Technical Validation Report: Aerodynamic Analysis of the S823 Airfoil

Project ID: CFD-S823-VAL-2026

Prepared For: Aerodynamic Design Review

Date: April 16, 2026

1. Executive Summary

This report details the computational fluid dynamics (CFD) validation of the NREL S823 airfoil, a profile specifically designed for wind turbine applications requiring high lift and stall regulated performance. The study utilizes a high-fidelity structured mesh generated in ANSYS ICEM CFD and a pressure-based solver in ANSYS Fluent. Results were validated against XFoil data at a Reynolds number of $1.05 \times 10^6$.

2. Computational Domain & Geometry

  • Airfoil Profile: S823 (Root/Thick Airfoil)

  • Chord Length ($c$): 0.63 m

  • Domain Type: C-Grid Topology

  • Domain Extent: 15c upstream and 25c downstream to ensure undisturbed far-field conditions.

3. Meshing Strategy (ICEM CFD)

To ensure high accuracy in the boundary layer, a Structured C-Grid was utilized.

  • Blocking Topology: O-grid refinement around the airfoil surface to maintain orthogonality.

  • Wall Spacing: Initial cell height was set to $1.5 \times 10^{-5}$ m to achieve a $y+ \approx 1$, ensuring the viscous sublayer is fully resolved.

  • Quality Metrics: * Max Skewness: 0.16 (Excellent)

    • Determinant Quality: > 0.95

  • Grid Independence: The final mesh contains approximately 120,000 hexahedral elements, a density determined to be mesh-independent for $C_l$ and $C_d$ accuracy.

4. Physics & Solver Setup (ANSYS Fluent)

  • Solver: Pressure-Based Steady State

  • Turbulence Model: $k-\omega$ Shear Stress Transport (SST) with Intermittency Transition modeling.

  • Fluid Properties (Air):

    • Density: 1.225 $kg/m^3$

    • Dynamic Viscosity: $1.7894 \times 10^{-5}$ $kg/m\cdot s$

  • Boundary Conditions:

    • Inlet Velocity: 24.28 m/s

    • Angle of Attack ($\alpha$): $4^\circ$

    • Outlet: Pressure Outlet (0 Pa gauge)

5. Results & Discussion

5.1 Convergence Monitoring

Convergence was achieved within 500 iterations. Residuals for continuity, momentum, and turbulence parameters dropped below the $10^{-6}$ threshold. Force monitors for Lift ($C_l$) and Drag ($C_d$) showed stable, horizontal asymptotes.

5.2 Aerodynamic Coefficients

The following table compares the Fluent CFD results with XFoil baseline data:

ParameterCFD (Fluent)XFoil Baseline% DeviationLift Coefficient ($C_l$)1.1521.1550.26%Drag Coefficient ($C_d$)0.01580.01523.94%Moment Coefficient ($C_m$)-0.064-0.0651.53%

5.3 Flow Visualization

  • Pressure Distribution: A strong suction peak is observed at the leading edge ($x/c \approx 0.05$), consistent with the high-lift nature of the S823.

  • Velocity Magnitude: Streamlines remain attached across the upper surface, with a thin wake formation observed at the trailing edge.

6. Conclusion

The numerical simulation of the S823 airfoil demonstrates excellent agreement with validated aerodynamic data. The structured ICEM mesh provided superior convergence stability, and the Fluent $k-\omega$ SST model accurately captured the lift characteristics. This setup is verified for further use in multi-element or variable AoA studies.

End of Report