Guide vanes (wind concentrators)

[lifer]

I want to build a large scale Lenz2 VAWT but due to architectural constraints I have to go short and wide (it will be mounted on a flat roof).
Due to technical limitations, I can't go too wide either. So I thought of using some (static) guide vanes to enlarge the swept area. It supposed to look something like that:



I've been in contact with Ed Lenz and he said it might be a feasible solution. Yet another advantage of guide vanes is to prevent blades of being back on the wind.

Anyway, I want to keep it simple so I guess two vanes on each side should be enough. Now comes the mystery: how to properly design/calculate those guide vanes? Angles, curvature, dimensions?

Does anyone have any suggestions? Thank you in advance for any tips.

[dnix71]

Those vanes as shown are blocking at least some of the wind no matter which way the wind comes from. I have a free concentrator. My AirX is behind the gap between two L shaped buildings that face the prevailing breezes. The arrangement looks like L J with the J being a backward L.

Unless your wind comes from one direction only you can't build a static concentrator for a HAWT. You need as large a swept area as you can do.

[lifer]

Those vanes are blocking the _unwanted_ wind, I believe. Like every Savonius derrived VAWT, there is an air-flow resistance encountered by the back of the wind turbine blade advancing into the wind.



At my location, the wind comes mainly from two directions (N-S) but the design are perfectly symmetrical for all four sides.

[dnix71]

In that drawing on the right the black area isn't actually blocking the wind. The trapped air creates a pressure vector 'up' in the drawing. As the top half of the blade moves down it must sweep out air under pressure. The curved funnels look like 1/2 would oppose the others when exhausting air.

You need to run a computer simulation on this. My guess is that you only need two deflectors on opposing corners to make this work.

[lifer]

Oh, I guess I've realized what you meant. Is this an improvment? (assuming wind comes from top and bottom mainly)



BTW, by "blocking unwanted wind" I meant diverting the flow to the useful side of the blade. Thank you for your nice explanations.

Do you know any software to run such simulations?

[electrondady1]

the savonius diagram makes sense but i question the usefulness of your shrouds in the case of a lenz 2 as it is a combination lift /drag devise . the down wind side is drag but the up wind side gets lift.
i caution you in regards to a large diameter vertical mill
i have seen one built in my area that ended up locked down permanently .
the mass in involved made it dangerous and subject to disintegration .
i went another route, and built several small diameter units side by side in a line facing the prevailing wind.

[lifer]

I hope it wouldn't affect the lift (too much). You can see in the diagram above that the wind still flow to both front side and back side of a blade.

Regarding the disintegration.. the rectangular outside frame will act as a "safety cage" and the VAWT top bearing will be mounted on a cross connected steel frame welded on top of that outside frame. I have enough experience with metal works (being a computer guy, anyway) so I'm not really affraid of this issue.

I still prefer these stationary guide vanes (to enlarge the swept area) instead o 2-3 smaller _moving_ mechanisms (wind turbines).

[electrondady1]

the original lenz was 3'wx4'h what sort of dia . are you proposing?

[lifer]

3.2m wide by 1.5-2m tall.. I know isn't the perfect ratio but it should work.

[electrondady1]

you might want to run this by ed , but if you go that wide, you may want to build the mill with 5 wings(or more) .
giving  less time between torque pulses.
the linear speed of the wings may be about the same but because of the increased dia. the rpm will be reduced. so the alternator will have a different cut in speed.

[lifer]

Good point! I wasn't aware of torque pulses & stuff..

But.. adding more wings wouldn't affect the working principle of Lenz2 wind turbine? If there's not eneough space between wings it might turn into a simple drag machine (Savonius), with lower efficiency. The rpm reduction it's not a problem as I would use a gearing system anyway. 

(Seems like I can't avoid building a small-scale prototype before going bigger).

[MattM]

I wouldn't alter the Lenz design ratios.  Vertical designs are notoriously inefficient and his designs remove guesswork and reinventing the wheel.

[lifer]

I've just talked with a town council guy and he told me that if I want to make it taller it should be some kind of "kinetic art", to accommodate with the architectural surroundings.

I've presented him some VAWT designs concepts and he pointed out to a helical/helix variant  But I still need it to be self starting and efficient so I came out to this idea(s):

1.

I've seen Lenz2 variants with two or more vertical stages, shifted by 60 degrees or so (the wings are interleaved). Now, what if I build small sections (half meter tall) of regular Lenz2 wings and mount them on top of each other but interleaved (120/n degrees)? It should look like a fragmented helix turbine. Does it still keep the lift/drag effect, like original Lenz2 design?

2.

Going even further.. what if I apply some torsion/radial deformation on a regular Lenz2 wing, so the top of the wing will be shifted with 60 degrees? Well, if I couldn't literally torsion an already built wing, I could design it from scratch to have such a torsioned shape - and finally look like a helix, again.

What do you guys think about it? (I'm affraid to ask Ed about it.. it' s a blasphemy, after all. BUT it might work??)

[dnix71]

If it has to be self starting then put a small Darrieus on top. Savonious and Darrieus are usually combined in real life anyway because both make up for the other's shortfalls. I'm not sure what qualifies as "art" where you live, but the two together would certainly be noticed.

[lifer]

But what about my suggested solutions?? I really like the Lenz2 design - it's so facile for diyers and have good efficiency.

Regarding the Darrieus design.. I'm more attracted by the Gorlov concept but I don't know how to calculate the blades (what airfoil type and what's the blade width versus turbine diameter/height).