Advanced designs of vertical axis wind turbines?

[fastline12]

In looking at the aero data comparing horizontal and vertical axis, it is clear to see why horizontal is what is most typical for commercial installations. That being said, we are interested in building a couple experimental smaller vertical units and wondering if anyone has any data or relative experiences regarding optimistic data regarding vertical systems?

The units we would build would mostly be for advertising for us so certainly not doing this for a customer.

Seems the main issues we cannot get around right now is the lack of pitch tuning to optimize for wind speeds, and a potential drag component when a vane rotates to be parallel with the wind direction. I think our main attraction to these systems is much improved aesthetics as well as a potential to operate a low speeds thus minimizing noise.

 

[racookpe1978]

Several things I've read limit vertical axis machines:

Much lower net wind speed since wind speed GREATLY decreases near the ground, and is often "hid" behind buildings, trees, hills, and other towers even 10 to 20 diameters away. Almost by definition, a vertical axis machine is mounted on a building or frame for the generator at ground level, so the bottom half of the machine sees little wind forces. Or, looking the other way, you're building half the machine to generate reaction loads on the top half.

2. The vanes need to come back into the wind half the time. This can be minimized, but can't be eliminated. SO, only half of your half of your machine has to generate all of the power.

3. The machine doesn't need a directional device to turn it into the wind, but still needs a brake or speed limitor and controller to prevent over-speeding in storms. To BEGIN spinning in low speed winds, the vertical axis machine must be electrically turned at a pretty good rate to "catch" the wind and start generating power. A horizontal axis machine may not be making power byt 23 percent of the time - a average rate - but at least it is not consuming power with a motor at low speeds.

Good things? Low position of the generator. Slightly lower maintenance costs because of that. Less power cable requirements to go up the pole to the generator and control systems. Lower pole and foundation costs.

 

[fastline12]

I found a good article detailing most of the current and innovative designs for VAWT and seems many have stumbled inadvertently into a natural braking situation where the efficiency drops drastically at a high wind speeds and the drag increases thus creating a braking effect. No way to over speed. However, I cannot help but think that could be problematic in taking full advantage of wind, specifically gusts which around here can easily be 150% of sustained speed.

I would think an auto pitching system could be innovated "fairly" easily but fighting the effects of drag might be another issue. There was another venturi design that showed promise upwards of 80-90% eff which blows even HAWT away but seems to be tailored to smaller designs.

 

[rb1957]

vertical axis, why not ?

i'd've thought they were insensitive to wind direction (since they rotate through 360deg).

if the idea is just to get something spinning in the wind i'd've thought that was QED, there are several sitting on top of a nearby building, don't look too high tech.

i'm sure there's plenty of stuff out there on them.

 

[racookpe1978]

Well, yes, they are insensitive to wind direction - AT the CL of the turbine. But a building or hill or line of trees to the east or north will block winds from the east or north ... and thus, you lose power generating ability when the wind is form that direction.

Assume you have a "field" of 30 VAT's: they would have to be aligned n some grid or pattern -> they couldn't all be in a line. If so, when the wind swings, the VAT's "behind" the first row will receive less wind velocity, and so generate less power. They would cost the same, but are making no power. Assume you have a single line of VAT's on a north-south axis: Same problem: if the wind is not from the east or west, some of the turbines will get shielded from their upstream buddies. Now, if winds are from the east 80% of the time, then you'd be justified, and your turbine make make the world's average of a 23% availability factor x .80 . Otherwise? Even less.

However, only half of the VAT blades are going "downwind" getting force from the wind. The half of their sweep is going "upwind" creating resistance around the CL of the shaft. That is their biggest problem. Low efficiency of what little wind energy is actually present.

 

[KllrWolf]

The vertical turbines are great when in turbulent air, as the direction of the wind does not matter. This is great for places with buildings and such in the area and close to ground installations.

They do have a problem self starting at low wind speeds but with a little kick start it is possible. Once running, there is only a small, if any, drop in efficiency compared to a horizontal turbine due to the fact the blades are always at the optimal angle to the wind.

We have had several companies team up with the local university to look at wind generation, and they found that the vertical turbine actually stood up to the higher winds much better than the standard horizontal (one supposedly was fine at about 120 mph, until a tree hit it).

Another advantage is that they have a smaller footprint, thus being able to be used in more crowded location. We demo'ed one for a school project and achieved around 150 watts, and this was in an area with the building on two sides less than 20 ft away. We believe it could have easily achieved more, but that was the limit of the load/charge (that group did not believe a small home made unit would reach more than 50 watts).

 

[fastline12]

I am specifically targeting test data and designs that have achieved acceptable performance. I was specifically interested in the helical screw designs but the numbers are not looking all that optimistic. that being said, they might be inline with everything else.

 

[KllrWolf]

There are companies that sell the vertical turbines. The only helical screw designs I have seen have been advertised for placing on rooftops of houses. I would guess you could get basic performance data from them (and sort through the sales garbage).

 

[KENAT]

There is a lot of stuff out there fastline.

Are you talking Savonius or some variation on gyromill?

I'd read about the natural braking too on 'H' configurations. A professor at Reading University did a lot of work on 'H' configuration devices in the 90's as I recal, maybe you can find something. His earlier version had the brakes, but testing showed they weren't necessary due to the natural drag braking.

Biggest problem last time I looked at them was the 'pulse' of torque n (where n is number of blades) times per revolution. This very hi cyclic loading is a challenge for the torque tube from blade assy to the generator. Twisting the blades, I assume what you mean by helical above, addresses this but makes them more complex.

Maybe eliminate the torque tube, replace it with hydraulics or something, though that has it's own complexity & maintenance issues.

Self starting really isn't much of a problem, just incorporate a small Savonius with the gyromill and it will self start, though at the expense of drag.

I read an article just recently that VAWT's may actually make more efficient use of land available than the large HAWT's we usually see, so may end up being more efficient.

Also VAWT's can be mounted relatively high just like HAWT's, yes the bottom of the swept area is nearer the ground but that's true with HAWT's. Hell, maybe the design could be 'tapered' somehow over it's height so the bottom of the blades are optimized for slightly slower winds or something. Might be just washout down the length of the blade to increase effective AOA at the bottom or it could be another approach.

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[KENAT]

OH, and then there's the flapping version brought to us by our conservation of energy defying friends at 'fuel less flight' but I can't access their site from work.

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