Dear Matthias,
The blade azimuth angle output from AeroDyn v15 is not the rigid-body rotation of the rotor, but defines the orientation of blade relative to skewed inflow–see the following forum topic for more information: Azimuth Angle of the Blade - #10 by Jason.Jonkman.
The Azimuth output from ElastoDyn is likely more in line with what you expect.
Best regards,