Lenz Turbine update...

[windstuffnow]

  Well I think I exceeded even my expectations for the little machine.  Still in its rough form with a little cleaning up of the wings its doing .96 amps at 13.9 volts just over 13 watts.  This comes out to 43% of total or 73% of betz.  It's matched my 500 watt Horizontal machine efficiency.  

  I decided to check the losses occuring through the rectifier and alternator.  I found its loosing around a watt from the alternator and about the same through the rectifier.   I'm assuming 1.4 volts x amps = rectifier losses... is that correct?

  If it is then that means the turbine itself is making slightly over 15 watts in an 11.5 mph wind which exceeds my expectations ( and goals ) for the efficiency.  

  I played around with the air flow to see how the turbine reacted which was fun and interesting to see the outcome.  First I blocked the air to the downwind side.  It slowed the speed just below cut in on the alternator so I had no real way of accounting for the power.  But it carried a good portion of torque and a fair amount of pressure on the shaft to get it to slow down.  Blocking the upwind side yielded just under 1/2 the output ( .45 amps ).   I decided to see what it would do with a slight diffuser added.   Strangely enough it was very critical about the air flow.  Augmenting the downwind side lowered output and the same test on the up wind side yielded 1.2 amps @ 14 volts.  The diffuser angle seemed to be quite critical and it had to move the air onto the upwind blade at a very precice angle other wise it lost power. Moving diffuser very little in either direction made a large impact on the machine.

  For those who asked about the wing angle... it's set at 9 degrees ( tail toward the center of the machine ).  

  A question for Rotor... what did you use to make your tubercles?  I find a need to give it a try since I'm on a roll here... anything beyond what its doing now is simply a bonus!

  I've got it stuck in my mind that a little larger wing (diameter) may also increase lift a tiny bit more...

.

[kitno455]

ed, are you saying 73% of betz when you only count the upwind moving side, or are you counting both sides?

allan

[windstuffnow]

  Thats both sides, total area of the wind turbine.  

[ghurd]

Hi Ed!

Love your postings.

Even if most of it is past me.

Hate to bring bad news related to the total efficiency. But here it is.

I find the rectifier Vf to be lower than stated in the spec sheets, if the If is below the max rating.

The last check I remember showed a plain jane 3 cent 6A diode with about 1A at about 0.5Vf.  I recall other 6A surplus diodes running LED arrays at about 0.060A with 0.33Vf.  Those figure seem about average for what we do here.  Extrapolation says it is a non linear ratio of rated current to actual current, so it probably depends on your diode bridge more than anything.

Also, the higher the rated Vr, the lower the Vf, has showed up a few times.  I do not really do much testing related to that so it could just be an anomaly with the parts tested in that respect.  Ia max seems more relavent than Vr max.

The good news is you could try 35A 1000V bridges for 1A output!

The 1A output would surely increase the charging output by decreasing the bridge Vf.

Even better for output, but maybe not the eff% math, try the highest amperage and voltage Schottky diodes you can find for a bridge.

I now only work with DC. Not sure how AC, HZ, or pulsating DC will effect any of this.

Just my experiences.

G-

[rotornuts]

Even without the corrections 43% is fantastic for a vertical.

Ed, I made the tubercles out of flotation noodles that where 2.5" in diameter and they where spaced at 5". To make the tubercles I ccut a 1.5" wide sliver off the noodle to create .5" tall by 1.5" wide convex strips. After I cut them to length I shaped the lead edge and hot glued them in place.

http://www.pooltoy.com/noodchairand.html

For your unit I'd try a larger diameter and keep about the same spacing so in relation to thier size they'll be closer. I'd also bring them around the front of the lead edge to the cordline.

You may find something better to use but the surface roughness of the noodle is actually an advantage. The trick is to blend them into the surface of the wing.

These are of course only suggestions based on the couple experiments I did so call it a starting point and modify from there.

I really hope it helps your machine as I'm kinda excited about them but they may wind up being one of those things that only work over a narrow band like startup then hurt the rest of the range.

Mike

[bob g]

hi Ed:

not sure what your diffuser angle is, but somewhere in my engineering books on engines there is a section of intake manifold design as it relates to ram effect.

i believe that the maximum angle is about 13 degree's before the effect falls off, and and the air just piles up and spills over the diffuser.

i will look it up and see what the max angle is, i suspect there is a direct correlation between windrotor diffusers and that of ram tubes, as the effect and the medium(air) is the same.

also if i recall the angle is somewhat critical, inasmuch as the gains are pretty dramatic but in a narrow angular range.

there is also info on surface finish of the ram tube, in that a smooth surface does not move or allow air movement as well as a slightly rough surface. kind of like what happens with a golf ball with and without the dimples.

if you would like/ or are interested,  i will look into it, and get back with a post

bob g

[windstuffnow]

  Hi Bob,

    Thanks for the info... sounds interesting.  I'd bet I didn't make 13 deg before it dropped in power but I was in fact using a smooth shinny piece of aluminum.  Your mention of golf balls gave me an idea for another test ... gotta find my ball peen hammer !  I'm still looking for materials to make up some tubercles to try out tomorrow.  Also, I want to make a mount to fit on the front loader on my tractor and raise it into the air, its suppose to be fairly breezy tomorrow.  I need to know if my confined test results will change in free air.  My makeshift wind tunnel is far from perfect and still has a considerable amount of turbulance.

.

[kitno455]

ed, can we see pics of your wind tunnel? i am thinking that 73% of betz measured across the full frontal area seems really high, and i am wondering if your tunnel is such that the cone of air is confined in a way that prevents it from expanding leading up to the test subject? that kind of turbulence could actually help, because more of the unit is moving 'upwind'

although, i suppose that the upwind side could be over slowing the air, and the downwind side could be speeding it up again, so the overall could still be > 50% betz.

if we could only get rid of the downwind blades

allan

[windstuffnow]

  Thats the main reason I want to get it out into the open air for further testing.  I realize the turbulance and other wake created by the tunnel could enhance the readings somewhat.  I plan to bring it out into the wind later this afternoon... if all the mounting goes together quickly.

.

[Norm]

   Okay Ed !

            Good Luck !

                ( :>) Norm.

[DanG]

For test tubercles (theres a set of words for you) how about drywall compound? Good adhesion, rapid dry time, easily removed - I bet one could rig a tubercle form and make a mold that could stamp tubercles near identically from dabs of compound arranged on vanes, esp. once the drywall compound has started to set...

Glass bead 'sandblasting' can set up a good micro-texture on smooth mill finishes  - would be interesting to see what 2%, 20%, 40% (etc) coverage would do. With aluminum, using nozzle held back off aways (depends on air pressure) only the most robust beads leave a 'crater' while the rest polish the previous strikes...

[rotornuts]

I used Proset 30 setting drywall compound for filler on my helical Vawt. It has a 30 min set time but a substatally longer full dry time depending on conditions.

I think your idea would work well.

Mike

[MountainMan]

Can somebody provide some of the dimensional "rules of thumb" for VAWT's of this type.  

Reading the many posts here about HAWT's, I've come to understand some of the HAWT rules of thumb such as bigger means slower.

With a VAWT like this one or a savonius, isn't the rotational speed typically even slower than that of a "large" HAWT?  Does it get slower or faster with larger diameter?  What about speed vs. "length"?  By that I mean the dimension parallel to the axle.  

Other than the difficulty of building a mechanically stable unit, what changes as you make one of these bigger in both dimensions?  For instance, does size change the start-up wind speed?

Should a larger diameter beast have more "wings"?  

Does the number of wings change the startup wind speed and or the rotational speed of the VAWT for a given wind speed?

Sorry for the many questions.  Just trying to compare the rules of thumb for HAWT's and VAWT's

thanks,

jp

[windstuffnow]

  Hi jp,

    >>>With a VAWT like this one or a savonius, isn't the rotational speed typically even slower than that of a "large" HAWT?  Does it get slower or faster with larger diameter?  What about speed vs. "length"?  By that I mean the dimension parallel to the axle. <<<<

  Yes, the rpms are typically slower than the HAWT's.   Most drag based machines will run slower than the wind speed.  A savonius will produce the highest power at a TSR of around .33 or 1/3 the wind speed.  The larger the diameter the slower it will turn, height doesn't matter.  If its 2ft tall or 100 ft tall it will run the same speed in a given wind.

  The VAWT's typically have alot of torque where HAWT's have lower torque, depending on the version of HAWT.  Like the old water pumpers ( aermotor ) ran at or around a TSR of 1 and seldom exceeded an rpm of 105 in a 35mph wind.  Vawt's are very similar.

  A quickie formula for predicting the rpm of a turbine if the TSR is know is...

windspeed x 88 / (dia x Pi) x TSR

windspeed is in mph

dia is in feet

  The Lenz turbine runs a little faster while producing power.  It seems to like the .7 to .8 range.  The Savonius likes the .33 range and the HAWT's run anywhere from 1 up to 10.  Best power seems to be in the 4 - 8 range for most of them though.  

.

[MountainMan]

Thanks Ed,

I think that also means that the alternator design for any VAWT needs to have a lot more wire and magnets than one for a HAWT.  It seems you would need a three phase design, a larger diameter alternator to make room for a larger number of magnets and more coils, each coil should have many turns, and should probably be of the layered variety rather than the side by side coils.  In short, anything to have more magnets running past more turns of wire.

If VAWT's have more torque than HAWT's, and the speed stays the same regardless of length, I guess really long (or should that be "tall"?) VAWT's are not needed unless you can make an alternator that can make enough power at that low speed.  You might easily have to resort to gearing in order to make use of the power from a particularly tall VAWT.

I'm just thinking that a tall VAWT is probably not much more difficult to build than a short one.  Just longer pieces of PVC or whatever.  The drawback would be the difficulty of making an alternator that could make use of that extra torque at such a low speed.

If a 2kw HAWT is around 16 feet in diameter, that's about 3.14X8squared = 200 square feet of swept area.  Does that mean that a VAWT with the same area, maybe 4 feet diameter (used in the equation as a "width" of the area blocking wind) would need to be about 50 feet "high"? to cover the same area and make the same amount of power?  To put that another way, 4 feet diameter and 10 feet long (full length of PVC pipe) would only be around 400 watts?  Am I in the ball park?  Seems like a pretty big unit for just 400 watts.

Here's a thought...Make about 10 of them, each maybe 4 feet tall or less to make it simple. Take each one to it's own bridge rectifier, and then put those DC outputs in series to get a higher voltage.  This way your alternators can be "normal" HAWT type alternators, with a low voltage output (because of the slow speed) from each one, but with a high total.  I know that you are all thinking "oh my god, 10 towers?"  Nope, I'm planning to go against all reason and plop them right on the ground...with a 10 mph wind racing up the hill right at them.

jp

[electrondady1]

mt.man, i have come to very similar conclusions in regards to both genni and mill design . i would like to build on a scale that would not require a top bearing or guy wires. a single robust bearing/generator assembly at chest height would be ideal for me. as far as the genni design goes , it would seem practical to make the dia of the mag. disks about the same as the dia. of the vanes . for me thats about 22".it would be possible to place a lot of long skinny mags. on a 22"dia disk.