Prediction of a thin-airfoil stall phenomenon using les/rans hybrid methodology with compact difference scheme

Prediction of a Thin-airfoil stall phenomenon of NACA64A006 airfoil is numerically investigated using Large-Eddy Simulation (LES)/ Reynolds-Averaged Navier-Stokes (RANS) hybrid methodology with highorder compact differencing scheme. Subsonic flow of M∞ = 0.17 with the high Reynolds number of Re = 5.8 × 106 is considered and the angle of attack is varied from 4.0° through 11.0°. The computed results are compared with the experiments of McCollough and Gault. Thin-airfoil stall phenomenon is generally characterized by the laminar flow separation at the leading edge and the turbulent reattachment, where the reattachment point gradually moves rearward with increasing angles of attack. Simulations of such phenomenon are considered to be one of the challenging cases for the Computational Fluid Dynamics (CFD). Thin-airfoil stalling aerodynamic characteristics are successfully predicted using the LES/RANS hybrid methodology with high-order compact difference scheme with less costly than pure LES approaches. For the prediction of thinairfoil stall phenomenon, it is necessary to properly resolve the short bubble near the leading edge and the short-to-long bubble transition where suction pressure peak collapses with increasing angles of attack. From the instantaneous and time-averaged flows, it is confirmed that the short bubble near leading edge is a phenomenon that appears when the unsteady small vortices shedding from the leading edge is averaged for a certain time length. The high-order compact differencing scheme provides extremely high fidelity results of the complicated and separated flowfields associated with a NACA64A006 airfoil near stall even under the reasonable number of grid points. Thin-airfoil stall characteristics are well predicted with the numerical transition method implemented in the original Baldwin and Lomax turbulence model which detects the transition point automatically from the computation. The LES/RANS hybrid methodology with the simple transition method is considered to be an effective prediction tool for this kind of flows where transition points should be determined by the computation.