Incorrect Unstead Airfoil Aerodynamic Input Parameters

[jjonkman]

I would normally expect the unsteady airfoil aerodynamics (UA) model of OpenFAST / AeroDyn to influence the variations of lift about the mean, but not to directly influence the mean lift itself. However, Mehran Saeedi on our forum noticed that the mean lift is being impacted for some airfoils, e.g., the DU25 airfoil in the NREL 5-MW baseline models--see the figure below.

This is likely the result of inconsistencies between the UA parameters and the the static airfoil data in the AeroDyn v15 airfoil data file. These inconsistencies should be fixed in the sample OpenFAST models provided in the r-test. I'm not sure where the UA parameters originated from for all airfoils, but I would guess a mistake was made when the AeroDyn v15 airfoil data input files were first made, at least for some airfoils.

I know that there are scripts floating around that can be used to derive the UA parameters from the static airfoil data. It would be great if these scripts could be used to update the AeroDyn v15 airfoil data files.

For more information, see the related discussion on the forum: https://wind.nrel.gov/forum/wind/viewtopic.php?f=2&t=2492.

[jjonkman]

The reason for the offset in lift between the static lift and lift with UAMod = 3 solution has been found, as recently commented in the forum topic linked above. The problem is related to nonlinearity in what should have been a the linear region of the lift curve. Two solutions are outlined in the forum.