New propeller design

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New propeller design

Postby OooWeh on Sat Jan 19, 2013 1:56 pm

Hi Everyone.
I have casually browsed through these pages and am impressed with the knowledge they offer.
I live in Johannesburg where the wind leaves a lot to be desired.
As a handyman and kinetic art hobbyist, I stumbled across an idea for a new propeller design that takes full advantage of wind direction change and gusts at a low elevation of 2m.
My prototype is up and seems to run continuously during the day at 2m in suburbia reaching 4 revolutions per second from time to time. But averaging around 1 – 1.5
I invested in a bicycle speedometer and a weather station for a more accurate data and constructed a 9m high tower on which to mount this contraption - which I have not yet done, preferring to conduct low elevation tests first.
The first results are meaningless to me. Perhaps someone can help to decide whether this project is viable or not.
Prototype 1:
Measurements: Metric (mm)
Propeller Radius: 650
Propeller Diameter: 1300
Propeller Circumference: 4084
Propeller Surface Area: 424110
Attack angle: 22*
Sweep Area: 1327322
Propeller to Sweep area: 31%
Propeller Weight: 5.1 Kg

Measurements: Imperial (In)
Propeller Radius: 25.5
Propeller Diameter: 51
Propeller Circumference: 160
Propeller Surface Area: 657
Attack Angle: 22*
Sweep Area: 2043
Propeller to Sweep area: 32%
Propeller Weight: 112 lb

Average Weather:
Altitude: 1690m
Barometric Pressure: 82.54 kg/m3
Air Density: 0.98 kg/m3 at 20*c
Relative Humidity: 22% - 96%
Wind Speed: 1m/s - 7m/s
Temperature: 3*c – 25*c

Test 1:
A short lived wind of 7.2 km/h produced a speed of 40km/h at 2m elevation
Test 2: 6.1 - 42.6
Test 3: 3.6 - 33.6
Test 4: 5 - 30.8
Test 5: 3.6 - 26.4
Test 6:
Test 7:
Test 8:
Do these values hold much water and if so how much.
Please help if you can.
Posts: 3
Joined: Sat Jan 19, 2013 1:09 pm

Re: New propeller design

Postby windgat on Fri Jan 25, 2013 11:39 am

Compliments on a very thorough question! :thumbup:

Firstly, with a radius of .655m, the swept area is 1.33 sq metres.

According to our current understanding of Physics (c.f. Betz), the maximum power that it is possible to get from that area, at an arbitrary 10m/s (a strong wind!), is about (at sea level, so you would get a bit less up there)

0.35 * 1.33 * 1000 = 464.6W

This is at an impossible 100% efficiency. At 7.2km/h, = 2m/s, this maximum drops to 3.7W!

0.35 * 1.33 * 2 * 2 * 2 = 3.72W

Also, your propeller seems very large, and the attack angle is also large. This means it will rotate quite slowly (c.f. apparent wind). It would therefore need to generate a lot of torque to be effective. This is not an efficient combination to use for generating electricity.

Finally a comment about speed and power - they are not the same thing. So what matters is how hard the system can overcome resistance from the generator, not just how fast it can spin when there is no power being drawn from it.

Hope some of that help you!
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Location: Cape Town, South Africa

Re: New propeller design

Postby OooWeh on Sun Jul 28, 2013 9:11 am

Hi Windgat.
I apologize for not responding earlier as I assumed the forum was inactive.
Thanks for responding.
Our propeller is not a standard propeller. I took the liberty of calling it a "Ripeller" on the patent application. In fact there is nothing standard about our modular twin turbine at all.
The Ripellers were built for torque.

I get what Betz is about but that only affects those who try to prove him wrong. He made a calculation verified by a number of physicists and that's all good and well and has no bearing on me or my product at all.
Our turbine will produce 100% of its own capability at any given moment and yes, perhaps its only utilizing a percentage of the wind hitting the sweep area but as far as I'm concerned that's not important.
Much like a claim that one only receives 59% of gifts on Christmas morning. The gifts I receive will be 100% of the gifts I will get regardless of the gifts I may have gotten if some scientist hadn't made the claim in the first place.

Our alternator was designed resembling a cannery cage and the magnetic hub turns inside the stator. The stator turns in the opposite direction to the hub doubling the speed which is already geared to a ratio of 8/1 per Ripeller so in theory for every 1 revolution per second of both Ripellers the speed of the magnetic hub in relation to the stator is 16 revolutions per second or 960 Rpm
Bench tests on one Ripeller turning only the magnetic hub running at +- 600 Rpm gave me a result of 115 Volt Dc at 15 Amps generating 1.7 Kw.

The main design problems I have encountered are firstly I opted to use a solid steel pulley system of gearing which has made the machine heavy and cumbersome and secondly when the stator was mounted inside its steel casing the output voltage seemed to drop. Perhaps I should have made the casing in aluminum. I don't know.
The manufacturing engineer will deliver the final pulleys this coming week and then the contraption will be mounted on a 8m high tower for final tests.

I have worked on this prototype for 3 years full time alone and in isolation without any outside input or advise,
so I guess my main question is this - are there any wind turbine enthusiasts in the Johannesburg area that would like to share information and encouragement?

Posts: 3
Joined: Sat Jan 19, 2013 1:09 pm

Re: New propeller design

Postby windgat on Mon Mar 17, 2014 5:48 pm

Hi there. Did you find anyone to share your enthusiasm up there in Gauteng? I would be most interested to hear how your testing has been going!
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