Hi, I need to design a Shrouded Wind Turbine, possibly with the Immersed Boundary Method. Can anybody help me finding the best program?

Thanks

Hi,

I don't know what the immersed boundary method is, but shrouded wind turbines don't work. The flow will simply go around it.

Regards,

Gerrit

Hi,

See H.Grassmann-CFD modeling for wind turbines at the page http://www.cd-adapco.com/press_room/..._turbines.html

nice piece of information, now it is Gerrit turn to explain his posting

I know these CFD computations and many many more similar computations. It has been proven by Betz in the 20's that no CFD is ncessary to prove that this doesn't work. It's just the energy conservation law of thermodynamics that says enough.

First of all in the link they say that the prototype didn't work, amazing while CFD did, isn't it? Then they say, "we adapted the geometry and now it works." Again it works only in CFD, there's no prototype working.

A shroud works well for a turbine engine, where you use energy to keep it moving, however if you EXTRACT energy you won't be able to extract more energy than there's available in the wind, would you? Probably this simulation has a source of extra fake energy caused by wrong boundary conditions.

Betz, shows it very clearly, Power = Force * velocity Okay, I could brake the wind completely and have a lot of force, but that wouldn't move my blades, result: Force = maximum, velocity=0, => power=0. I also could let the rotor rotate freely without braking it with an energy extractor like an electronic generator, result: No force to be extracted (only friction) and a maximum velocity, again POWER = 0.

Betz shows with energy equations that there's an equilibrium in this which gives you exactly that force and that velocity where the power = force*velocity is at its maximum. This is called the Betz limit in wind energy and it's impossible to exceed that limit Every amount of wind energy that you want to squeeze in the rotor in order to extract more will COST you more energy to move the wind at first.

Once again, if the wind "sees" the shroud it will go around it. This again shows the reliability of CFD, there are to many people believing this.

Gerrit

You are spot on, you cannot obtain more power than betz theory (59.3%) predicts. However, although a shrouded wind turbine is not effective, diffusers (a downstream shroud) have been shown to make wind turbines a bit more efficient. They do, however, result increased windage on the whole wind turbine structure.

http://www.ifb.uni-stuttgart.de/~doerner/diffuser.html

James

Hi again,

Thanks for the link James, I'll read it with interest.

A question that we've not been asking us here and that has nothing to do with aerodynamics is, is the energy gain (assuming that one of the shrouded configurations work) worth all the effort?

Finally you want to design a turbine that gives you a competitive cost of energy, euros/kW. A shroud around a turbine is so inmensly expensive that its costs don't compensate for its extra energy gain (if any), because of the higher costs, you would need much more years before the machine starts producing you money.

You'll also have a much bigger influence of yaw misalignments etc. This makes it, apart from the fact that it's aerdynamically disputable, economically not profitable.

James, Interesting. Has there been any success with "winglets" or other devices which enhance aircraft efficiency, or do they simply not have the same level of improvement at the wing loads which wind turbines operate at? -Andy R

Yes, there have been, but not as succesfull as for aircraft, nevertheless, the performance improved because of less tip losses.

To finish this discussion of maximum performance, it is important to emphasise that CP is, strictly, not an efficiency, so that the Lanchester-Betz limit is not a limit on efficiency. Hopefully, the discussion in Section 1.1 of the amount of wind passing through the blades emphasises this point; improved performance only requires an increase in the amount of wind captured by the blades that outweighs any degradation in efficiency of conversion. Several methods have been proposed to increase flow capture, of which "diffuser augmentation" is probably the most promising. A "diffuser augmented wind turbine" (DAWT) has a diffuser installed downstream of the blades (and sometimes a concentrator upstream) to force the wake to expand more rapidly than it would otherwise. This increases the air flow through the blades. It is easy to design a DAWT whose performance exceeds the Lanchester-Betz limit. It is, however, generally thought that the structural and other problems of DAWTs, such as the difficulty in responding to changes in the wind direction, make them unsuitable

The preceding paragraph is taken from the freely available notes on wind turbines by David Woods Equation 2.17) http://www.wind.newcastle.edu.au/notes.html

"It is easy to design a DAWT whose performance exceeds the Lanchester-Betz limit"

Luckily they're not your words Ahmed.

It's impossible to exceed the Lanchester-Betz limit as it is equally impossible to build a perpetuum mobile.

There are some recent experimental results for ducted turbines that may be of interest to this debate. See: http://www.cyberiad.net/tide.htm

Leo.

Modern science is based on natural/experimental facts -> observations -> deductions Gerrit, this is not a personal debate, Where are the facts that support your claims? Thanks Leo

Don't worry Ahmed, I didn't take anything personal, I like this forum and hope you don't take anything personal either, but I am not going to answer any longer to this issue, hope no one gets angry.

In the link they say: "The turbine was tested by mounting it in front of a motorised barge"

Once again, MOTORISED, you are giving energy to the system. This energy is being used to press more water into the turbine blades, if you would only extract energy, the concept doesn't work anymore. At least as far as I know.

If there's an "extract only" system as an example, I'll admit that I am wrong, but it seems to early for that

I wonder who of you really read Betz' derivation.

Best Regards,

Gerrit

Interesting! The boundary condition in CFD can be improved to be more robust and act more like the natural real wind. Pumping wind into the CFD domain by using over-simplistic artifical method as in some CFD will disable diversion of wind flow away from the high pressure region such as a region of a shrouded wind turbine. There must be a good balance/equilibrium at which the critical pressure at the region of the wind turbine does not divert windflow away from it. I tend to agree with Gerrit.

A subroutine can be developed for the inlet of a CFD domain in a wind turbine case which takes into account the critical pressure of wind turbine region (at which point windflow will divert, due to pressure increase at that local region as opposed to massively abundant lower pressure region hundreds of meters away from and above that wind turbine location). The path of least resistance.

I am the inventor of a wind power system using static airfoils. This is a one in a lifetime proposal that may solve our energy problems.The challenge is to demonstrate that wind power is the way forward. I hope to make contact with someone in the CDF community that may be interested in this project.

The CDF application would require modeling of multi element airfoils.

I envision these twin slender skyscrapers sited onshore and used as both habitable structures and power generating towers. They would have a kidney shape and produce 50 MW of power. These slender towers would not be ugly and will use 1/10 the land needed by horizontal turbines.

I have discovered a means of producing electric power from the wind that is many times more efficient then the horizontal turbines now in use. My patent pending wind machine will power the 21 st. Century! Imagine a 50 MW wind power plant that is operational 100% of the time. The cost of wind electric energy must be reduced to below $.03/ kWh. and made more reliable in order for wind power to become competitive with coal. My discovery is an innovative machine using static airfoils.

Rotors produce power proportional to the diameter squared. My patent pending invention produces power from the wind not by increasing rotor diameter to immense sizes but by increasing the wind velocity, and since power is proportional to the cube of the velocity you immediately see the advantage.

I am interested in a CDF study of my concept. Is there some one on this blog that can help me.

Shrouded turbines respect Betz Theory, because the theory is based upon the mass flow.

Increasing mass flow, maximum power will also increase, this is the reason why a bigger turbine produces much power of a smaller one. When you add the diffuser, you increase the mass flow, so the Betz limit rise. You are not going over the limit, you are only rising it.

Shrouded rotors produce much power than conventional ones, but the "distance" from Betz limit is almost the same. Instead of building a bigger rotor, you can add a diffuser, I admit that building a big shrouded turbine is very expensive, but it's the best choice if you have to build a small turbine.

Read "Wind Energy In the Built Environment" by Sander Mertens.

Please send me an email describing in detail your design intent. Maybe I can help. Email azmir_isa@yahoo.com

Could you please provide your patent number so we might review yoyr concept? Cheers