15 MW Turbine Loading

Wind & Water Rotor Aerodynamics
1

Dear all:

I have 3 problems while using openfast regarding aerodynamic loadings, it will be greatly appreciated if you can have the those solved.

Question1:
I have a problem when calculation the yaw bearing loads the 15MW NREL reference turbine in a parked condition(wind speed is 50 m/s), I’m investigating the loads of six dofs, but there is a significant difference between the the YawBrMyn and RtAeroMyh , YawBrMzn and Rt AeroMzh results in different wind propagating directions , small differences also occurred for Mx, while the results of Fx, Fy, agree quite well, similar phenomenon occurs for power generation conditions as well, it seems that the gravity contribution was considered for YawBr My, for the parked condition, I’d already turn off the dofs for blades and tower in elasdyn and switch the wake mode to 0 in areodyn, but I keep the default ShftTilt value. What else do I need to do the get the discrepancies eliminated? The results comparison is shown below (In the plots above, the labels for the x axis are wind propagation direction instead of angle of attack).
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Question2:
I want to provide wind loads acting on the blades and RNA for mooring analysis in a parked condition, which is performed in Orcaflex ( decoupled analysis), is it reasonable for me to use the YawBrXXn or AeroXXh results as illustrated above? And is the trend of results I reach above (RtAero results) varying with different angles of attack reasonable?

Question3:
If I want to take into account the wind load effect on the nacelle, how shall I model it in openfast?

Followings are my calculation files for the parked condition.

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image1920×844 236 KB

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image1146×1382 219 KB

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image1302×1354 281 KB

Best regards
Yajun

2

Dear Yajun,

Here are my answers to your questions:

  1. I would not expect the aerodynamic loads from the rotor as output from AeroDyn (RtAeroFxh, …, RtAeroMzh) to match the reaction loads at the yaw bearing as output from ElastoDyn (YawBrFxn, …, YawBrMzn). The former only include the contribution of aerodynamic loads on the rotor and the latter include the contributions of the aerodynamic loads and structural weight (even when all structural DOFs have been disabled). The coordinate systems are also different. Can you clarify what you mean by “wind angle of attack”? Do you mean the yaw error between the rotor shaft and wind direction?

  2. The answer depends on how the RNA is considered in the OrcaFlex model and whether structural DOFs are considered in the OrcaFlex model or not.

  3. OpenFAST does not currently support the calculation of aerodynamic loads on the nacelle; aerodynamic loads are only currently considered on the rotor and the tower. For a parked condition, the aerodynamic loads on the tower likely dominant over aerodynamic loads on the rotor, at least when the blades are feathered and the nacelle-yaw error is zero.

Best regards,