Dynamic stall simulation of a pitching airfoil under unsteady freestream velocity

Effects of horizontal oscillations of the freestream velocity superimposed on a pitch oscillating NACA0012 airfoil were investigated using Computational Fluid Dynamics (CFD). The SST k-omega model coupled with a low-Reynolds number correction was applied for Re approximate to 10(5), when the airfoil was undergoing dynamic stall. The main parameter Phi, the phase difference between the freestream oscillation and the airfoil oscillation, was varied from 0 to pi. The Phi variation resulted in several times amplitude dynamic loads when Phi <= pi/2 to several times damping dynamic loads for Phi > pi/2 where some dynamic stall loads were damped even below static stall load values. It was found that Phi variation was divided into two main ranges based on the values of the unsteady freestream velocity at dynamic stall. The load variation also appeared with some differences including the shape of the trailing edge vortex sheet before stall, the circulation of the dynamic stall vortex pairs, the critical angles, vortex growth time and the secondary lift peak location that are discussed in detail. (C) 2013 Elsevier Ltd. All rights reserved.