Hybrid turbulence model simulations of partially stalled airfoil flow

The modified NACA 64₃-618 airfoil of the Aeromot 200S Super Ximango motorglider was chosen for wing section simulations at Re = 300;000 and a = 15 deg. A coarse-grid direct numerical simulation was carried out to obtain detailed reference data. A laminar separation bubble close to the leading edge causes transition to turbulence of the suction-side boundary layer. The turbulent boundary layer separates near midchord. The considerable computational expense of this simulation provided the motivation for hybrid simulations based on the k-? model and a one-equation renormalization group model. An extension to the turbulence models that "seeds" synthetic turbulence velocity fluctuations in the parts of the flowfield where the grid resolution changes is proposed but was found to have little effect on the mean flow. When the model contribution was too low, the turbulent boundary layer on the airfoil suction surface separated too early. By increasing the model contribution, a reasonable agreement with the reference data was obtained.