Wind/Rotor misalignment and estimated wind speed

[dzalkind]

Discussed in #317

^{Originally posted by ghuwart February 15, 2024}
Dear all,

I am running some misaligned simulations with ROSCO and TSR tracking (VS_ControlMode=2).
I am using the filtered hub wind speed as the wind speed estimtor (WE_Mode=0) even though I've seen it is recommended to use at least the mode 1 as advised in #147 but my point is something else.

From my understanding, the estimated rotor speed should be the wind speed facing the rotor as it will be component that contributes the most to the motion of the turbine. Nevertheless, the wind speed read in avrSWAP(27) is the horizontal wind speed, i.e., the norm of the wind speed in the horizontal plane. That is what I saw in the OPENFAST code and this is what is read directly in mode 0 of the Wind speed estimator (see here in ControllerBlocks.f90).

When running with a misalignment, this can introduce undesired effects. In some of my cases, such as gust with extreme change of direction, the difference between the wind speed facing the rotor (around 6 m/s) and the norm (around 22 m/s) is hugely impactful since the control points are not the ones desired.

I reckon this is a fringe case but I think even standard production cases with misalignment could be affected with a 1 or 2% error on the "correct" wind speed for the TSR tracking.

Is my understanding of the situation correct?

Could we use avrSWAP(24), i.e., the measured yaw error to get the component of avrSWAP(27) facing the rotor?

Thank you.