Polar dependencies at different Reynolds Numbers

Wind & Water Airfoils
1

Dear NREL-Community,

I want to determine the static stall of an airfoil for different Reynolds numbers. To change the Re number I have changed the wind speed.

StaticStall_diff_RE
StaticStall_diff_RE1920×1177 119 KB

However, as can be seen in the picture, the larger Re number does not change the static stall at the airfoil. This is not plausible.

I assume that static stall depends on the polar dependencies (cl, cd, cm, and aoa) that have already been defined in a pre-processor.

My question:

How can I determine the polar dependencies of a airfoil for a given RE number? I am aware that XFOIL is a tool that calculates this. However, XFOIL does not converge for the examined airfoil at high Re numbers, e.g. Re=10e6-20e6. Are there any other tools I can use to determine the polar dependencies at high Re numbers?

Airfoilprep from Wisdem and the pythontoolbox in Openfast unfortunately only allow manipulation of the polar information, but no determination of the polar dependencies (cl, cd, cm and aoa).

I am looking forward to your answer and thank you in advance!

Best Regards,
Jason

2

Dear @Jason.Printezis,

Perhaps you need to consider using 2D or 3D airfoil-shape resolved CFD?

Best regards,

3

Dear @Jason.Jonkman ,

thanks a lot for the answer!

How is this handled in Openfast? Are the polar dependencies in the airfoil files in Aerodyn calculated by CFD?

Best regards,
Jason

4

Dear @Jason.Printezis,

The generation of airfoil polar data is a pre-processing step for the AeroDyn module of OpenFAST and AeroDyn is not tied to specific pre-processing approach. That is, you could use XFoil, wind tunnel tests, CFD, etc. to derive the airfoil polar data for use by AeroDyn. Typically tools such as AirfoilPrep / AirfoilPreppy are used to take 2D airfoil polar data at low angles of attack (from XFoil, wind tunnel tests, CFD, etc.) and apply 3D rotational augmentation corrections and extrapolations to obtain the airfoil polar data over the full 360-deg range of angle of attack before using such data within AeroDyn. It is also possible to use an inverse-BEM approach to derive airfoil polar data inclusive of 3D rotational augmention from blade-resolved CFD.

Best regards,

1 Like
5

Dear @Jason.Jonkman,

all clear, thanks a lot again!

Best regards
Jason