Spanwise blade forces

Hi all,

I am currently looking at the force distribution along the blade of the NREL 5MW turbine. The model is set to work at rated and steady conditions of 11.4m/s and 12.1rpm, and ran both ElastoDyn and BeamDyn with AeroDyn15. I plotted FN and FT using, respectively:

“B1N1Fn, B1N2Fn, B1N3Fn, B1N4Fn, B1N5Fn, B1N6Fn, B1N7Fn, B1N8Fn, B1N9Fn”
“B1N1Ft, B1N2Ft, B1N3Ft, B1N4Ft, B1N5Ft, B1N6Ft, B1N7Ft, B1N8Ft, B1N9Ft”

Making sure that N9 is in fact the last node of the mesh.

As found in literature (but please correct me if I’m wrong anywhere in this post) I would have expected the forces to peak at around 0.8-0.9R, and drop close to zero in proximity of the blade tip. Instead, as shown below:

NO tip loss: the forces in FAST decrease only just slightly (but not as much as I thought they would)
INCLUDING tip loss: FT increases instead of dropping, and peaks at the tip

Similar plots are obtained with forces on the rotor plane, Fx and Fy. Could you explain this behaviour?

Many thanks for your help.

Best regards,

Daniel
No_Tip_Loss.png
Tip_Loss.png

Dear Daniel,

Are you using FAST v8.16 or OpenFAST v1.0.0 or something else? As explained in the OpenFAST v1.0.0 ReadMe file (wind.nrel.gov/nwtc/docs/README_OpenFAST.pdf), AeroDyn v15 was improved a lot between FAST v8.16 and OpenFAST v1.0.0.

Best regards,

Dear Jason,

Thank you for your quick response.

I used FAST v8.16 - will switch to OpenFAST and re-run the cases.

Best regards,

Daniel