### Missing data and AirfoilPrep data different than airfoil files

Posted:

**Sat Feb 22, 2020 12:51 pm**Hello,

My current research consists in simulating the GE 1.5-SLE wind turbine considering Cm in OpenFAST. As known, the airfoil files for this simulation (s818_2703.dat, s825_2103.dat and s826_1603.dat) only shows the 360 degrees values for Cl and Cd, so I used the AirfoilPrep to extrapolate the original airfoil data that has the Cm (found here: https://wind.nrel.gov/airfoils/Coefficients/) with the same Reynolds number and get the 360 degrees values for Cm.

Comparing the extrapolated result of Cl and Cd obtained and the 360 degrees Cl and Cd found in the OpenFAST files mentioned before, there are differences between them. The differences are greater from -180 to -10 and from 10 to 180 degrees. This led me to think that the Cm values found may be wrong, although within -10 and 10 degrees, the differences are usually smaller than 1e-2.

Using the AirfoilPrep sheet, i've directly used the original data as input in the "TableExtrap", ignoring the "3DStall" section, but then I tried using the 3DStall correction and it didn't showed better results.

Also, I don't know the "Max CD" value needed to extrapolate the data correctly. Changing this value changes the result significantly in the -180 to -10 and 10 to 180 degrees range. May this be the only source of this differences? Where can I find the correct value for s818, s825 and s826 airfoils?

I've attached here my AirfoilPrep sheets for every airfoil. At the TableExtrap tab, i've inserted a "difference" column that calculates the airfoil files data minus the extrapolated data so it's easier to visualize the difference. Hope you guys can help me.

PS: I know the Reynolds number from the s818 original data (Re max 3.5e6) isn't compatible with the data file of the OpenFAST (Re=4e6), but I attached here anyway.

Kindly,

My current research consists in simulating the GE 1.5-SLE wind turbine considering Cm in OpenFAST. As known, the airfoil files for this simulation (s818_2703.dat, s825_2103.dat and s826_1603.dat) only shows the 360 degrees values for Cl and Cd, so I used the AirfoilPrep to extrapolate the original airfoil data that has the Cm (found here: https://wind.nrel.gov/airfoils/Coefficients/) with the same Reynolds number and get the 360 degrees values for Cm.

Comparing the extrapolated result of Cl and Cd obtained and the 360 degrees Cl and Cd found in the OpenFAST files mentioned before, there are differences between them. The differences are greater from -180 to -10 and from 10 to 180 degrees. This led me to think that the Cm values found may be wrong, although within -10 and 10 degrees, the differences are usually smaller than 1e-2.

Using the AirfoilPrep sheet, i've directly used the original data as input in the "TableExtrap", ignoring the "3DStall" section, but then I tried using the 3DStall correction and it didn't showed better results.

Also, I don't know the "Max CD" value needed to extrapolate the data correctly. Changing this value changes the result significantly in the -180 to -10 and 10 to 180 degrees range. May this be the only source of this differences? Where can I find the correct value for s818, s825 and s826 airfoils?

I've attached here my AirfoilPrep sheets for every airfoil. At the TableExtrap tab, i've inserted a "difference" column that calculates the airfoil files data minus the extrapolated data so it's easier to visualize the difference. Hope you guys can help me.

PS: I know the Reynolds number from the s818 original data (Re max 3.5e6) isn't compatible with the data file of the OpenFAST (Re=4e6), but I attached here anyway.

Kindly,