Numerical simulation of a wind turbine airfoil: Dynamic stall and comparison with experiments

Abstract

Unsteady aerodynamic characteristics of the National Renewable Energy Laboratory S809 airfoil, undergoing sinusoidal pitch oscillations at various reduced frequencies, mean angles of attack, and pitch oscillation amplitudes at Re = 106, are investigated through solutions of two-dimensional Navier—Stokes equations. It is found that there is an encouraging agreement between the computational fluid dynamics (CFD)-predicted aerodynamic force coefficient hysteresis loops and the Ohio State University wind tunnel experimental data, although discrepancies still exist at higher angles of attack and during downstroke pitch motion. The effects of some parameters are studied, and the flow behaviour and dynamic stall vortex development of a typical case are represented in great detail by streamline distribution and pressure coefficient plots. CFD methodology is proved to be promising in predicting airfoil dynamic stall characteristics, and the impact of dynamic stall on the practical operation of wind turbines is analysed. It is necessary to take this into consideration in the prediction of wind turbine performance.