We compare three different computational fluid dynamics (CFD) software (based in the fine volume method) for validating a NACA airfoil, which can be used for example in the aerospace industry for an airplane's wing profile, and it can be used for example in the renewable industry for a wind turbine's blade or a water turbine's impeller profile. At the end of this paper, the result of our simulations will be compared with a validation case and the difference between the CFD software and the measured data will be presented.
2DN00: 2D NACA 0012 AirfoilValidation CaseThe purpose here is to provide a validationcase for turbulence models. Unlike verification, which seeks to establish that a model has been implementedcorrectly, validation compares CFD results against data in an effort to establish a model'sability to reproduce physics. A large sequence of nested gridsof the same family are provided here if desired. Data are also provided for comparison.For this particular "essentially incompressible" NACA 0012 airfoil case, the data are from experiments.For the purposes of this validation, the definition of the NACA 0012 airfoilis slightly altered from the original definition so that the airfoil closes at chord=1 with a sharp trailing edge.To do this, the exact NACA 0012 formulay= +- 0.6*[0.2969*sqrt(x) - 0.1260*x - 0.3516*x2 + 0.2843*x3 - 0.1015*x4]is used to create an airfoil between x=0 and x=1.008930411365 (the T.E. is sharpat this location). Then the airfoil is scaled down by1.008930411365. Thus, the resulting airfoil is a perfect scaled copy of the 0012, with maximum thickness of approximately 11.894% relativeto its chord (the original NACA 0012 has a maximum thickness of 12% relative to its blunted chord, but it, too,has a maximum thickness of 11.894% relative to its chord extended to 1.008930411365).The revised definition is:y= +- 0.594689181*[0.298222773*sqrt(x) - 0.127125232*x- 0.357907906*x2 + 0.291984971*x3- 0.105174606*x4]A set of surface points that have been defined using this altered formula are provided here, if desired:n0012points_superbig_clust_fix.dat.NOTE: Prior to 6/23/2014, there was a typo in the original scaled formula provided on this page. It was written:y= +- 0.594689181*[0.298222773*sqrt(x) - 0.127125232*x- 0.357907906*x2 + 0.291984971*x3- 0.105174696*x4] (typo underlined).With the typo, there was a slight order 10-8non-closure at the trailing edge (T.E.) (and very small influence throughout). At this time, the provided grids in the link below have used the incorrect formula and were closed at the T.E. by setting y to beexactly 0 at x=1. However, the influence of the typo is insignificant.Note that the grids supplied in the link below are considered to be appropriate for thelevel of validation explored here, but are likely not fine enough when high accuracy is required. Convergence properties ("goodness" ofresults as a function of grid size) are explored in more detail with different grid families inNumerical Analysis of 2D NACA 0012 Airfoil Validation Case.The finer grids on the "Numerical Analysis" page also include the correction in the scaled NACA 0012 formula.The turbulent NACA 0012 airfoil case should be run atessentially incompressible conditions (the recommendation here is to run M = 0.15 in compressible CFD codes).The Reynolds number per chord is Re = 6 million.Boundary layers should be fully turbulent over most of the airfoil.Inflow conditions for the turbulence variables should be reported.To minimize issues associated with effect of the farfield boundary (which can particularlyinfluence drag and lift levelsat high lift conditions), the farfield boundary in the grids provided have been located almost500 chords away from the airfoil. Otherwise, a "farfield point vortex" boundarycondition correction should be employed (see Thomas and Salas, AIAA Journal 24(7):1074-1080, 1986, ).The following plot shows the layout of the provided NACA 0012grids, along with typical boundary conditions.(Note that particular variations of the BCs at the farfield boundariesmay also work and yield similar results for this problem.)
Download Theory of Wing Sections Including a Summary of Airfoil Data
The Abbott and von Doenhoff data (Abbott, I. H. and von Doenhoff, A. E., "Theoryof Wing Sections," Dover Publications, New York, 1959) were not tripped.The Gregory and O'Reilly data (Gregory, N. and O'Reilly, C. L., "Low-SpeedAerodynamic Characteristics of NACA 0012 Aerofoil Sections, including the Effectsof Upper-Surface Roughness Simulation Hoar Frost," R&M 3726, Jan 1970)were tripped, but were at a lower Re of 3 million. Lift data are notaffected too significantly between 3 million and 6 million, but drag data are (e.g.,according to McCroskey, tripped CD,0 at Re=3 million is about 10% higherthan tripped CD,0 at Re=6 million).The Ladson tripped data (Ladson, C. L., "Effects of Independent Variation of Mach andReynolds Numbers on the Low-Speed Aerodynamic Characteristics of the NACA 0012Airfoil Section," NASA TM 4074, October 1988, ) appear to be the most appropriateof these data sets for comparison with fully turbulent CFD forces at Re=6 million. For comparing with surface pressure coefficients, data of Ladson et al (Ladson, C. L., Hill, A. S., and Johnson, Jr., W. G., "PressureDistributions from High Reynolds Number Transonic Tests of an NACA 0012 Airfoil inthe Langley 0.3-Meter Transonic Cryogenic Tunnel," NASA TM 100526, December 1987, )do not appear to resolve the leading edge upper surface pressurepeak well. Gregory and O'Reilly CP data (at Re=3 million) appear to be better resolved.The Gregory and O'Reilly data also show some noticeable differencesfrom the Ladson et al pressure data levels over the front half of the airfoilat alpha=10 and 15.It is believed that the Gregory data are likely more two-dimensional and hence more appropriatefor CFD validation of surface pressures.
This app queries an aerodynamic database of NACA 4 digits, 5 digits, 6 series, and NASA supercritical airfoils. Data for the NACA sections has been derived from the book Theory of Wing Sections, by Abbott and Von Doenhoff. Data for NASA supercritical (cambered) airfoil is extracted from NASA TM 81912. The app reports airfoil characteristics, lift curve and drag polar with a few inputs. The user has only to select airfoil family and assign relative thickness and Reynolds number. The characteristics of the curves are reported in a table, which can be exported on a spreadsheet file. All data are at low Mach number, incompressible flow regime. Very useful in preliminary aircraft design, when the user needs a reliable source of data but has only few global parameters to play with. 2ff7e9595c
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