Comparative Analysis of Flow Fields Around NACA 23012 Airfoil at Three Characteristic Angles-of-Attack

Flow fields around the airfoil NACA 23012, developed over 80 years ago but still much employed, at Mach number M = 0.18 and Reynolds number Re = 1.8 million were experimentally and numerically investigated. Three different characteristic angles of attack (AoA) were selected. The angle includes a zero-degree AoA where drag is minimal, optimal AoA where the lift-to-drag ratio is maximal, and critical AoA where the lift is maximal. These selections are made to understand better the main flow features such as transition, flow separation, (unsteady) wake behavior, and turbulent structures appearing around the airfoil, as well as to investigate the possibilities of their modeling. Two principally different numerical approaches were employed: Reynolds-averaged Navier-Stokes (RANS) equations vs. wall-modelled large eddy simulation (WMLES). Both results were compared to recent experimental data. In both cases, the computational domain was the same (circular, spanning 0.2 chord length in spanwise direction), and the two generated meshes are comparable, particularly in the vicinity of the wall. Values of velocity and pressure were assigned to the outer boundaries, and sides were periodic. In contrast, airfoil walls were treated differently depending on the solver (no-slip vs. algebraic equilibrium wall model). Excellent correspondence between global results (aerodynamic coefficients) was achieved, particularly at lower AoAs. However, it was found that in order to accurately predict flow behavior at critical AoA and to capture the main turbulent structures, WMLES should be utilized.