Const. windfield without shear,turbulence / AoA variations ?

Hi all,

We tried to calculate a rigid turbine with FAST in a constant windfield without wind shear and without turbulence.
To make sure that we did everything all right I simulated a TurbSim full field wind file and an output of .u .v .w .
The windfield has the same value of 11.4 at every grid point in the .u file and zero values at every grid point of the .v and .w file.
The rotational speed is constant for the whole simulation time, too.

When we had a look at the .elm AeroDyn output file we were wondering why the AoA varies with time, shouldn’t it be a constant value.
As far as I know the AoA is mainly dependend on the rotational speed, the radial position, the wind velocitiy and used airfoil( cl,cd value ) so my question is, what is the reason for the variation of the AoA. The Variation is about 1 degree so it is not neglible

The OoPDefl1 and IPDefl1 in the .out FAST output file have very small values of the order E-08 and the TwstDefl1 is zero. But I think that can not be the reason for the variations of the AoA.

Have you ever tried anything similar or do you know what I am missing.



Hi Andreas,

Is the shaft tilt of the wind turbine zero? How about the nacelle-yaw error? Nonzero values of these parameters will also cause oscillatory variations in the AoA in a rigid wind turbine.

Best regards,