Limiting value of Reynolds Averaged Simulation in numerical prediction of flow over NACA4415 airfoil

Reynolds Averaged Simulation (RAS) and Large Eddy Simulation (LES) are two widely used turbulence modeling approaches in Computational Fluid Dynamics (CFD). RAS simulations require less computing times than used by LES. When large eddies of flow become dominant, RAS simulations cannot predict accurate results. Hybrid RAS-LES approach is effective solution to reduce computational cost and time. In this approach, only parts of flow where larger eddies become dominant are solved using LES, and other areas are resolved using RAS. In order to apply RAS-LES hybrid models, regions of flow where RAS simulation cannot be applied need to be identified. The present work finds the limiting value of angle of attack for a NACA4415 airfoil where RAS simulation can be applied. Simulations were performed using two widely used RAS turbulence models for angles of attacks ranging from -6 to 16.3 degrees. Then results are compared against experimental data. It is found that for NACA4415 airfoil at a Reynolds number of 1.5 million, RAS simulation can be used to successfully predict flow behavior up to an angle of attack of 4.1 degrees. Based on this limiting angle of attack, an approach is suggested for hybrid RAS-LES simulation for a wind turbine.