I was wondering if anyone is in possesion of the original 2D data of the profiles (“DU-airfoils”) used for the NREL 5 MW (not the 3D modified data which i found in the document “Defintion of a 5-MW Reference Turbine for Offshore System Development”). I checked the referenced documents (“Dowec 6 MW Pre-Design” and “Aeroelastic Modelling of the LMH64-5 Blade”) but I could only find plotted data for the “DU-airfoils”. The links provided by Marshall in “where to find airfoil data” unfortunately didn’t help either. The reason I need the data is that our inhouse rotor code has a semi-empiric dynamic stall modell (originally developed for helicopter applications) which needs the original 2D data for developing an analytical description of the coefficients over the whole range of angle of attack . Eventually I’d like to compare our results to those available to verify our code.
Best Regards, Ludwig
I’ve attached the original (unmodified, 2D) airfoil data used for the NREL 5-MW baseline wind turbine that I obtained from Koert Lindenburg of ECN. My understanding is that the original 2D data is wind tunnel data between approximate -10 to +20 deg angle of attack. This data was then expanded to the full 360deg using ECN’s StC code.
2DAirfoilDataFiles.zip (15.4 KB)
thank you very much. That is exactly what I was looking for.
Best regards, Ludwig
thanks again for the data. While going through the data 3 question occured. Maybe you can help me out:
Over the whole span the aerodynamic twist is equal to the structural twist. To my understanding that means that all profiles must have an equal angle of zero lift but this is not the case looking at the profil data. (e.g. DU40–> -3,5°<alpha0<-3°; DU35–> -1,5°<alpha0<-1°).
For me structural twist (or geometric twist) is the difference in angle of incidence betwenn blade section and reference location (here blade tip).
Aerodynamic twist on the other hand is the difference in zero lift angle (between considered section and reference).
Maybe I have a different understanding of those definitions due to my helicopter background and you guys use some other type of definition.
Are there any rules to strake between the different profiles (I’m not sure if “strake” is the correct english term) what I mean is how to “interpolate” the airfoil geometry, how to get the cl,cd,cm values between profiles. Is the interpolation rule linear? And where do I know at what position I have the “actual” given geometry?
When I looked at the 2D data of the several airfoils I found some unusual high values for the cl slope over alpha (e.g. dcl/dalpha>3*PI/rad at alpha~0° for DU40). That is very surprising to me to have a slope 1.5 times higher than in thin airfoil theory for such a thick profile in the linear area and only looking at 2D data. I know you did not measure the data by yourself but maybe you have some informations which could help understanding?
I hope I am not bothering you with too specific questions, I just wanne be sure to approach the problem the right way?
Best Regards, Ludwig
Regarding your first question, here the definitions of the aerodynamic (AeroTwst) and structural (StrctTwst) twist that we use in FAST/AeroDyn (and in the NREL 5-MW turbine documentation):
AeroTwst - Rotation of the chordline of the airfoil relative to the zero-twist location, such that the blade pitch angle plus AeroTwst is the angle between chordline and the rotor plane (neglecting structural deflection such as elastic twist).
StrctTwst - Rotation of the principle elastic axis for edgewise bending of the airfoil relative to the zero-twist location, such that the blade pitch angle plus StrctTwst is the angle between principle elastic axis for edgewise bending and the rotor plane (neglecting structural deflection such as elastic twist).
So, AeroTwst and StrctTwst would be identical if the principle elastic axis for edgewise bending lied along the chordline.
Regarding your second question, there are some discussions about interpolating airfoil geometry versus interpolating airfoil data in the forum topic found here: http://forums.nrel.gov/t/airfoils-on-a-5m-diameter-turbine/346/1.
Regarding your third question, I agree that sounds strange, but I don’t have an answer.