# Calculation of Aerodynamic Torque

Dear forum

As a part of my master thesis I am currently working on a turbine model which is ultimately going to be used for control design purposes.
I wrote a BEMT code in MATLAB, but after comparison with FAST I noticed that the thrust force was almost the same, while the aerodynamic torque was quite off.
In the FAST simulation I have set all DOF’s to zero except for the rotation, and applied a uniform and constant wind field.
In my code I assume a linear variation in the tangential loads between each node point on the blade, when I carry out integration.
My question is:
How is the aerodynamic torque found in Aerodyn? Is it also assuming linear variation of the tangential loads, or is it held constant for each element under integration?
I wasn’t able to decipher this in the source code and didn’t find the answer to this in the documentation either.

I noticed this section in the AeroDyn_IO.f90 file:

[code] ! integrate force/moments over blades by performing mesh transfer to hub point:
force = 0.0_ReKi
moment = 0.0_ReKi
force = force + m%HubLoad%force( :,1)
end do
tmp = matmul( u%HubMotion%Orientation(:,:,1), force )
m%AllOuts( RtAeroFxh ) = tmp(1)
m%AllOuts( RtAeroFyh ) = tmp(2)
m%AllOuts( RtAeroFzh ) = tmp(3)

tmp = matmul( u%HubMotion%Orientation(:,:,1), moment )
m%AllOuts( RtAeroMxh ) = tmp(1)
m%AllOuts( RtAeroMyh ) = tmp(2)
m%AllOuts( RtAeroMzh ) = tmp(3)[/code]

Does the function “Transfer_Line2_to_Point” find the force and moment on each blade? or how does it work?

Best regards Stefan

Dear Stefan,

Effectively, AeroDyn integrates the distributed loads (per unit length) that are calculated at the aerodynamic analysis nodes along the blade based on a linear variation of load between the nodes. The Transfer_Line2_to_Point routine is the mesh-mapping routine that integrates distributed loads (per unit length) and lumps them at point (in this case the hub), including moment arms for the moments. The mesh-mapping routines implemented in FAST are described in detail in the following report: nrel.gov/docs/fy16osti/63203.pdf.

Best regards,