Wind Speed Estimator (ROSCO)

1

Dear NREL,

We’ve coupled our structural solver to OpenFAST 3.5.3. We are getting good agreement for the main outputs like rotor speed, blade pitch, generator torque, generator power etc.

We are in the process of upgrading to OpenFAST 4.1.2, and are not yet getting close agreement. For a low wind speed e.g. 3m/s steady wind, blade pitch and rotor speed are in agreement. But we are seeing a divergence in generator torque which is leading to a difference in generator power. Based on investigations, we believe the discrepancies may be stemming from the wind speed estimates within the ServoDyn/ROSCO controller (ROSCO v 2.9.0).
Note: This is for IEA-15-240-RWT-UMaineSemi at 3 m/s steady wind speed. Base is fixed - no Hydro or MoorDyn effects

See below for comparisons of wind speed estimates (WE_Vw parameter) for both old and new versions.

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Could you advise on:

  1. What parameters are used to compute the wind speed estimates?

  2. What parameters should the structural solver pass to ServoDyn/AeroDyn in order for the wind speed estimates to be more consistent between the structural solver running OpenFAST, and OpenFAST running on its own?

Kind regards,

Ashok