The flow field around a two-dimensional slightly modified NACA 64 3 - 618 airfoil was investigated for two chord Reynolds numbers, Re = 64, 200 and Re = 137, 000. Surface- pressure distributions and total aerodynamic forces were measured for angles of attack in the range of -12° to 20°. Experimental results were compared to numerical results obtained by Direct Numerical Simulations and calculations using the two-dimensional design code XFOIL. Additionally, acoustic measurements and flow-visualizations were performed to study the transition and the separation behavior of the flow for various angles of attack. For certain angles of attack, separation bubbles developed which had a strong influence the airfoil performance. Using the combined approach, experimental and numerical, a deeper insight into the underlying physical mechanisms and into the separation and transition behavior of the boundary layer around the airfoil was obtained. Based on these results, passive and active flow-control strategies were investigated. The flow-control strategies aimed at improving the overall airfoil performance by preventing or at least reducing regions of separated flow.