I’m running some simulations just using AeroDyn to get some information about local angle of attack at different TSRs. I want to make sure my blade data file has the correct information in the twist column and would greatly appreciate it if you could clarify the blade twist definition!
From OpenFAST readthedocs (Section 4.2.3.19.2. Blade Data Input File):
“BlTwist specifies the local aerodynamic twist angle (in degrees) of the airfoil; it is the orientation of the local chord about the vector normal to the plane of the airfoil, positive to feather, leading edge upwind; the blade-pitch angle will be added to the local twist;”
Is “vector normal to the plane of the airfoil” referring to the blade’s rotational axis/pitching axis (defined at z_b in AeroDyn driver section)? If so, is this angle referenced from the rotor plane to the local chord line? Additionally, is the blade twist angle defined about the blade root or tip? For example, in Hansen’s Aerodynamics of Wind Turbines and Manwell’s Wind Energy Explained, blade pitch angle and twist angle are defined with respect to the tip chord.
Additionally, at the end of Section 4.2.3.19.2, the documentation references a figure specifically for twist. I’m not sure if it’s a typo, but shouldn’t theta (local pitch) = pitch angle + twist in this figure?
Thank you so much for your help and response,
Megan Andersen