Author Topic: Volumetric wind turbine Challenge (Read 1268 times)

JohnMason · « **on:** July 29, 2020, 02:35:14 PM »

Hi Fieldliners!

I'm John I am writing in an attempt to foster support for a new type of versatile volumetric wind turbine which can capture energy in wind speeds as low as 2.5 mph.
I created a youtube playlist (find at "3D printable volumetric wind turbine model") of demonstration videos of a 3D printed model that demonstrates its possibilities. This 3D printable model is freely downloadable on thingiverse.com.

Two of the videos demonstrate how to test the model for its load carrying, Other videos demonstrate cut-in speeds and the fact that it can capture energy in any orientation to the wind.
There are several engineering hurdles to overcome but I am confident that this turbine can produce energy in low wind energy situations.

If any of you wind innovators would be interested in creating and testing a full scale (6' diameter?) working turbine with this type of blade I will lend what ever help that is needed. Even to the point of providing blades and rotor assembly.

Thanks John

MagnetJuice · « **Reply #1 on:** July 29, 2020, 04:08:30 PM »

Welcome to the Forum John,

That design looks promising. Just in case that a user here would be willing to work with you, please tell us where you are located in the U.S.

Have you done any calculating concerning RPM and TSR for a 6 Ft. diameter rotor?

I see that you recommend using ceramic or stainless steel bearings to minimize friction. Those bearings could be quite costly in larger sizes. If other type of regular inexpensive bearings were used, rotation would start at a slightly higher wind velocity. Could that affect the performance of the design?

Nice to have you here.

Ed

JohnMason · « **Reply #2 on:** July 29, 2020, 05:06:20 PM »

Hi Ed, Thanks for the welcome...glad to be here.

I live in Fort Worth Texas, but I can send the blade and rotor parts to wherever the collaborator(s) are. There will need to be some coordination of course.

The results of a 6' foot diameter prony brake field test.

These results reflect a bit of momentum in low wind conditions, in that higher energy from higher wind is carried into the numbers at low wind.
Alternatively, the higher wind conditions reflect inertia, in that there was not enough and long enough sustained wind to truly capture the high wind numbers therefore the numbers are understated.

Still I think this is a good starting point.

Thanks John

JohnMason · « **Reply #3 on:** July 29, 2020, 05:12:08 PM »

Hi Ed, Forgot about the bearing issue. The ceramic bearings are only for the very small 16" model. I used typical sealed steel BBs for the 6' foot model.

JW · « **Reply #4 on:** July 29, 2020, 07:20:57 PM »

https://www.researchgate.net/publication/316641745_Aerodynamic_performance_of_swept_blade_wind_turbine

JohnMason · « **Reply #5 on:** July 29, 2020, 07:31:43 PM »

Very interesting...looks theoretical. There is a patent in the USPTO for an elliptical blade of similar conformation. The difference is the research reflects a high aspect ratio blade. The volumetric is a very low aspect ratio blade so that it can capture more wind and power at low wind speeds

JW · « **Reply #6 on:** July 29, 2020, 07:37:48 PM »

Oh no I have been a "fieldliner" for years. Back in the day there was a user that had what was called a backwards windmill. DanB was around at the time and said Oh ya we've seen some of those but are rare. Before Dan said that we all thought they were crazy. There was actually a image posted of it spinning, and it was self furling.

JohnMason · « **Reply #7 on:** July 29, 2020, 09:46:27 PM »

Hi JW,

I am not exactly sure what you are referencing, backwards windmill? ...but all anyone has to do is to download the model make it and test for themselves.

I started with a Darrieus type windmill and cut the turbine in half so I could turn it sideways and make it work like a HAWT. It turns out that a hemispherical shape works the best. The problem of making the structure yaw was vexing but I think the model in the youtube videos works pretty well.

Thanks John

MagnetJuice · « **Reply #8 on:** July 29, 2020, 10:24:51 PM »

John, I love to work on projects like that. I spent a lot of time designing and testing systems and collecting data to solve manufacturing problems for a mid-size company years ago. It was challenging work, but at the same time, it was a lot of fun.

If I had the winds in my area, I would love to collaborate with you. The winds here are mostly in the winter and then only sporadic.

I was looking at that data that you uploaded and the RPM is different from a conventional high aspect ratio rotor.

It would be interesting to find out the torque that those blades can produce at high RPM, since they have most of the weight at the tips.

Texas is very good for wind power. It would be good if someone close to your area could collaborate with you. If not Texas, there are other areas in the U.S. with good steady winds. I hope that someone here can work with you.

Ed

JW · « **Reply #9 on:** July 30, 2020, 12:12:25 AM »

https://techxplore.com/news/2017-02-turbines-flexible-blades-efficient.html

still cant find the example im looking for if I find it I will make a new topic, carry on

JW

SparWeb · « **Reply #10 on:** July 30, 2020, 12:33:02 AM »

If there is some speed control due to flexing of the blades, and the orientation is for the blades to follow downwind of the tower, then a comparison can be made with a Proven Turbine.
The Proven (like so many, sadly) is no longer being sold but some still exist because they are quite durable. For a time the Provens were sold and serviced by Kingspan, but they are gone, too.
Here is what they looked like:
15KW: https://www.youtube.com/watch?v=92RIEfgErok
6kW: https://www.youtube.com/watch?v=5yVgOhqEKo0

I picked those videos because you can see some detail of the hinges built into the roots of the blades.

May I ask for a photograph of the machine you tested?
You referred to a prony-brake test, and I am very curious to see how that was done given the extremely compact hub in the CAD diagram.

JohnMason · « **Reply #11 on:** July 30, 2020, 01:57:28 AM »

Hi all

The whole idea behind this type of turbine is to be able to use it in low speed wind conditions so if you lived in a very windy area then this may not be the right choice.
But as the graphs above shows, a volumetric can in fact make better use of low speed surface level winds than a typical HAWT.

SparWeb
Speed control, yes that is a concern. The blades are very rigid. However, moving the blades edgeways does present less surface area and should be able to moderate the speed in that way. Turning the whole structure around will still allow it to function but at about half efficiency. Allowing the blades to flex backward would in effect create a wider diameter, which I guess would slow the blades but would also produce more torque. Is that a solution...I don't know.

I do have photographs of the 6' diameter rotor, thousands in fact that is how I recoded the measurements. It doesn't look anything like the model however. So I'm not sure if what you can tell.

The Prony brake in that instance consisted of two digital hook scales connected to a strap that ran across a pully I had a lever attached to a rope that was attached to one of the hook scales and adjusted the load by pulling down on the lever. The RPM was recorded by a cycling speedometer and the wind speed was recorded in frame on an anemometer with the hook scales and speedometer. The load was calculated by subtracting the low side scale from the high side scale. Yes it was complicated and I needed to take a ton of measurements for regression to the mean.

Thanks John

JohnMason · « **Reply #12 on:** July 30, 2020, 11:52:23 AM »

Testing the fiberglass blades 6' dia. rotor in the shop with a box fan.

Field Prony Brake Test Image. (yeah its ugly but it worked!)

SparWeb · « **Reply #13 on:** August 01, 2020, 02:46:19 PM »

OK then maybe I can't see how it works from the pictures and diagrams so far... got any that are more clear? Keen to see more.

Prony brake setup that I can see looks about right, and as you describe it.

Quote

it was complicated and I needed to take a ton of measurements for regression to the mean.

Yep. Par for the course.

JohnMason · « **Reply #14 on:** August 01, 2020, 04:15:42 PM »

SparWeb...

Yeah I should have better pictures of the whole setup. I tested this nine years ago, but as I said, thousands of pictures.

There is a difference in the conformation of the fiberglass prototype model that I tested in the field and the 3D printed model. If anyone wants the blades for a "X" diameter volumetric they will be 3D printed. Either you print or I print...will be glad to assist. The blades of the fiberglass model were 90º and conformed to a hemisphere. The 3D print blades are more like 70º. I cannot tell a difference in performance.

The fiberglass prototype was made from stuff I had in the shop and was dollied out into the field for testing. I made it so I could test it cup side down and cup side sideways if you catch my drift. There was yawing by way of man power. I suspect that a simple tail could be used for turning into the wind in any real application

Speed Control: I was just now thinking that instead of control by turning the turbine that a centrifugal brake could be employed.

I'll see if I can locate a few pictures.

John

JohnMason · « **Reply #15 on:** August 01, 2020, 08:16:33 PM »

Prototype

Prototype2

Prony Test Front-Flow

Prony Test Crossflow

Epic Fail

Formed Fiberglass Blade

SparWeb · « **Reply #16 on:** August 05, 2020, 03:40:16 AM »

Wow
What a project that was.
That's about 3x bigger than I thought at first.

Now that you're building again, have you made progress with those 2-foot blades you put in your video? Mounting on a hub?

OK it's time I asked the obvious question: Why are the blades angled forward in a curve?

JohnMason · « **Reply #17 on:** August 05, 2020, 04:20:12 AM »

Hi SW,

Why indeed!

The short answer is, that's what worked the best when I was testing in low wind speeds.

But the long answer...

Betz's limit, the total amount of energy that can be captured from a moving fluid, is based on a volume of fluid going through an imaginary plane. ...the practical limit is 45-50%

Which leaves half of the fluid free to go on to another turbine where it can capture 45-50% and so on until virtually all the energy is expended.

But what if it were not an imaginary plane...what if it where a real volume, what would happen then?

At this point you are talking less algebra and more integral calculus...I was never very good at calc. but I have a basic understanding.

From a practical point of view, more wind piles up in front of such a spatially dense structure as the volumetric, the more wind there is, the more it goes around the structure which makes it less efficient than a typical HAWT variety for high winds. ...but at low wind speeds...

The good news is that the gradual increase in energy output and the gradual decrease in efficiency as wind speed increases, should make it "generator friendly" with less need for braking. That's my theory anyway. I've never hooked it up to a real electrical generator.

That's where you guys and your particular expertise comes in.

Thanks John

Generator · « **Reply #18 on:** January 04, 2021, 07:41:49 PM »

Hi John, what size is this Wind turbine for which you have posted the results up to 125 watt?
I see you have bigger model too. Ever got chance to measure the power output of this? How much volts it generate? Can it light up 300Watt bulb or so?

News:

Author Topic: Volumetric wind turbine Challenge (Read 1268 times)