Dynamic Stall Theory and Implementation

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Marc.Winter
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Re: Dynamic Stall Theory and Implementation

Postby Marc.Winter » Thu Oct 31, 2019 1:44 am

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
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Re: Dynamic Stall Theory and Implementation

Postby Marc.Winter » Mon Nov 04, 2019 11:53 am

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
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Re: Dynamic Stall Theory and Implementation

Postby Emmanuel.Branlard » Tue Nov 05, 2019 10:58 am

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
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Re: Dynamic Stall Theory and Implementation

Postby Marc.Winter » Tue Nov 05, 2019 11:25 am

Hi Emmanuel

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


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