NREL 5MW WT: FAST x GH Bladed deflections comparison

Hello everyone,

My attempt here is to have a reliable physical implementation of the NREL 5MW Baseline WT on GH Bladed so I can work with the development of load reducing measures using different control strategies implementations.

My biggest concern is this particular set of deflections that are found to be way different from the validation results shown in the document. I already verified all the stiffness and geometry of the blades more than once and I’m also using some implementation made available by TU Delft as a part of the UPWIND project.

Where “OoPDefl1” refers to the out-of plane tip deflection of Blade 1 relative to the undeflected blade-pitch axis.

All the other parameters shown in the document are fairly identical to the obtained with the same model used.

I would love to have any insights about the different methods used for this calculation in the different codes and any possible reason for this difference in the results.

Best Regards,

Vitor Ramalho.

Dear Vitor,

Those results look quite different. This tells me that the models are predicting different thrust or different blade stiffness. You can compare the former by examining rotor thrust or tower fore-aft shear force. You can compare the later by comparing the natural frequencies.

Best regards,

Dear Jason,

In the first case, does the rotor thrust and tower fore-aft shear force represent the same behavior to be observed? I found relatively large gap here, is there a particular reason for this?

In the second case, I really couldn’t differentiate all the modes described in the baseline document, but found some to be really close. The tower and blades modes seem to be inside of the expected, at least for the 1st values described.

Would you blame all the erratic behavior on the thrust or the frequencies have a part on it?

Thank you again for any insights.

Best Regards,

Vitor Ramalho.

Dear Vitor,

Regarding the offset in rotor thrust between FAST and GH Bladed, my guess is much of this offset is related to the rotor weight term included in the FAST result, as discussed in the following forum topic: http://forums.nrel.gov/t/the-effect-of-tilt-angle/769/1.

The first three blade frequencies you are reporting from GH Bladed are very close to FAST results reported in Table 9-1 of the NREL 5-MW specifications report.

That leaves me puzzled as to why GH Bladed is showing less steady-state deflection than FAST.

Best regards,

Dear Jason,

Thank you very much for you help discussing those points with me.

I’ll keep working on this model. since my work benefits from qualitative results.

I would appreciate any insights that may come in the future.

Best Regards,

Vitor Ramalho.