Calculation of Aerodynamic Torque

[Stefan.Jespersen]

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: Select all

      ! integrate force/moments over blades by performing mesh transfer to hub point:
   force  = 0.0_ReKi
   moment = 0.0_ReKi
   do k=1,p%NumBlades
      call Transfer_Line2_to_Point( y%BladeLoad(k), m%HubLoad, m%B_L_2_H_P(k), ErrStat2, ErrMsg2, u%BladeMotion(k), u%HubMotion )
      force  = force  + m%HubLoad%force( :,1)
      moment = moment + m%HubLoad%moment(:,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)

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

Best regards Stefan

[Jason.Jonkman]

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: http://www.nrel.gov/docs/fy16osti/63203.pdf.

Best regards,