FAST output force decreases when wind speed increases

This is my first question, hope it is a meaningful one.

I generate Wind input files using Turbsim, of NTM Wind type , and I only change the ‘URef’ (mean Wind speed at reference height) from 0m/s-25m/s, and then the Wind file are used by FAST.

the figure enclosed is the output of FAST at different Wind speeds .

'for example : 'TwrBsFxt ’ (tower base for-aft shear force)

my question is : why the shear force of Wind speed 20m/s (green line) is smaller than the shear force of Wind speed 15m/s (purple line),

except at the begining of simulation, when the turbine is unstable. the magnitude is proportional to Wind speed.


Hongbo Zh

Dear Hongbo,

You haven’t described what turbine you are simulating or your simulation settings. However, For a standard variable-speed, pitch-to-feather controlled wind turbine, I would expect the mean thrust load to increase with mean wind speed up to rated wind speed (often between 10-12 m/s, depending on the turbine) and then drop again with increasing wind speed due to the pitch-to-feather operation. Is that what you are seeing?

Best regards,