What setting should I choose for “'ignore blade shear center axis orientation transformation”?
This option allows users to control whether the orientation difference between the shear axis and neutral axis is taken into account in the blade cross sectional stiffness matrix. Full theoretical details can be found in the document Bend Twist Coupling in Bladed Beam Elements
The shear axis orientation transformation was originally implemented in Bladed to deal with a situation where blade designers added local cross section reinforcement typically near the blade root. Such reinforcement moves the elastic (bending) centre, but does not much affect the shear centre, and as such blade torsion should not change much when such local reinforcement is added. In order to reduce the sensitivity of torsion deflection to local blade design changes, a transformation was introduced that accounted for the orientation difference between the shear and neutral axes. This means that the beam torsion axis is around the shear axis orientation rather than around the neutral axis orientation.
However, in some blades, the shear centre axis can be non-smooth in the spanwise direction, as the centre is quite different between subsequent stations. This can result in the torsion axis (shear axis) being quite misaligned from the expected direction (i.e. roughly following the pre-bend blade local Z direction). As the torsion stiffness is low, the torsion axis direction can have a significant effect on the blade deflection. With the transformation enabled, for some blades, the torsional deflection on the blade can become non smooth and potentially non-physical. Therefore some blade designers prefer to assume that the torsion axis is parallel to the neutral axis, which is possible by selecting “'ignore blade shear center axis orientation transformation”.
It is the blade designer’s responsibility to make the choice on this setting depending on the blade properties, design and modelling approach used for the blade.
Note that this comparison to HAWC2 had the setting “'ignore blade shear center axis orientation transformation” activated in order to match the assumptions in HAWC2.