Blades

[Ingesson]

Hello.

I have built a Wind turbine from Hugh Piggots recepie book.It`s 4,2 meters.I did not make the blades
from the book however.Instead I made  with NACCA 4412-4416 profile.The tip of the blades are quite
pointed.They run well but there is a noise I don`t like.Sounds like birds singing at higher rpm.
Does anyone have any knwoledge or experience of Hugh Piggotts blade design.How efficient is it
and how much noice does it make?It seems quite simple in design and easy to make.

Best regards
Jan

[SparWeb]

I was able to reduce the tip noise by rounding the tips of my blades.
My blades are not exactly Piggott blades, but they are very similar, and also use NACA profile.
I can hear a "swish" now, but you should not hear a "bird whistle" sound.
Do you know if the blades happen to be turning too quickly?
High tip speed also causes noise to increase. 
Have the blades always been noisy or has their noise changed lately?
Does one blade seem to make more noise than the others?

[clockmanFRA]

I have 3off, Hugh Piggott design Wind Turbines at 3.7m dia.

One is Cedar blades, the other two turbines are fiberglass to Hugh Piggotts design.

No Noise from any of them, when close up just a slight whoosing sound.

When under load, charging the batteries, then there is a faint HUM.

The blades don't need to turn fast, they are low RPM, are you loading the turbine?

[Ingesson]

Hello.

I have built a Wind turbine from Hugh Piggots recepie book.It`s 4,2 meters.I did not make the blades
from the book however.Instead I made  with NACCA 4412-4416 profile.The tip of the blades are quite
pointed.They run well but there is a noise I don`t like.Sounds like birds singing at higher rpm.
Does anyone have any knwoledge or experience of Hugh Piggotts blade design.How efficient is it
and how much noice does it make?It seems quite simple in design and easy to make.

Best regards
Jan

I have 3off, Hugh Piggott design Wind Turbines at 3.7m dia.

One is Cedar blades, the other two turbines are fiberglass to Hugh Piggotts design.

No Noise from any of them, when close up just a slight whoosing sound.

When under load, charging the batteries, then there is a faint HUM.

The blades don't need to turn fast, they are low RPM, are you loading the turbine?

I was able to reduce the tip noise by rounding the tips of my blades.
My blades are not exactly Piggott blades, but they are very similar, and also use NACA profile.
I can hear a "swish" now, but you should not hear a "bird whistle" sound.
Do you know if the blades happen to be turning too quickly?
High tip speed also causes noise to increase. 
Have the blades always been noisy or has their noise changed lately?
Does one blade seem to make more noise than the others?

Thanks for your respond.The "bird whistling" noise appear from around 140 RPM.At lower RPM there is almost no noise at all.
I`m sure if the blades are running too quickly.I could try to lower the RPM by adding more load.
Maybe the noise is more noticeable now than when the blades were new.Hard to say.Do you think that the angle of the blades could
have changed over time.I have planned to take the turbine down to check it anyway soon so I could check angle of the blades and
if there is difference between them.

[SparWeb]

There is something wrong if 140 RPM causes your blade tips to whistle.  The tip velocity is only 30 meters per second with your blade diameter.
Also, 140 RPM is not very fast - how much faster do you see them turn, and in what wind speed (do you know?)  Have you seen it furl yet?

Checking the angle of the blade tips is a good start.  While you have it down, make sure to look for other sources of noise (it is possible).

Can you describe the load on the turbine?  Did you build the alternator according to Hugh Piggott's plans?  Do you use it for battery charge and is that functioning correctly? 

[stofanel]

Blade noise indicates either flutter (mechanical vibration) or blade tip vortex noise (aerodynamic vortex shedding). Unless the blades are really flimsy, it's quite unlikely that we are talking about mechanical vibration, which leads me to believe that you have an aerodynamic problem. Most likely the blades you are using have incorrect twist or chord in the tip section. At high RPMs, the effective angle of attack of the blade airfoil decreases, which may force some blade tips to produce negative lift. This opens a whole new can of aerodynamic worms.

The only solutions to this problems are to either limit the turbine RPMs (which hurts efficiency), or cut off the tips of the blades. This may seem counterintuitive at first because of the reduced swept area, but given the likely scenario of incorrect blade twist, it may be the only sensible solution. 

[kitewinder]

Hello All,
I'm the founder of a french start up located in bordeaux and named Kitewinder.
Olivier Normand

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