by Dr. David J. Laino
Airfoil data are rarely available for angles of attack over the entire range of ±180°. This is unfortunate for the wind turbine designer, because wind turbine airfoils do operate over this entire range. The AeroDyn routines require the user to provide airfoil data tables over the entire range so that it will be able to analyze any combination of wind speed, rotor speed, wind direction and yaw angle. If a table is not provided over the complete range, and an unusual angle of attack is encountered during the calculations, the program will terminate with an error message.
Fortunately, the aerodynamic characteristics of an airfoil generally become independent of the airfoil sec-tion shape for very high positive or negative angles of attack. This makes it possible to extrapolate from wind tunnel data (for the particular airfoil) to flat-plate characteristics for angles of attack near ±90°. The flat-plate lift and drag characteristics depend only upon the aspect ratio of the plate.
The FoilCheck program is a simple utility program that helps the user create an airfoil data table for AeroDyn-based simulators. It performs the following major functions:
FoilCheck requires the user to start with a data file in the AeroDyn format. All static airfoil characteristics of the airfoil that are known to the user must be contained in the input file. The static data need not cover the angles between ±180°. Dummy values for the dynamic stall characteristics must also be in the file as place holders.
CAUTION: The program assists the user in creating an airfoil data file. The process still requires accurate input data and judgment by the user. It does not completely automate the process of creating accurate data files. The user is prompted for inputs that require engineering judgment and, sometimes, a bit of guess-work. It is very important that the user check the resulting data file to be certain it is credible. This is one of the most important and difficult steps in creating an accurate AeroDyn model of a turbine. We hope that FoilCheck eases the burden of creating the data files in the necessary format, but we know it cannot ease the burden of ensuring the data are accurate. The importance of accurate airfoil data cannot be overstressed. We encourage all users to devote considerable energy to locating airfoil data that is appropriate for the Reynolds number and surface roughness that will be seen on the turbine. The list of references at the end of Appendix D in the AeroDyn User's Guide contains several sources of data for wind turbine airfoils over an extended range of angle of attack. Furthermore, extrapolation cannot be as accurate as test data. The accuracy of your turbine simulation is highly dependent upon accurate airfoil characteristics.
If you want to make changes or need to compile to port FoilCheck to another platform, you will need to include AeroMods.f90 and GenSubs.f90 from the AeroDyn archive.
This program assumes the user is an experienced wind turbine aerodynamics analyst. Questions about this software should be directed to Dr. David J. Laino at Windward Engineering.
This program is documented Appendix D of the AeroDyn 12 User's Guide. You need the Adobe Acrobat Reader™ v3.0 or later to view or print it. If you do not have the latest version of the freeware Acrobat Reader, you can download it from Adobe.
This is a self-extracting archive of FoilCheck. Simply execute it in an appropriate directory to extract the files. It contains the change log, the source code, sample data file, and PC executable. We compiled the souce code with Compaq Visual Fortran® v6.6.A.
This material was prepared as an account of work sponsored by the National Renewable Energy Laboratory, a Division of Midwest Research Institute, in support of its Contract No. DE-AC36-98-GO10337 with the United States Department of Energy. Neither the National Renewable Energy Laboratory, the United States Government, nor the United States Department of Energy, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights.
The software is distributed for evaluation purposes only. Feedback concerning the validity of the software should be provided to the authors.
If you want to refer to the FoilCheck website in a report, here is a reference you can use:
NWTC Design Codes (FoilCheck by Dr. David J. Laino). http://wind.nrel.gov/designcodes/preprocessors/foilchk/. Last modified 10-May-2005; accessed 10-May-2005.
This page was generated by createpage.pl on 10-May-2005 at 15:21:41.
Questions about the NWTC Design Codes web pages? Contact Marshall Buhl.
The National Wind Technology Center is operated by the National Renewable Energy Laboratory (NREL), a national laboratory of the U.S. Department of Energy.