Is DES approach better than RANS approach for airfoil stall simulation?

Purpose. DES (Detached-Eddy Simulation) approach is theoretically a good way of taking advantage of the merits of both RANS (Reynolds Averaged Navier-Stokes) and LES (Large Eddy Simulation) approaches. For engineers, it is important to know for a certainty that this is really so. We take the problem of stall and show that DES approach is really good for two of three different types of NACA airfoils. In the full paper, we explain in detail what we did for the problem of stall; here we give only a briefing. Even though LES method is expected for massively separated flow, it is not satisfactory because of the enormous requirement of grid points for practical aviation flow with large Reynolds number. In DES approach, the Spalart-Allmaras turbulence model reduces to a RANS formulation near the wall, and to a subgrid model of LES away from the wall. It is found that: (1) before the stall, DES gets almost the same results as RANS for three airfoils; (2) near the stall, for NACA64A-006 and NACA63₁-012, DES results are much closer to experimental data than RANS; and for NACA63₃-018, they are almost the same because it is trailing-edge stall type with small separation region when the stall occurs.