Definition of rotor Azimuth and Azimuth Outputs

Dear all,

I am a little confused about the definition and outputs of the rotor and Blades’ azimuth angles. I am studying the effect of Blade passing on the tower wind loads, and need therefore accurate information of the rotor and blade positions.
After reading the Manuals, I have used the Inputs Azimuth=0 and AzimB1Up=0 in ElastoDyn, which I thought would lead to the simulations always starting with Blade1 looking up (and that would be Azimuth=0). To check, I used the outputs Azimuth, BXAzimuth and TipclrncX (X=1,2,3). Looking at the results, the Azimuth and Tipclrnc outputs seem to confirm my hypothesis, but the outputs BXAzimuth start with an azimuth offset of around 100°. Am I not understanding something?
I am using the NREL5MW turbine, I attach a figure with the results and the ElastoDyn, Aerodyn and Primary Fast inputs.

Thanks a lot in advance for your help,
Robert Fontecha

Dear Robert,

The local blade azimuth angle output from AeroDyn v15 does not use AzimB1Up, which is only defined/used in ElastoDyn. Instead, in AeroDyn v15, the local blade azimuth angle is defined based on how the rotor disk-averaged relative projects onto the disk (based on the skew angle between the rotor axis and inflow). Please see the following forum topic for more discussion on this: http://forums.nrel.gov/t/azimuth-angle-of-the-blade/1464/10.

Best regards,

Dear Jason,
thanks a lot for your quick response! I will then use the ElastoDyn Azimuth angle to locate the blade passing.
Best regards,
Robert Fontecha