DETACHED AND LARGE EDDY SIMULATION OF AIRFOIL FLOW ON SEMI-STRUCTURED GRIDS

摘要

This study aims at investigating the flow around a NACA 4412 airfoil at high Reynolds numbers and moderate angles of attack on semi-structured grids, which allow for a blockwise grid refinement in areas of physical interest (e.g. walls). Unlike other configurations using Large Eddy Simulation (LES), this flow features only a small pressure-induced separation bubble at the trailing edge of the profile showing no massive transient motion. Therefore, this flow is very sensitive to both spatial resolution, which might not be sufficient in case of wall-resolving LES, and the employed subgrid-scale model, which has to capture all relevant unresolved motion in the transitional boundary layer on the suction side. Since wall-resolving LES remains rather unfeasible for flows at Reynolds numbers beyond Re = 10~6 in the near future, the method of Detached Eddy Simulation (DES) has recently attracted high interest. DES avoids the high near-wall resolution by applying the Reynolds-Averaged Navier-Stokes equations method (RANS) in the vicinity of the wall and a modified Spalart-Allmaras one-equation turbulence model in the far field. In the overlap region, this model blends automatically from a statistical to a subgrid-scale model without the use of shape functions. The results of the flow around a square cylinder, used for a basic comparison, and the airfoil show a very good agreement with the experimental data, while only using a fraction of the numerical resources compared to an adequately resolved LES.