INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS Int. J. Numer. Meth. Fluids 2003; 42:163–186 (DOI: 10.1002/d.478) Computational study of unsteady turbulent ows around oscillating and ramping aerofoils G. N. Barakos ∗; † and D. Drikakis ‡ Engineering Department; Queen Mary; University of London; London E1 4NS; U.K. SUMMARY The aim of this work is to computationally investigate subsonic and transonic turbulent ows around oscillating and ramping aerofoils under dynamic-stall conditions. The investigation is based on a high- resolution Godunov-type method and several turbulence closures. The Navier–Stokes and turbulence transport equations are solved in a strongly coupled fashion via an implicit-unfactored scheme. We present results from several computations of ows around oscillating and ramping aerofoils at various conditions in order to (i) assess the accuracy of dierent turbulence models and (ii) contribute towards a better understanding of dynamic-stall ows. The results show that the employed non-linear eddy- viscosity model generally improves the accuracy of the computations compared to linear models, but at low incidence angles the Spalart–Allmaras one-equation model was found to provide adequate results. Further, the computations reveal strong similarities between laminar and high-Reynolds number dynamic- stall ows as well as between ramping and oscillating aerofoil cases. Investigation of the Mach number eects on dynamic-stall reveals a delay of the stall angle within a range of Mach numbers. Investigation of the reduced frequency eects suggests the existence of an (almost) linear variation between pitch rate and stall angle, with higher slope at lower pitch rates. The pitch rate aects both the onset of dynamic-stall as well as the evolution of the associated vortical structures. Copyright ? 2003 John Wiley & Sons, Ltd. 1. INTRODUCTION In the context of aerodynamics, the numerical simulation of unsteady, turbulent and compress- ible ows around moving boundaries is motivated by the need to understand ow phenom- ena associated with the behaviour of aircrafts during manoeuvres, as well as ows around helicopter rotors and turbomachinery blades. The ow phenomena appearing in the above ∗ Correspondence to: G.N. Barakos, CFD Laboratory, Department of Aerospace Engineering, University of Glasgow, Glasgow G12 8QQ, U.K. † E-mail: gbarakos@aero.gla.ac.uk ‡ E-mail: d.drikakis@qmw.ac.uk Contract=grant sponsor: EP-SRC=MoD; contract=grant number: GR=L18457 Contract=grant sponsor: Brite=EuRam project UNSI Contract=grant sponsor: European Union; contract=grant number: BRPR-CT97-0583 Received April 2001 Copyright ? 2003 John Wiley & Sons, Ltd. Revised 18 November 2002