Entry 05 // Aerodynamics
Aerodynamic Analysis of NACA Airfoils
Three NACA sections swept from −6° to 18° in ANSYS Fluent, including the part where the original coefficients were normalized to the wrong reference area and how I found and validated the correction.
1.0 Overview
Analyzed the NACA 0012, 4412, and 6418 profiles in ANSYS Fluent, simulating flow at angles of attack from −6° to 18° at a 20 m/s freestream. The objective was to evaluate lift and drag for each section, identify stall behavior, validate against thin airfoil theory at low angles, and analyze the deviations caused by viscous effects and separation at high angles.
2.0 Method
Geometry and domain
Airfoil geometries were defined from standardized coordinate data and imported into ANSYS DesignModeler. The computational domain extended 2 m from inlet to outlet, giving a 4 m² domain large enough to keep boundary effects from contaminating the separation behavior.
Meshing and solver
- Structured quadrilateral mesh with surface sizing on the airfoil
- Increased mesh density at the trailing edge to capture pressure and velocity gradients
- Steady-state, pressure-based, incompressible solver
- Air at ρ = 1.23 kg/m³, μ = 1.78×10⁻⁵ Pa·s, freestream 20 m/s
Parametric study
Angle of attack was parameterized through the Parameter Set module in ANSYS Workbench across nine evenly spaced increments, automating geometry adjustment while holding freestream conditions constant.
2.5 The correction
The originally reported coefficients were normalized against Fluent's default 1 m² reference area instead of the true ~25 mm chord. Every coefficient was rescaled by a factor of 40.1, then validated it independently against the Reynolds number, which works out to Re ≈ 3.4×10⁴ and lines up with the corrected magnitudes.
| Section | cl,max | Behavior at high incidence |
|---|---|---|
| NACA 0012 | 0.891 | Separates earliest, sharp lift breakdown past ~12° |
| NACA 4412 | 1.289 | Similar stall onset with better lift characteristics |
| NACA 6418 | 1.418 | Retains attached flow to 18° |
Not quoted: moment coefficients
The recorded moment coefficients are unreliable because Fluent's default moment center is the origin, not the quarter chord, and they remain uncorrected. They are deliberately not reported anywhere on this page.
3.0 Results
Lift. All three sections showed lift increasing with angle of attack up to a stall onset near 12°. The NACA 6418 produced the highest lift coefficient throughout.
Drag. Drag increased gradually with incidence and more sharply beyond 12°. The 6418 carried higher drag, consistent with its thicker profile.
Flow field. At low incidence all three sections showed attached flow with little separation. Higher up the sweep, the 0012 separated early above 12°, the 4412 delayed separation to about 15°, and the 6418 stayed attached at 18°. Pressure contours showed strong upper-surface suction peaks, highest on the 6418, which lines up with its lift advantage.
Against thin airfoil theory. At low angles all three agreed closely with thin airfoil theory. Deviations grew with incidence as viscous effects and separation took over, which is expected since thin airfoil theory is inviscid. The 6418 tracked theory across the widest range.
4.0 Conclusions
- NACA 6418 was the most efficient of the three, with the best lift-to-drag ratios, delayed stall, and stable behavior across the full sweep
- NACA 4412 offered balanced performance for moderate requirements
- NACA 0012 served as the baseline, with the earliest stall
Full report
Method, mesh, the reference-area correction, and corrected polars for all three sections.