This paper presents an investigation on the effect of introducing large-scale roughness through static curvature modifications on the low speed flow over an airfoil. The surfaces of a standard NACA 4415 airfoil have been modified with regular perturbations or “bumps” of the order of 2%c for this purpose. While the actual NACA 4415 airfoil is not a suitable candidate for low Re cases due to extensive prevalence of boundary layer separation, it is expected that the bumps would exercise passive flow control by promoting early transition to turbulence, thereby reducing the extent of separation and improving the performance. From this investigation it has been found that the separation bubbles begin on the upper surface of the bumpy surface model is later than the regular surface model. This implies that the stall appears of bumpy surface model at higher attack angle than the regular surface model. The lift to drag ratio also increases for bumpy surface airfoil and consequently improve the performance of the wing. Experiments are conducted for chord based Re values ranging from 25,000 to 500,000