RANS and LES/RANS Simulation of Airfoils under Static and Dynamic Stall

This work presents results from Reynolds-averaged Navier-Stokes and hybrid Largeeddy/Reynolds-averaged Navier-Stokes (LES/RANS) simulations of two flow cases: a turbulent flow past an Aerospatiale A-Airfoil near stall at a chord Reynolds number, ( , , ), and a flow past NACA 0012 airfoil under static and dynamic stall conditions ( , , ). In the flow past the A-Airfoil, the suction side boundary layer is complex: it includes a laminar separation bubble by an adverse pressure gradient, a turbulent reattachment and a turbulent separation near trailing edge. Comparisons with surface skin-friction coefficient and pressure coefficient distribution are generally in good agreement with experimental measurements. Comparisons with experimental velocity profile data and Reynolds-stress data are also generally favorable. Leading-edge laminar separation and turbulent reattachment is predicted when the Menter-Langtry correlation-based transition model is used in combination with either RANS or LES/RANS strategies, but the level of trailing-edge separated is under-predicted, relative to experimental data and to results obtained without the transition model. In the flow past NACA 0012 airfoil case, the airfoil was dynamically pitched about its quarter-chord at a reduced frequency, . Computational results from RANS simulations show that the flow remains attached in the leading edge region above the static stall angle during upstroke, whereas it remains separated below the static stall angle during downstroke. These results match the experimental measurement well. For static stall case of flow past NACA 0012 airfoil, results from the LES/RANS simulation are in much better agreement with the experimental data compared with those from RANS simulations. The RANS models predict flow attachment at the leading edge, whereas the LES/RANS model predicts leading edge flow separation, with the leading-edge vortex stabilized upstream of the trailing edge.