I don't know real world values, but lets say that the blades of a current wind turbine have a surface area of 50m2. Those blades can only ever be turned by that amount of air.

Whereas if you can funnel the wind with a surface area of double that, and act on the same wind turbine then surely you can turn the blades at twice the speed - if you can accelerate the air that much?

[anonymous-user]

AER said:

If you take the same volume flow of air, then pass it through a nozzle, of half the area, you'll double the flow velocity and have four times the power available to extract.

The problem i think is getting the same mass flow at the exit of the nozzle? i.e. the velocity increase is driven by the pressure difference, where a higher upstream pressure exists (it must be higher, because the turbine must exhaust into ambient pressure downstream, and there must be a positive pressure ratio across the turbine to be able to extract power from the mass flow). As such, this higher pressure entry condition causes incoming air to simply slide sideways and around your nozzle. No matter how big you build your nozzle, it will always have a finite size, and compared to the turbulent and uncontrolled flow of wind, that size will be 'characteristically' small?

In effect, a cone of static air is going to form at the entrance to that nozzle, reducing the mass flow, and pressure recovery isn't it?? (i'm assuming that the size of this nozzle is sufficient to make boudary layer wall losses minimal)

[marshalla]

Ermm - I hate to take the wind from your sails, OP, but that's not a new idea.

From Feliks' posts on this thread : http://www.pistonheads.com/gassing/topic.asp?h=0&a...

we find : http://sheerwind.com/technology/how-does-it-work

[jammy_basturd]

marshalla said:

Ermm - I hate to take the wind from your sails, OP, but that's not a new idea.

From Feliks' posts on this thread : http://www.pistonheads.com/gassing/topic.asp?h=0&a...

we find : http://sheerwind.com/technology/how-does-it-work

Hey, cool! I wasn't worried about coming up with a new, original idea, but it's nice to know that "my" idea has been tested and shown to have some legs.

[AER]

Max_Torque said:

AER said:

If you take the same volume flow of air, then pass it through a nozzle, of half the area, you'll double the flow velocity and have four times the power available to extract.

The problem i think is getting the same mass flow at the exit of the nozzle? i.e. the velocity increase is driven by the pressure difference, where a higher upstream pressure exists (it must be higher, because the turbine must exhaust into ambient pressure downstream, and there must be a positive pressure ratio across the turbine to be able to extract power from the mass flow). As such, this higher pressure entry condition causes incoming air to simply slide sideways and around your nozzle. No matter how big you build your nozzle, it will always have a finite size, and compared to the turbulent and uncontrolled flow of wind, that size will be 'characteristically' small?

In effect, a cone of static air is going to form at the entrance to that nozzle, reducing the mass flow, and pressure recovery isn't it?? (i'm assuming that the size of this nozzle is sufficient to make boudary layer wall losses minimal)

I'd argue with the right geometry you'll increase the pressure differential across the nozzle since it's forming a flow-loss situation in the wind direction - i.e. you get no pressure recovery on the outside of the nozzle. At the exit of the nozzle you will have upstream pressure minus dynamic pressure (due to the increase in velocity) which will match the static downstream pressure (roughly speaking). This increased velocity will yield a lot more power (m_dot.v^2) but the bulkstream flow velocity downstream of the nozzle will be much lower (causing all sorts of nasty vorticies over the top of the nozzle structure, but who gives a shït.)

I think one of the key causes of low power outputs from unducted turbines is that the pressure ratio across them is piss-weak, so most of the wind energy is just carried downstream.

[98elise]

jammy_basturd said:

But the catchment area doesn't have to be the same.

I don't know real world values, but lets say that the blades of a current wind turbine have a surface area of 50m2. Those blades can only ever be turned by that amount of air.

Whereas if you can funnel the wind with a surface area of double that, and act on the same wind turbine then surely you can turn the blades at twice the speed - if you can accelerate the air that much?

I understand what you are saying, but from an engineering perspective its far better to just increase the blade area of the turbines (bigger blades, or more units)

A huge funnel would need to move, and would not be as efficient as a blade coveing the same area.

[Mojocvh]

http://www.windturbinesnow.com/wind-lens.htm

[paranoid airbag]

Although it doesn't quite answer your question, I think you'll find it quite useful anyway:

http://en.wikipedia.org/wiki/Betz%27_law

Essentially, you've got to get rid of the air that goes through your turbine - and that means leaving it with some kinetic energy. The less kinetic energy you leave, the smaller the turbine is going to have to be for a given area of downstream air - meaning upstream air is just going around the turbine, instead of through it. Conversely, the more upstream air your turbine captures for a given area of downstream air, the more kinetic energy it's going to have to leave. The handy thing is, this is pretty much independent of the details of how your turbine works.

[XM5ER]

Mojocvh said:

http://www.windturbinesnow.com/wind-lens.htm

Wow a website written by Kevin aged 10+1/2.

marshalla said:

Ermm - I hate to take the wind from your sails, OP, but that's not a new idea.

From Feliks' posts on this thread : http://www.pistonheads.com/gassing/topic.asp?h=0&a...

we find : http://sheerwind.com/technology/how-does-it-work

I like this idea though. Question is, if you can extract a significant portion of energy from the wind flow, what happens to the local environment in terms of reduced and/or redirected air movement?

Edited by XM5ER on Thursday 5th September 11:28

[205alive]

Your idea is clearly sound, as other have indicated and proven - the phenomenon you're describing is the venturi effect.

My take on power generation on the same principle is as follows:

Take a hollow cone shape and place a fan at the narrow end, connected to a dynamo of some sort.

Make multiple arrays of these cones.

Connect the output of the dynamos to some sort of feed in system.

Sink them into the fastest stretches of every river in the UK.

Everyone lives happily ever after, because let's face it, rivers never stop flowing...

The End.

Seriously, I come up with stuff like this all the time! Ask me the one about the retrofit device which... on second thoughts, that one could be a real money maker.