Local Blade axis in AeroDyn and in ElastoDyn

Dear Members,

I started to use the FAST v8.16 with ElastoDyn and AeroDyn v15. The simulation has been done, and the results generally corresponds to my expectation. Even the ‘Spn5FLyb1’-like outputs of ElastoDyn seem reasonable (negative in my case). Only the edgewise forces of AeroDyn (e.g. B1N3Fy) are uninterpretable for me. According to OutlistParameters.xls this output is the ‘tangential force (to plane)’. In my understandnis this is the direction denoted with ‘y’ on Figure 4. of AeroDyn v15 User Guide. The problem is that I expected a negative value for B1N3Fy in my simulation (similar to ‘Spn5FLyb1’), but unfortunately I’ve got a positive value. I would like to ask you if B1N3Fy (and this family of outputs) is really pointed in the direction of ‘y’ axis of Figure 4.? Or is this y-direction correct in Figure 4.?

Regards,
Balazs

Dear Balazs,

As mentioned in the footnote for output BαNβFy in Appendix E of the draft AeroDyn v15 User’s Guide and Theory Manual, positive Fy is in the direction of rotation, opposite local y, by convention.

I hope that helps.

Best regards,

Dear Jason,

thank you for the quick respond! Indeed the footnote in the latest version of the AeroDyn v15 Manual includes Fy, too.

In this case I would be pleased if you could confirm an other suspicion. The label ‘Local Blade Coordinate System’ in Figure 4. is not the y-axis of the ‘local yb1’ axis of ‘Spn1FLyb1’ output (mentioned in the OutListParameters.xlsx). With different words: the ‘local blade’ axis is different in AeroDyn and ElastoDyn

Regards,
Balazs

Dear Balazs,

Yes, you’re correct. The “local blade” coordinate system in ElastoDyn is aligned with the local structural twist, as discussed e.g. in the following forum topic: http://forums.nrel.gov/t/discrepancy-in-loads-between-blade-root-and-local-spans/1091/1.

Best regards,

Dear Jason,

thank you for supporting me to process this huge amount of information. I really appreciate your efforts!

Regards,
Balazs