Blades noise

[xxzxxz]

Hello.

We try build turbine for 2 kWt.
Our blades diametr 2,4 m.

Our problem - noize.
We think about more ergonomic form, but maybe noise shield more effective?

But there are we get second problem - small average wind speed per year (~3 m.per sec).
We think about 9 blades via different inclination in degrees 15, 30, 45.
Blades material - alluminium (for tests only - low prise)

May be anybody can give me an advice?

ps sorry for bad english )))

[hiker]

try a length of weedeater string on each blade..just past the high point on the airfoil side of the blade
on the downward slope....might check the old postings--this has came up before....

[kitestrings]

xxz,

If you can provide more details you might get better feedback.  I assume it is an axial design?  Noise can come form a few things: running them too fast, or unloaded, too thick a trailing edge, rough surface or loose edges/blade tape, etc. (usually when they are well-worn).

From what I've read you don't necessarily gain more with more blades.  Marlec has used 6-blade units for some designs; mostly quite small.  Interestingly, their blades are very thin, and very quiet.

I don't think there's a fix for low wind site, other than getting it up higher.  If the average is constant, low winds it may not work well.  If there are some good wind months, and some with little or no wind, you might find this compliments a PV system nicely as many here  report.  We have a pretty good site, but our poorest months are usually when the sun is a bigger contributor, days are longer...

Good luck, ~ks

[Flux]

You need to give a lot more detail to get any help. Kitestrings has covered the basics, given what we know.

When you are asking about 9 blades at 15 to 45deg I can't help feeling you are using paddles not blades.

There may be some merit in using more than 3 blades in a very low wind area if you are not using an air gap alternator, but in such low winds I suspect you will need an axial air gap alternator to do any good, with an iron cored machine you may not supply the iron loss.

If the wind is a constant 3m/s every day you will get very little. If it is still on some days and reasonablly windy on others you may manage something. 3 m/s is right at the lower limit of viability for wind power.

To see your 2kW from a 2.4m rotor you will need about 14m/s and in a wind area with average 3m/s you may never see it.

Tell us more about your alternator and blades.

Flux

[xxzxxz]

Thx 2 all for fast answer.
I was in business trip - sorry.
Its was nice place with out of internet, mobile phones and roads (((

2 hiker
Sorry, but English is not my native language. Could you give a synonym of the word "weedeater". ))))

2 kitestrings & Flux
Yes, I thint - it`s axial design ))) I think - it`s classik form of wind generator))) I can show you stator  https://doc-0c-30-docs.googleusercontent.com/docs/securesc/ha0ro937gcuc7l7deffksulhg5h7mbp1/ng5a2gtc3tst578j4keodnb0efen15ld/1394733600000/13180374276935555689/*/0BxA7ngb-rj--UlI4UzcxQ3RMTG8?h=16653014193614665626&e=download

My problem is not "too thick a trailing edge, rough surface or loose edges/blade tape", we take alluminium blades via laser cutting. I think more like paddle than classic blades. Make alluminium blades via lathe - very expensive.
Paddle of surface like ideal . It is smooth and varnished.
Now we build prototype only. Course at future I`ll take GRP or carbon for blades - it`s not hard tehnology. But now I want to understand the causal relationship.

I know, thats aviation and spase solve this problem by notches and holes. But how?
Maybe there is some book or guide on this problem?


In light winds we used laminar flow model of fluid flow in the pipe. For this reason, we recognized the need to sew to make 3 of the inclination of the blade. During strong winds, we will lose some energy resistance, but given the general inertia of this fact can be neglected. This fact was decisive in choosing the material for the prototype blades.
If we make a mistake, you can make vegda high tower ))))

[DamonHD]

In British English, "strimmer":

https://www.google.co.uk/search?q=strimmer&client=firefox-a&hs=2dY&rls=org.mozilla:en-US:official&channel=sb&source=lnms&tbm=isch&sa=X&ei=2hUiU4TqBM-AhAemloHICg&ved=0CAoQ_AUoAg&biw=1215&bih=775

Rgds

Damon

[xxzxxz]

Thank you DamonHD.
I forgot about the fact that soon the summer))))

It`s good idea. I`ll try.

2 all.
I do not remember very well the physics, but the noise should occur because the field thin air, pursuing blade.
Thanks