Dynamic Stall Theory and Implementation

[Marc.Winter]

Thanks Jason. I will then try to compare the results for both approaches once I finished the implementation, provided I find the required model parameters.

[Marc.Winter]

Another question: in the FAST 8 documentation, the non-dimensional time constants T_alpha and T_q are multiplied by a factor of 0.75. The manual explains "Note that Leishman (2011) recommends the use of the factor 0.75 for Tα ( M ) and Tq ( M ) to account for three- dimensional effects not included in piston theory.". I would like to understand where this factor 0.75 comes from but I can't find that report. Are these 3D effects rotaional effects, i.e. coriolis force, or general effects also applicable for linear motion?

[Emmanuel.Branlard]

Hi Marc,

I believe this report is an internal report delivered by Leishman to NREL and I'm not sure if it can be publicly shared. I'm quoting below the part that mention this:

“Based on correlation studies with oscillating airfoil measurements, the value of the foregoing
time constant in the L-B model has been modified by multiplying by a factor of 0.75. Justification
for this change comes about by recognizing that piston theory is a one-dimensional theory and that
for a two-dimensional airfoil there will be “end effects” at the leading and trailing edges of the
airfoil.”

The problem is that there is no reference pointing to the correlation studies. Maybe this is something we can find by digging through the papers published by Leishman. But it seems that the effects captured here are 2D effects and not the 3D effects you mentioned. Hopefully that answers part of your question. Let us know if you find the reference from Leishman. Thanks!

[Marc.Winter]

Hi Emmanuel

yes, this answers my question that this factor is not a special property of rotational motion but generally applicable. Thank you!

[Matthias.Schmid]

Dear Jason,

unfortunately the link to the documentation of the unsteady aerodynamics model is not working any more. Could you provide a new link?

[quote="Jason.Jonkman"]
The implementation of the Beddoes-Leishman unsteady airfoil aerodynamics (UA) model of AeroDyn v15 is documented in the following draft report: https://wind.nrel.gov/nwtc/docs/UnsteadyAero_Manual.pdf (this is a draft report, and updates are in progress).
[/quote]

Thank you very much,

Matthias

[Jason.Jonkman]

Dear Matthias,

This draft report has now been officially published--see: https://www.nrel.gov/docs/fy20osti/66347.pdf.

Best regards,