Revisiting LESFOIL: Wall-resolved LES of Flow Around an Airfoil at Re_c = 2.1 × 10~6

摘要

This paper investigates an airfoil flow involving a turbulent transition and separations near stall condition at a high Reynolds number Re_c = 2.1 × 10~6 (based on the freestream velocity and the airfoil chord) and provides the wall-resolved LES database for near-wall model in LES by conducting wall-resolved LESs. The same flow conditions and airfoil as the LESFOIL project are employed. The present results are compared with the exiting experimental and numerical data. The LES with the finest mesh (△_ε~+ ,△_η~+,△_ζ~+: chordwise, wall normal, spanwize ≲ 25,0.8,13) and the widest spanwise extent (approximately 5% of the chord length) resolves the key phenomena of the flow (i.e., laminar separation, transition to turbulence, turbulent reattachment, turbulent boundary layer development, and turbulent separation) and well predicts mean statistics. The obtained database indicates that the pressure-gradient term in the mean streamwise-momentum equation is not negligible at the laminar and turbulent separated regions. This fact suggests that widely used equilibrium wall model is not sufficient and the inclusion of the pressure-gradient term is necessary for wall modeling in LES of such airfoil flow. Additionally, influences of computational mesh resolution and spanwise extent on the computational results are investigated. The LES using a coarse mesh underestimates the laminar and turbulent separated regions by numerical dissipation, and leads to a loss of the unsteady features. On the other hand, the LES using a short spanwise extent enforces the turbulent transition near the leading edge to be two-dimensional states and overestimates the separated region near the trailing edge by a spurious two-dimensional large-scale vortex.