I am trying to understand the aerodynamic center (AC) offset effects on aerodynamic moments as well as blade torsional deformations. I have read some topics on this forum, but some details still confused me a lot.
Firstly, according to my previous knowledges on airfoil aerodynamics, the AC was usually assumed at 0.25c of the chord line in wind tunnel experiments, but I find the AC positions vary from 0.25c to 0.125c from blade root to tip for the NREL 5MW wind turbine blade in the report  as follow:
Secondly, I find the AC offset can have a significant effect on the blade torsional deformations in BeamDyn as shown below where the BeamDyn (No AC offset) results are obtained by setting the “BlSwpAC” column in 5MW-AeroDyn_blade into zeros.
My understanding on the large differences is that the sectional normal force Fn and AC offset can introduce an additional nose-up aerodynamic moment, thus the aerodynamic moment on AC and 0.25c are different as:
Based on the previous facts, I have three major questions:
(1) Since the AC positions are not default at 0.25c in the original definition, can I understand that all simulations in terms of the NREL 5MW wind turbine, either using BEM method or actuator line method, must consider the AC offset effects for blade torsion predictions? Otherwise, the “wrong” wind turbine is simulated.
(2) Is my understanding on AC offset effects on aerodynamic moment generally reasonable?
(3) If (1) and (2) are yes, then I have the last major confusion that how the Cm-alpha curves in the provided airfoil tables are obtained? Specifically, which positions are the Cm values in airfoil tables are relative to? the AC positions defined in report ? or the traditional 0.25c? If they are relative to the defined AC positoins (like 0.125c) , then the Eq.(2) should be used to calculate aero-moments. However, if they are relative to the 0.25c, the direct usage of Eq.(1) seems enough? I really cannot figure out these confusions.
Please help me,
 J. Jonkman, S. Butterfield, W. Musial, G. Scott, Definition of a 5-MW Reference Wind Turbine for Offshore System Development, National Renewable Energy Laboratory, 2009.