In recent days Iv'e found myself wondering why wind turbines of a ducted variety haven't been developed. Seems to me that a ducted turbine disc or fan, following a flow enhancing stator might prove effiecient for marginal wind conditions. ther could also be a benefit from "stuffing" wind into the inlet via area rule. I thought this section of the forum might be the place to find some input on the idea anyways.

Short answer: higher aspect ratio's are more efficient at lift generation.

So stator's enhancing airflow or wind into the wind turbine would not help? I'm thinking in terms of a modest sized turbine, maybe 10' dia for private use. Six stators ahead of a 5 bladed fan.

I have wondered about this myself.
It would be an interesting experiment to do in a small scale (1 meter) or so to see what type of results you get. I have often wondered if the venturi effect could be brought into play with this type of a wind turbine. While a high aspect is the most efficient lift generation for an airplane riding on air does that mean that it is the only way to harness the wind for other purposes? I wonder what the trade offs would be. If you look at standard power generating systems that use steam they use turbine to drives the generators. Now I understand that the shorter multi-blade turbine can operate at much higher RPM's but it must also be more effective at being a power exchanger as well with larger amount of surface area. It may well be because a turbine is not as efficient over a wide range of speeds, and does not come into its range till it is really turning fast.

cost

As with anything that has to turn a profit, cost matters.

The structure to support the monster costs money. Probably more than the duct would. And then add up the cost of the support structure and the duct, and with that amount (not even including the fan), you could probably build 3 or more fan-only installations.

Well cost isn't too much of factor, I'll be building them myself. I would like to keep computer-control out of it as much as possible by using balanced for optimum performane stators. The theory of which relies on airfoil shape and pivot point I sappose. As for the fan, or turbine end that will likley be a one piece composite part (remember 10ft. dia.). Try to imagine a ducted fan on a stick catching wind to light an led bulb.

I'm sure that money dominates all designs. Right now, it costs about a million dollars for each megawatt of capacity for the commerical systems. Small hobbiest systems cost more per watt.

Inspite of the high initial costs, wind power does come pretty close to being cost effective. Biggest problems is the best wind is usually far from population centers, and that most systems are only producing prime power 30% of the time. So energy storage is a problem. One possible method would be using the electricity to produce NH3 which is stored at very low pressure as a liquid, yet has about 50% more Hydrogen storage than pure liquid H2 by volume. And the amount of energy it takes to make liquid hydrogen consumes a huge percentage of power.

Solar thermal may be a much better method of energy production, especially in the SouthWest part of the country. The energy can be stored in the form of molten salts (thus able to produce power 24-7). The rest is simple Thermodynamics.

I know that right now a 20KW system runs around 50K for the components. This is just for the components a three bladed turbine/generator, 150 foot tower, and inverter the basic parts only if you are on the grid now. The cost of assembly would be probably at least 10k on top of that (cement base, crane to hoist the tower and turbine). So all told around $60,000 for the system ready to go, or roughly $3 per watt. Like High Planes says a good rule of thumb is that you will be producing power about 30% of the time so best case is you will reduce your bill by that 30%. Depending on your location and the surrounding terrain you may do better or worst than that.
I have and am still thinking about doing a wind system, because I am close to the coast and in a prime area for wind power. I will also be able to negate the storage system where I will just back feed the grid when the system is producing more than I am using.
I had not really thought of the change state salts (that are popular with solar systems) as a storage medium but that to is a great idea. I have had solar collectors (thermal) since 1978 (for hot water), and they still produce today, other than replacing the exchanger and storage tank a couple of times I have had no problems with them.
Wind power is a great idea but a lot of work but like others have said it is pretty cost effective. Bottom line is how much it cost to what you will get out of it.
Here are a link for info on wind:
http://www.windturbine.net/wind_industry_links.htm

So about the stators ahead of the turbine fan?

should I venture into this for my senior seminar topic?

The only thing stators do is straighten the flow. Perhaps you are thinking of a venturi.

I'd think of changing majors, to something in engineering.

You would need a series of stators and impellers(fans) enclosed within a duct,with one honking huge venturi in front of it.
You would also need to have a speed control to limit over speed (transmission to generator).
With blades they use pitch to control speed, I do not think this would work with the impeller.
Perhaps some form of hydraulics would work for speed control, using a hydraulic pump with a pressure regulator driving a hydraulic motor that in turn spins the generator.


Just a few things to keep mind whatever you build:
It will have to be at least 20-50 ft above any nearby obstacles (buildings, trees, hills). So the weight of your wind turbine is going to be pretty high up in the air for it to work.
With the mass of your intake, turbine duct, turbine, generator up 50 or more feet up in the air you will need one beefy tower as well.
Being able to service it in a safe manner is a must also. You are not going to be able to raise it and lower it every time it needs service so you need to build some sort of platform and locking system for the pivot as well.
Then you have to deal with the electrical system and storage/or connection to the grid (inverter/sync).

Cratecruncher hit the nail on the head. To get the most work out of the wind size matters. Long high aspect ratio blades do two things that relatively short turbine blades cannot. First you can put a lot more area into the blades compared to the shorter ducted fan style. Second the leverage arm to turn the turbine is much longer so the mechanical advantage is far higher.

Finally there's the fact that even with a really big inlet into a venturi before the focused air hits the turbine there's only so much pressure boost you'll get at the turbine before the venturi packs up and won't let more air into the mouth. This is all related to airspeed and the size of the venturi. But at some point if you can't FLOW the air fast enough the venturi will pack up and stall and there'll be an "ice cream scoop" of stagnant or slow moving air stuck in the mouth of the venturi that will ruin the velocity rise. At that point the air will tend to flow around the sides of the higher pressure "plug" and around the sides of the venturi instead of working harder to cram air into the venturi mouth.

Venturis work best when there's a source of suction in the narrow outlet rather than a resistance that needs to be worked on. Mostly a venturi is a flow smoothening device moreso than a pressure modification device. Yes it DOES do both but mostly it's about avoiding stagnant bubbles choking off the flow at the mouth of a airflow opening.

actually engineering is physics...I'm doing applied physics too so it's all the pre engineering classes... So basically I'll present myself as an engineer when I graduate

Understanding physics is like peeling an onion, below each level of generalization, is a deeper more complex world of greater nuance and knowledge. Offshoots of physics are applied sciences more commonly known as engineering disciplines such as electrical engineering or mechanical engineering. Subsets of these disciplines include areas of expertise like control theory or fluid dynamics. All are quantifiable with what is known and yet unknown.

Why don't most gas turbine and turbofan engines have a leading row of stators??????

Because there's no spiralling airflow to straighten up until they get past the first compressor fan.

Actually, with most gas turbines, once you are past the fan and entering the core engine, there is a row of inlet guide vanes before the first compressor stage. In many turbines these IGV's are also adjustable and vary with compressor speed. Their job is to present the air at a suitable angle to the first compressor stage (a 'stage' being a rotating set of blades and a stationary set of vanes), this angle to ensure that the angle between the flow and the rotating blade is held below the stalling angle of the blades. As the speed and flow is variable, then the guide vanes (and often the stationary vanes too, known as Variable Stator Vanes, VSV's) modulate within a set of parameters to maintain flow through the compressor. So it could be said that these IGV's set up a spiral airflow for the compressor. Of course the blades then spiral the air the other way, the next stator back again, etc. The net flow is almost straight.
Evan, WB #12

Wow, thanks Pimmnz for awhile there I was thinking that all on my own. Why wouldn't a set of flow optimizing stators or guide vanes enhance flow into a wind turbine?

Because anything in the entry will only reduce the flow, vanes have volume, and that means less air through the entry. If you want the wind to blow your turbine around, then long, thin blades are the way to go. It may be that a ring around the tips of the long, thin blades could help, but as tip losses from a blade being driven by the air is likely to be negligible, again it would be of dubious value.
Evan, WB #12.

I know this is a little off subject but there is something I have wondered about. When an aircraft becomes trans-sonic, what is happening inside the turbine? Are conditions trans-sonic in there too? What's going on at the intake with the shock waves bouncing around?

In any aircraft capable of supersonic flight the inlet ducts are deliberately designed to introduce a shockwave, or a series of shockwaves, to reduce the inlet air speed to subsonic. In any gas turbine the flow through the engine is well below sonic speeds, if you see a blade section, thin and undercambered, you will understand why this is necessary.
Evan.

There's another very good reason why ducted fans are not used. I mentioned it before but no one seems to have considered it.

Ducts tend to pack up and limit flow pretty quickly. Things like venturi intakes and similar ducted shapes only work because the vanes in the duct or the crankcase on the other side of the carbeuretor are powered up and are drawing air INTO the duct in an aggresive manner. In these cases the venturi shaped intakes smoothen and permit more airflow. But if you want to rely on the air being rammed in and using the pressure and velocity to turn a fan then that's a whole other issue. Such an arrangement could perhaps be made to work but it would require a far, far larger venturi mouth compared to the fan diameter to allow the mass of the wind to force the air into the fan. Testing would be needed but I can assure you that it would not look like an overgrown intake stack for a dragster. Instead we're probably talking about a mouth diameter that is 4 to 8 times the diameter of the fan throat to achieve a good enough "compression" to drive the fan. Even then I'm not sure the efficiency would be there compared to an open propeller blade that is the same size of the mouth of this duct.

The venturi mouth would probably be closer to 10-15 times the size of the Ducted Fan. Bruce I think you are right it would not look like the stacks on a dragster, but rather the elongated shape of a wind sock, it would have to be long to allow for the pressure needed to spin the fan. The venturi for this setup would look a lot like the old microwave horn antennas used for satellite systems years ago. The size and mass of the system is going to be the down side I think. Then again to make something that will work in wind anywhere from 3-5 mph up to 70mph is going to require a lot of work as well.
If you want to try an experiment take a hyperflow ducted fan unit with the brushed motor it come with and use that for a test, it is around 3 inches which is 1/12 the size mentioned my the OP. Set it up with a venturi so that it will produce 8 volts at 400ma load in a 3 mph wind (then increase the load so you are producing 10 amps) and that will give you the size and proportions needed for your inlet concentrator system. After you set it up to work in the 3 mph wind, try to use it in a 30 mph wind it will blow apart unless you have some sort of pressure bleed system, so you do not over speed you turbine/generator. The problem of wind power is that the wind is not constant or at a set speed and this is something you have to take into account, as well as storms when the sky is the limit. I have no doubt that something could be made to work it is just that it would be a massive, complex system , that need to be mounted on a tower high enough to clear obstacles and turbulence.
As I mentioned before I had though about something like this myself, but the logistics of making it work made me shy away from trying it.[sm=75_75.gif]

I have included a sketch of what I was thinking.[8D]
One of the draw backs was the size.
Thinking of putting something the size of Ames's wind tunnel several hundred feet in the air for a commercial scale. Or in the case of a 1 meter unit the size of a semi trailer a couple hundred feet up in the air.[sm=72_72.gif]
Now this has got to be able to be put up in the air so it is not a threat.[sm=50_50.gif]
This has to be able to take winds upward of 200mph do to the hurricane threat in this area or where strong storm winds may be encountered.
The strength tower is an issue to be able to withstand the wind loading of the turbine assembly.
Now the mass of the shrouded assembly for the turbine has to pivot and be able to support itself up on the tower.
Like I said lots to consider without mentioning one other thing no one has brought up.
The noise…
What happens when you move air past a enclosed fan?
I know I would get some noise from my wife and neighbors about what it sounded like.