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Old 09-26-10, 08:58 PM   #11
Sularus65
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The purpose of a longer/skinner airfoil over a shorter/fatter one is torque. The long the fulcrum, the more leverage it applies. Those large wind turbines are not designed to travel at high speed. In fact, in high winds they usualy furl the blades to let the wind pass without turning the blades.
A design such as the one above is for a high-rpm application. I have spent over 11 years working on jet engines and have seen more than a few designs. The smaller blades each grab a larger portion of air. The shroud and the bullet nose help channel and keep air in the blades. I venturi would be useful in so much as it will speed up the air as it approaches the blades to increase its speed. At the same time you need a divergent zone behind the the blades before exiting the shroud. The divergent zone will increase pressure to help prevent backflow and slowing down the turbine. Hope this helps clarify some stuff.

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Old 09-27-10, 07:06 AM   #12
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I'm not a windmill expert altho I've done a lot of reading on it recently. My impression of the small wind field is that its full of charlatans and entrenched opinions the deepest trenches being inhabited by Hawters.One expert (altho admittedly he seems to be a bit of a hawter ) , who has IMO posted some sensible stuff on this site is B. Mcgovern who says of the myriad small Hawts "What a poor lot they are ". I tend to agree altho some of the newer Hawts and Vawt ideas seem pretty good'
All I will say is that when I started out in electronics we thought Bell telephone labs consulted God directly but MIT were one better in that God consulted them. when in Boston a couple of years back I made a pilgrimage to MIT and was interested to see they had a helicopter landing pad marked H and a smaller one beside it marked G. Draw your own conclusions, but if MIT are involved in the design and not just the measuring this is probably good for some of the claims. As I say I'm not an expert but if the best way to extract wind energy finally proves to be up to 80 metre diameter slowly rotating propellers I ,for one , will be staggered.Staggered but not surprised , observing what has happened to technical education in the UK in the last 40 years. However that's another rant. Big Al.
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Old 09-27-10, 10:59 AM   #13
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Being retired I have a bit of reading time and have read the other posts on this subject. All I can say is I'm staggered (not you will have gathered a rare event , and its not always alcohol.. Consider wind tunnel technology ,been around a long while and as it's prime users are the military and civil aircraft manufacturers there's not much room for b---s --t in the technology. The discerning may recognise that getting a large volume of air to move fast by inputting energy is not that dissimilar to extracting power from fast moving streams of air. Imagine the scene. The buyer of wind tunnels awaits the arrival of the wind tunnel sales reps. Next! "we've got a great tunnel with the most efficient fan -a single blader !!! "Next -we'll call you" without spelling it out in detail the posts on this thread in the main seem to be coming from deep trenches.Sularus 65 seems on the trail and not in a trench ,however. Big Al

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Old 09-27-10, 01:50 PM   #14
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Being in a trench doesn't mean you're wrong. Once you have gone through all the iterations you can possibly think of, perhaps you will come to the same conclusions. Carry on.
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Old 09-27-10, 04:48 PM   #15
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Hey we are all here to help each other, at least I hope so. Big Al was just illustrating that most people tend to either agree with each other or disagree without any new thought being generated. Researching the ideas involved and/or finding someone with prior knowledge helps in expanding the ideas of those around, which leads to the generation of new thought in everyone.
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Old 09-28-10, 01:18 AM   #16
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and my apologies for letting a bit of sarcasm sneak in. The point I was trying to make (not very well ) was that fans , propellors , turbines all have the same basic problem of trying to couple mechanical movement to fluid movement and what works fluid- to- mechanics ought to work mechanics-- to- fluid.Or does it ??? Sounds like we need one of those philosopher /mathematicians to answer that . The sort of guy who can tell me if Bett's law can be broken by a wind turbine blade that almost reverses the flow ( a la Pelton wheel ). Its probably not relevant to wind but I believe Peltons , working with a nice chunky fluid like water , achieve efficiencies in the nineties.
I agree that the maths at first make the jet turbine claim to be the equivalent of a normal turbine twice the diameter seem impossible but if the vortex produced at the back of the jet turbine sucks in flow that would normally pass the turbine--hey who knows ?? Maybe not twice the diameter but maybe part way there.
Anyway I think it looks awful nice , the sort of turbine one could take home to your mother.

Last edited by Big Al; 09-28-10 at 01:25 AM.. Reason: Just an addition
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Old 09-28-10, 07:27 AM   #17
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To me the bottom-line question for all these jet-turbine and similar ideas is: Why? Why do we care if it only takes up 1/2 the space? Are we short on space? No. At least not yet. So the limiting factor then becomes one of cost. Is it cost-effective? If it can be made for the same or lower price than a conventional turbine then it has some merit. But why pay more just to save a little space? OK, there might be some application in limited-space situations like rooftops in cities. But these have been proven to be poor locations for wind turbines anyway - not likely to be productive enough to pay for themselves. So probably no benefit there. But if there were, you could only place so many of these on the roof before they started to shade each other and the output of all of them would decrease.

I am sceptical of their claim of 40% lower cost. There is a lot of material in those shrouds and the blades probably need to be relatively precisely made. I would be very surprised if the retail cost of these was less than a conventional turbine.
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Old 09-28-10, 09:49 AM   #18
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I agree somewhat patrick, but do we have to wait until we run out of space before we begin making units that are efficient and smaller than some larger ones. There is no reason we cannot work on both and achieve optimal results.
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Old 09-29-10, 11:42 AM   #19
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May be repeat-think I forgot to press send b4. well we're a bit short of space in the UK and two of the powers in wind Netherlands and Denmark are n't too spacious either. Even in the Us ,OZ and NZ a single lorry must be a bit greener than the fleets of carrying and lifting vehicles u need to erect the current crop of megawatt windmills with diameters now approaching or exceeding soccer pitch lengths.
As u know I'm a sneaky Vawt fan , and I believe you can get 10 times as many vawts in the same space as hawts (if you place them carefully so the vortices are taken advantage of ). Much as I hate praising a hawt I suspect these could be packed pretty closely too.
Anyway I still think its a fine looking turbine and hopefully pretty forward thinking too IF it lives up to the claims in the article. Rgds and thanks for forwarding Vawt reference on Darreus turbines. I'm still plugging away and now have a power predictor erected which given a couple of months logging wind will pave the way I hope to my Megawatt Vawt in a shoebox. I must admit I shall also need my $25m series B funding and come to think of it I don't remember getting my series A funding. Big Al
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Old 09-29-10, 01:53 PM   #20
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I was on looking at these generators further yesterday and just by looking at them it appears they are heavily based on jet engines. They appear to have all the requirements I discussed earlier. A gradual convergent zone before and directly after the blades. Immediately after the aft convergent zone (behind the blades) there is a large divergent zone (where the two different diameter shrouds are). This will create the high pressure area which will prevent backflow, which will slow the blades down. The only thing I can ascertain from the illustrations that can be improved is the shape of the blades. I had seen some photos of a new generation of compressor blades which result in higher efficiency numbers for jet engines. I am not sure if these blades will work the same way in this instance, but it couldn't hurt. The only problem is I can't remember where I saw them. I have been trying to find it again, if I do, I will post them up for all to see.

J

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