Vortex generators (VGs) are commonly-used effective flow separation control devices, and are proved to have potential to improve the aerodynamic performance of large wind turbines. In this paper, the flow physics of VGs and how their size affects the aerodynamic performance of a blunt trailing-edge airfoil DU97-W-300 have been investigated using CFD simulations. Based on wind turbine dedicated airfoil with and without VGs respectively, three-dimensional numerical models were established and further validated through the comparisons between the numerical results and the experimental data. The effects of VGs' size were analyzed from several perspectives, such as trailing-edge height, length, short and long spacing between an adjacent pair of VGs. The results indicate that drag penalty is more sensitive to the increase of VG height than lift; an increment of VG length leads to negative effects on both lift and drag; increases of the spacing between an adjacent pair of VGs have positive impact on suppression of separated flow. Additionally, the flow field characteristics were further revealed by the analysis of streamlines and vortices in the wake region. (C) 2014 Elsevier Ltd. All rights reserved.