Wall-resolved LES investigation of Reynolds number effects on a near-stall airfoil flowfield up to Re_c=10⁷

We have conducted a wall-resolved LES around the Aerospatiale A-airfoil at Re_c=10⁷ to understand the Reynolds number effects of the trailing-edge stall phenomena and to construct turbulence databases at a high Reynolds number (https://www.klab.mech.tohoku.ac.jp/database/). The computational grid contains approximately 38 billion grid points, and the simulation is conducted by the supercomputer Fugaku. Compared to the prior LES at Re_c=2.1x10⁶ [Asada & Kawai, Phys. Fluids (2018)], the present LES shows typical Reynolds number effects, such as the delay of the turbulent separation and the earlier turbulence transition. We analyze the development of the boundary layer over the upper airfoil surface through the integral relation as in the prior study [Tamaki et al., Phys. Rev. Fluids (2020)] to clarify the causes of the Reynolds number effects. The analysis shows that the primary difference in the boundary layer thickness is caused in the laminar and transitional regions, and then the difference is amplified in the downstream region.