INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS Int. J. Numer. Meth. Fluids 2011; 67:135–154 Published online 20 April 2010 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/fld.2332 Numerical investigation of turbulent flow over a stationary and oscillatory NACA0012 airfoil using overset grids method M. J. Vafaei Rostami 1, ∗, † , M. Saghafian 1, ‡ , A. Sedaghat 1, ‡ and Mo. Miansari 2 1 Mechanical Engineering Department, Isfahan University of Technology, Isfahan, Iran 2 Mechanical Engineering Department, Babol Noushirvani University of Technology, Babol, Iran SUMMARY In this numerical study, unsteady and incompressible turbulent flows have been considered around stationary and flapping NACA0012 airfoil. Overset grid technique is used in this work. Three turbulence models have been examined including the linear Launder–Sharma k –ε model, nonlinear Craft–Launder– Suga k –ε model and nonlinear Lien–Chen–Leschziner k –ε model. First, the flow field around a stationary airfoil is solved for validating purposes. The results reveal different capabilities of capturing separation angle of attack using linear and nonlinear models. Nonlinear models predict smaller stall angle compared with the linear ones. Second, the flow field around a plunging airfoil is considered at various angles of attack, reduced frequencies and different amplitudes. The results show that the effects of reduced frequency are highly significant. There are differences in aerodynamic forces and wake structures in the upstroke and the down stroke motions, because they are functions of the mean angle of attack, oscillation amplitude and reduced frequency. Copyright  2010 John Wiley & Sons, Ltd. Received 23 July 2009; Revised 16 February 2010; Accepted 17 February 2010 KEY WORDS: stall; oscillatory airfoil; flow patterns; linear and nonlinear k –ε models; overset grids 1. INTRODUCTION Unsteady aerodynamic phenomena occur in modern fluid dynamic such as helicopters, Micro air vehicles (MIVs), turbines and turbo-machines and so on. Experiments show that time-dependent dynamic forces of helicopters’ rotor blades, plane blades, wind turbines and high-performance airplanes are greater than static forces in different conditions. The theory of unsteady aerodynamics for oscillatory airfoils was first focused on as an efficient solution to solve the Flutter problem. This theory was then used widely in biofluid dynamic since the forward movement of birds, insects and fish is justifiable using this theory. Earlier studies of oscillatory airfoils were conducted by Glauert [1]. However, a more detailed analysis of the issue was carried out by Theodorsen and Garrick [2] and is the basis for many aerodynamic analyses with the assumption of incompressible inviscid flow and low oscillation amplitude. Although successful efforts have been made to determine stagnant aerodynamic coef- ficients in steady flow in engineering sections by using numerical and empirical methods, there is still much to do in unsteady aerodynamics and determining aerodynamic coefficients in this condi- tion. Some experimental studies in this field include Breton et al.’s [3] in 1997 who worked on ∗ Correspondence to: M. J. Vafaei Rostami, Mechanical Engineering Department, Isfahan University of Technology, Isfahan, Iran. † E-mail: mjvafaeirostami@yahoo.com ‡ Assistant Professor. Copyright  2010 John Wiley & Sons, Ltd.