Abstract: To explore the effect of surface pollution on the aerodynamics of airfoils, the aerodynamic performance of DU airfoils and NACA44XX airfoils with different thicknesses is numerically simulated using the SST k-ω model. The sensitive positions of fixed transition for two series airfoils are examined, and the variations in aerodynamic performance, stall and internal flow features are analyzed. The results show that the sensitive position of fixed transition is closely related to airfoil shapes, but the aerodynamic performance is almost independent of the thickness of airfoils. For DU and NACA44XX airfoils, the sensitive positions of fixed transition are located at 1%c on the suction surface and 5%c and 9%c on the pressure surface, respectively. The influence of the fixed transition on aerodynamics is more prominent for airfoils with large thicknesses, and the airfoils with large thicknesses are more sensitive to variation in fixed transition position. The impact of fixed transition on the aerodynamics of NACA44XX airfoils is more notable than that of DU airfoils and is more significant with increasing airfoil thickness. The increase in relative thickness leads to a larger size of the high vortex region and the overall vortex mass near the fixed transition position. The main reason for the effect of relative thickness and shape on the sensitivity of fixed transition is mainly characterized by the separation of vortices at the trailing edge.