# Venturi wind turbines

Discussion in 'Electronic Design' started by [email protected], Feb 25, 2013.

3. ### Guest

It's freaking genius. I can see the EPA maybe requiring a 2-inch-square mesh to prevent hummingbirds from being caught in the draft, but... wow. Wow. And wow. US\$0.02/kw-hr, huh.

4. ### Guest

It does, but total air flow Q = velocity * cross-sectional area, similar I guess to how total power = voltage * current.

And, yeah, the cross sectional area at the generator is quite a bit smaller than at the intake.

Sure looks interesting though.

5. ### Guest

I can see it being less noisy and not so many complaints from
neighbors that
don't like their house and garden turned in to a blinking disco when
the sun is low

-Lasse

6. ### Guest

Ah, extractable power is more like 1/2 * (density of air) * (cross-sectional area) * (velocity^3).

http://uni-leipzig.de/~energy/ef/15.htm

I vaguely remember power is proportional to the cube of the velocity, and there are some really nasty equations we had to use/derive back in fluid mechanics classes, but this is a good distillation of the relevant equations (and quite elegant, I must add). No macroscopic mechanical energy balances required, haha.

Michael

7. ### Tim WilliamsGuest

Neato, and as obvious as hindsight makes it look, it's about time!

Seems to me it would suck rather than blow. If you do the old
blow-across-the-open-end-of-a-pipe trick, you get lift from the Bernoulli
effect. Specifically, the difference in wind velocity between ground
level (especially if you hide the intake within a dense forest or
something like that) and altitude causes a pressure difference

I suppose the catcher part is baffled and, perhaps, equipped with throttle
plates to shut off the non-windward sides, so only ram air travels
through. A passive structure would be possible with lightly sprung check
valves (air pressure might also provide the action), or perhaps simply
taking advantage of fluid flow (Coanda effect). If this is the case, it
leaves much of the head underutilized. I expect further improvements are
possible, and in development.

Tim

8. ### Guest

The website looks interesting, but it looks like they won't have product shipped until later this year...

http://sheerwind.com/

Minnesota... that's pretty close to you, Tim, right?

Michael

9. ### ArtemusGuest

I'm not an aero engineer but this looks like pie in the sky claims to me.
1. It appears that the intake area on this is significantly less than that of
a propeller style windmill. Therefore it can't extract the same amount
of wind energy. No?
2. There will be not insignificant loss of energy due to the aero drag on
the walls of the venturi. Compressing the air will also add to the losses.

There do appear to be some benefits, but efficiency isn't one of them.
Art

10. ### Tim WilliamsGuest

In a relative sense, yes. Digikey (Thief River Falls) ships practically
next day. But it's also a six hour drive.

For being mostly flat and midwestern, WI gets enough wind that they've
installed some turbines in various areas. As I recall there's a few
around the capitol.

Tim

11. ### Guest

The energy of the wind is directly proportional to the air density and
cross section area and relative to the third power of wind speed.

The cross section area can be the area covered by a conventional
horizontal axis wind turbine or the area covered by some vertical
construction or even the classical Savonius design.

If the structure shown in the picture is 30 m high and maybe 10 m
wide, the cross section area is only 900 m², why would anyone expect
it to generate 1.8 MW ? In a lossless system, that would require at
least 18 m/s wind, which is rare at 30 m above ground in most parts of
the world. The situation might be realistic a few hundred meters above
ground.

The basic flaw in arguing that a small structure would concentrate the
air into the turbine. The air is not "so stupid" that it would go
through the turbine, while it can more easily go around the
structure.

The situation is different, when the structure is kilometers wide
and/or hundreds of meters tall, e.g. a valley between two mountains or
when the air flow above a high hill, in which case the speed of air is
increased (compare this to the faster air flow above the wing of an
airplane).

12. ### amdxGuest

Hey Jeff, it does say they tested a 0.3 watt unit.

"The first small scale field unit, rated 300 mW was designed and
constructed last year and validated the CFD models predictions. A larger
scale field demo unit rated 1.5 kW to 5 kW also went live last year. "

I wonder if the pictures shown are the 1.5 kW unit mentioned above.

Mikek

13. ### tmGuest

Well there you go. Obozo will fund it if they kick some of the money back.

14. ### mikeGuest

"why is it so difficult to prove it?"

Build a uni-directional one out of plywood.
Bolt it to a flatbed truck, or on top of a bus.
Measure volume/pressure with speed as a parameter.
If you like the numbers, stick a generator in it.
Then go solve all those pesky issues with omnidirectional behavior.

If you can't make it work on a truck driving down the road at
2 or 20 or 60 MPH,
there's no need to pursue it further.

That'd be far more useful than a 300mW prototype.
And you could work on it where there's no wind.
And it'd cost far less and take less time than setting up their website.
But it'd garner fewer greedy/uninformed investors.

15. ### Guest

I do wonder about maintenance though. There's not much friction in clean, smooth PVC pipe, but in real life bugs are going to get sucked in, and those are going to leave sticky residues in the plumbing that will attract dirt, and next thing you know, the friction factor is way up...

Michael

16. ### Guest

Put the intake on a lazy susan, with a weather vane to point it into
the wind.

If you route or switch the exhaust similarly downwind (possibly even
through a reverse Venturi, for comic investor-suckering effect), you
can relieve some of the backpressure too. I dub it the double-synergy
Pushme-pullyou version.

Please send my checks to Emperor Oblahblah and her Moochelleness.
(Saves me the trouble.)
The double-stimulus version could propel the truck faster and faster
without limit. It uses the energy to print foodstamps on switchgrass
paper, with enviro-sustainable 200% economic return. Burn the
foodstamps in its bio-diesel hybrid hyper ion fuel-cell drive, and
you're on your way to wind-powered LEO.

17. ### tmGuest

Put the intake on a lazy susan, with a weather vane to point it into
the wind.

If you route or switch the exhaust similarly downwind (possibly even
through a reverse Venturi, for comic investor-suckering effect), you
can relieve some of the backpressure too. I dub it the double-synergy
Pushme-pullyou version.

Please send my checks to Emperor Oblahblah and her Moochelleness.
(Saves me the trouble.)
The double-stimulus version could propel the truck faster and faster
without limit. It uses the energy to print foodstamps on switchgrass
paper, with enviro-sustainable 200% economic return. Burn the
foodstamps in its bio-diesel hybrid hyper ion fuel-cell drive, and
you're on your way to wind-powered LEO.
--
Cheers,
James Arthur

+++++++++++++++++++++++++++++++++++

Oh, oh, oh... It's got the word "stimulus" in it. It simply can't lose. Just
think of the military uses for a LEO wind turbine. Hello, DARPA... hello?

18. ### rickmanGuest

The amount of energy a propeller style windmill can extract is limited
by the design constraints of a propeller. Consider that there is only
one place on the blade where it is moving through the air at the rate
that the wind is moving. Any location closer to the hub will be turning
more slowly pushing the blade faster and any place on the blade further
out will actually be moving faster than the wind, *pushing* the wind
faster and so slowing the blade. There is a term for this, but I don't
remember it. The blade tips are always resisting the motion of the blade.

I think it is theoretically possible to do better. In practice, I
believe the egg beater type blades are more efficient, but I'm not certain.

None of these propeller type designs are 100% efficient. If they were,
they would *stop* the wind, no? Then all that air would just pile up
and have to be shoveled away.

Compared to what?

19. ### rickmanGuest

Really? What do they do about buildings? Do they fold up in storms too?

20. ### rickmanGuest

I think it is funny that you guys think you are aeronautical engineers