Experimental and Numerical Investigation of Stall on the NACA

In this paper, measurements of the stall of a NACA 64(3) – 418 airfoil section are presented and compared to a simulation with a hybrid Reynolds-averaged Navier–Stokes (RANS)/large-eddy simulation (LES) model with the goal of gaining deeper insight into the flow physics of a stall cell and the turbulent wake in such conditions. Detailed measurements of the evolution of the velocity deficit and turbulence within the wake along with surface pressure measurements and flow visualization provided a comprehensive database for code validation and flow physics studies. The measurements in the Laminar Wind Tunnel of the Institute of Aerodynamics and Gas Dynamics were performed at a Reynolds number of 2.5⋅106 and comprised surface pressures, oil flow surface visualizations, and hot-wire measurements of the wake. The results at α=15° were used as validation data for a hybrid RANS/LES run at the same flow conditions. It was shown that the Bernoulli-based detached eddy simulation (BDES) model, which uses a shielding function based on a localized Bernoulli formulation, combined with effective gray area mitigation can capture the stall cell pattern and the point of flow separation at an angle of attack of α=15°. Furthermore, the velocity deficit and the Reynolds stresses in the wake show good agreement between simulation and experiment under these conditions.