Need some help,

[Alain Langlois]

- I am working on a project to oxygenate a small man made lake using a wind generator coupled to a small compressor.

My first design did work well for about 10 months until a blade off (used my how concept based on the NACA4412 plus 30%).

So I did a minor modifications to my hub to finally install some production made Chines blades ( 10.5 dia.). I did started using 3 blades than moved to 6 (need high torque to start rotation). Now my problem is that I am not sure if the angle of attack is correct because I need approx 25 km of wing to start the process. I need to increase the pitch but these blade look so awkward that I am not sure wich way to go.

Attached you will find few pictures of the old versus new blades installation.

Please help me......

Sorry for my writting...

[Stewart Corman]

Alain,
as a basic answer for a place to start re fixed pitch setting angle, I would recommend reading the reports out of Clarkson:
http://72.14.205.104/search?q=cache:3UhNhaOaGGIJ:www.clarkson.edu/honors/research/papers/Rector-M.%2520Curtis.doc+%22Solidity+and+blade+number%22+ Clarkson&hl=en&ct=clnk&cd=2&gl=us&lr=lang_en
click on the document link to get all the charts and pics

IMHO, bottom line is to shoot for a TSR of about 4 with a pitch angle of 15 degrees on your 6 bladed hub.

OT ...I presume you are using a compressor with pistons mechanically attached to the rotor, rather than making electricity and running an electric compressor.
using a wind generator coupled to a small compressorAren't there other ways to aerate at a poind other than using such an arrangement? I would think a high volume blower or rotary vane air pump could create enough pressure head to run banks of aeration stones like in a fish tank.
The advantage is that there would be little/no drag when the unit first starts up. I have a small vane pump that could produce 30 psi but at low volume rate.
do an eBay search on "GAST air motor" ...I am not sure if these can run in reverse ??
But I did see that Gast makes air pumps that can be used for either vaccuum or pressure and some models are used in the septic systems for aerators:
http://www.septicsolutions.net/store/RV_Series_Specs.pdf

note that most of these are fractional hp ...your turbine can produce 2hp in 20mph wind

Stew Corman from sunny Endicott

[Alain Langlois]

Thanks for the precious inputs.
The compressor installed at the moment is a single stage unit, much less drag than a two stages model. My previous blades were adjusted to be in motion with only 8 to 10 km of wind, so very little wind was required to beat the friction of the compressor and the bearing / brake system. The air diffusor used in the lake are made of special membrane that prevent the water to flow back in the piping ( to prevent installation of a check valve). To initiate the process I need to build up approx 5 psig of pressure to over come the head pressure of the water. In high wind condition the compressor will start to produce more pressure and at 9 psig the brake system is trigger for approx 10 hours, used a check valve with a slow leak. The brake system is made of a disc brake of a motor cycle and the air actuator to drive the master cylinder is from a truck ( tractor forward braking system).
I glad the ear that the windturbine can produce up to 2 HP, so if the blade angle is correct maybe I could install a multiplication of 2 or 3 to one.
When I found that I was getting poor results with the new blades, I did some test with reduced friction like no compressor nor braking system and the end results was approx. the same.
With the actual blade design it is very hard to change the blade angle, need to fabricate wedges and redrill the holes. My little background is from aircraft propeller so I know very little on the wind generator blade profile. I my world the covex side of the blade is facing the wind but in the windmill industry it seem to be to opposite. Would you please tell me if my blades are installed correctly, wich side is the leading and trailing edge and finally How to set the angle of attack. I seem to come from very far but it was so easy with my old blade design.......

Thanks again.

[Rob Beckers]

Hi Alain,

Another good source for info on blade pitch, TSR, and more, are Hugh's lecture notes: http://users.aber.ac.uk/iri/WIND/TECH/WPcourse/index.html

-Rob-

[Stewart Corman]

Alain,
You have better defined your setup, but it leads to more questions.

First I'll make a few comments and answer your blade pitch setting question.
I agree with Rob that Hugh Piggott's link is a good one with many equations and all the info derived by Clarkson's research can be traced back to Hugh's tutorial ..no contradictions ...it is just that Hugh fixates on 3 blades and TSR=7 as optimum ..it isn't ! but it is easier to manufacture and get better "spec numbers" at 28mph WS, which is irrelevant for all of us with low avg WS

For wind turbines, the flat side faces the wind and for a non twist blade, the convex side away, and the setting angle is simply the angle measured from the cord (line drawn across the widest portion of the blade profile) at the tip end of the blade to the rotor plane. If there is twist designed into the blade profile, the common definition is at the 75% station or 3/4 of the way from rotor axle to tip. Typically of the Naca4412 you had before, there is about 4 degrees from the flat surface to the cord line, the fiberglass blade is a bit different, so just measure it.
The more pitch you have, the greater the torque and the slower the maximum rpm. Maxiumum efficiency of 40%+ is somewhere around TSR=3.5

I'm glad to hear that the windturbine can produce up to 2 HP, so if the blade angle is correct maybe I could install a multiplication of 2 or 3 to one.hmmm, this means you could use extra aeration if you had it ???...so why do you use a brake ??? you are wasting wind power into mechanical heating of the brake mechanism ...why not use a simple pressure regulator to limit the max pressure applied to your exisitng unit and use some sort of solenoid valve to open other ports to other aerators when the wind is blowing harder.

BTW, I would keep the brake assembly as a means to lock up the turbine in high winds

BTW, an alternative to a real compressor may be to simply run a water pump and use a Bernouli air injector, which atomizes the air as it run through a tube:
http://en.wikipedia.org/wiki/Injector
The faster the pump turns the more air is injected ...no other moving parts except the impeller! This would provide circulation in the pond as well as aeration. Nothing to clog or plug

I have a much simplier unit installed on my aerobic domestic water iron/sulphur filtration device than that shown in the diagram.

With the actual blade design it is very hard to change the blade angle, need to fabricate wedges and redrill the holes. Did you consider using Ubolts and clamping the flat mounting section to a short piece of pipe so you could rotate the setting angle at will??

http://i145.photobucket.com/albums/r203/scorman1/Turbine%20project/4367.jpg
mine has the tubular spar fixed to the blade and the spars bolted to the rotor for pitch setting, yours is the opposite ..the rotor could have 6 spars welded to a plate and each blade fixed to a spar with similar Ubolts or exhaust clamps

Check out this link:
http://www.windmillwaterpumps.com/articles/2006/02/aerating-ponds-and-dugouts.html

Stew Corman from sunny Endicott