angle of attack for a pitched VAWT

[Mecheng77777]

Hi,
Im currently trying to come up with a method for determining the angle of attack for a vertical axis wind turbine that is pitched (where omega R is not acting along the chord line) but so far to no avail, its been reckoning my head for a couple of weeks now,

I know for a fixed bladed its fairly straight forward to determine alpha, its just atan ((Vasin theta)/(va Cos theta +omegaR))

my problem is when Omega R is no longer acting on the chord line how does one go about determining alpha?

Thanks and help would be very much appreciated.

 

[rb1957]

does a VAWT blade resemble a swept wing ?

what do other VAWT designers do ?

another day in paradise, or is paradise one day closer ?

 

[btrueblood]

"angle of attack for a vertical axis wind turbine that is pitched"

Pitched being a condition analogous to "feathered" in standard rotary prop parlance?

" when Omega R is no longer acting on the chord line"

The only way I can think of that being relevant is when omega is zero, essentially the blades are rotated, or pitched, so that alpha for each blade is zero.

 

[rb1957]

i thought a VAWT had blades spiraled around the axis, hence like swept wings ...

another day in paradise, or is paradise one day closer ?

 

[Sparweb]

Don't you just need to add an incidence angle to the formula wrote?

I'm assuming what you mean is a VAWT with blades that pitch their angle of attack in or out. But RB1957 could be right, and you could also be referring to a helical-style VAWT blade. It's not perfectly clear which you mean.

Carefully choosing our terminology may be helpful here. Let me set up a co-oridnate system. The VAWT axis is the origin, looking down on the machine. If it rotates in the CCW direction, and the wind comes from the +Y direction, then the +X axis could be said to be where the blade is swinging up wind at zero angle of attack. If the blade, at the moment it passes the +X axis, has an incidence angle relative to the X axis, then you can use this co-ordinate system to account for the incidence in the equation for angle of attack you gave.

If this guess doesn't match the coordinate system you are actually using, then set out how you have arranged it, and that will make adding the incidence of the blade more clear.

You aren't building a Gyromill, are you?


STF