Large Eddy Simulation of the Flow around a High-Lift Airfoil

Doctoral thesis, 2003

The work presented in this thesis concerns the efforts of conducting a Large Eddy Simulation (LES) around an airfoil. The airfoil is close to stall, near maximum lift and the Reynolds number is high. In the flow a transitional separation bubble is present. With the aim of solving the flow around an aeroplane, wing or profile at aeronautical conditions, the meshes become inevitably coarse (even for the Aerospatiale A-profile studied in this thesis) and the near-wall region cannot be resolved. The thesis investigates different ways of modelling the near-wall region: by using wall-functions or by using RANS close to the wall. As a result of using coarse meshes, numerical problems arise in the form of unphysical wiggles. This problem is particularly severe in the airfoil flow with its thin laminar boundary layer. In the thesis a wiggle-detector scheme has been used and other ways of treating the laminar region are investigated (by modifying the SGS-models and the spatial schemes). It is found that the treatment of the laminar region has a major effect on the turbulent boundary layer further downstream. The thesis also discusses the requirements on the resolution when the near-wall region is (or should be) modelled and tries to see the benefits of using a Large Eddy Simulation in such simulations.