Pitch and Angle of Attack

The aerodynamic center is defined in the profile properties. The orientation of the Aerodynamic Blade frame may be different from the Mechanical Blade Frame. Therefore the aerodynamic pitch is defined for each section in the Blade coordinate system. If the aerodynamic pitch is equal to the structural twist, the Mechanical Blade and Aerodynamic Blade frames are the same.

• The Aerodynamic reference frame orientation is defined at the beginning of the calculations based on the aerodynamic pitch provided as input.
• An initial pitch may be added (see control definition panel > pitch > initial pitch);
• During the simulation, the pitch instruction from the controller is applied to the root of the blade and the blade torsion stiffness propagates it along the blade.

The combination of the wind speed and the local blade speed due to the turbine rotation generates an incident flow with an attack angle alpha with respect to the blade reference frame. The aerodynamic forces are derived from the attack angle and the polar coefficients associated with a profile.