Extracting power from wind...

[Externet]

A 3 blade turbine, and a 12 blade turbine; being both the same diameter

 

http://econewmexico.com/system/files/images/wind-turbine-wind-mill.jpg

 

Which one is more efficient, can produce more power ?

 

There has to be other variables as blade pitch, blades area, speed... even temperature... What formula applies to find out the power that can be extracted from a given wind speed ?

 

Asking this because a large count blades turbine presents a larger blockage and reaction to wind than a 3 bladed one as the modern turbines are designed. There has too be other economical and construction factors involved to choose one or the other, but as amount of wind capture, one has clear advantage.

[J.C.MacSwell]

A 3 blade turbine, and a 12 blade turbine; being both the same diameter

 

http://econewmexico.com/system/files/images/wind-turbine-wind-mill.jpg

 

Which one is more efficient, can produce more power ?

 

There has to be other variables as blade pitch, blades area, speed... even temperature... What formula applies to find out the power that can be extracted from a given wind speed ?

 

Asking this because a large count blades turbine presents a larger blockage and reaction to wind than a 3 bladed one as the modern turbines are designed. There has too be other economical and construction factors involved to choose one or the other, but as amount of wind capture, one has clear advantage.

 

Generally the 3 blade has the advantage, other than start-up. If you slow the wind too much in an attempt to get more power, you actually end up with less, as the upstream wind is diverted around the swept area of the blades and that energy with it.

[Mr Skeptic]

The many blade turbine would produce more power. However, if you make fewer, longer blades, that seems the better option for getting wind power.

[gcol]

For the amount of energy extractable from the wind, investigate the "Betz Limit". (My imperfect memory is telling me that only up to about 50% of the wind power is extractable).

 

A multi-blade prop will generate its power (torque) at lower rpm, and at the other extreme, a single blader (dynamically balanced, of course) will generate its power at much higher revs. The 3-blader is favoured by the windpowe boys as a practical compromise, but for water pumping at low revs a multi-blader is preferred.

 

The multi-blader presents a virtual solid disk to the wind at lower revs

 

Chose the revs you want, then build a blade system to suit.

 

By the way, a two-blader has unwanted gyroscopic effects as it swings about to face the wind.

[hobz]

A multi-blade prop will generate its power (torque) at lower rpm, and at the other extreme, a single blader (dynamically balanced, of course) will generate its power at much higher revs.

 

How come?

[J.C.MacSwell]

How come?

 

Multi blade props have more "sail area". That sail area can develop more torque than less sail area. When the prop speeds up the blades are interfering with each other, there is not enough energy to go around. 2 and 3 blade props are all that is required to get the maximum energy from the swept area of the prop.

[hobz]

Thanks! I understand now.