Crystal Journal of Materials Science & Engineering - Article In Press

Abstract
This study presents a transition-model-based comparative computational investigation of four symmetric NACA airfoils (0012, 0015, 0018, and 0020) operating at low Reynolds numbers ranging from 3×10⁵ to 1×10⁶. In this flow regime, transitional effects such as laminar separation and delayed boundary-layer transition significantly influence aerodynamic performance. A two-dimensional steady Reynolds-Averaged Navier–Stokes (RANS) framework was employed using the SST k–ω turbulence model coupled with the γ–Reθ transition model to improve the prediction of lift and drag characteristics under low-Reynolds-number conditions. A structured C-type mesh with near-wall refinement was generated to ensure accurate boundary-layer resolution. Numerical results were validated against available experimental data, demonstrating good agreement in aerodynamic performance trends within the pre-stall region. The results indicate that aerodynamic efficiency increases with Reynolds number for all profiles due to delayed flow separation and enhanced boundary-layer stability. Among the airfoils investigated, NACA 0012 consistently exhibited the highest lift-to-drag ratios at moderate angles of attack (6°–9°), whereas thicker profiles such as NACA 0018 and 0020 showed comparatively lower aerodynamic efficiency. This work provides a transition-aware comparative assessment of multiple symmetric NACA airfoils across a practical low-Reynolds-number range relevant to small-scale wind turbines and unmanned aerial vehicle (UAV) applications. The findings highlight the importance of airfoil selection where transitional flow effects play a critical role in aerodynamic performance.

Keywords
NACA Airfoils, Reynolds Number, Aerodynamic Performance, Turbulence Model