The maximum lift coefficient that can be obtained with a certain airfoil is limited by the onset of ow separation. At a certain angle of attack the adverse pressure gradient becomes so strong that the ow can no longer follow the surface of the airfoil and separates, resulting in a decrease in lift and an increase in drag. This maximum lift coefficient can be increased by using high-lift devices like trailing edge aps. However, ow separation still remains the limiting factor. Flow separation control is a solution to this problem. By adding momentum to the boundary layer ow separation is postponed and higher lift coefficients can be reached. In this research active ow separation control by means of a vibrating surface element, a so-called fliperon, is investigated. Both the effectiveness and the efficiency of this flow control method are investigated for the NACA-0015 airfoil at 20 angle of attack and for the NLR7301 airfoil-flap configuration with ow separation from the 35 deflected flap. This research is performed completely numerically with the ow solver Fluent 6. For this research the RANS equations are closed with the k-E turbulence model. Because the fliperon is oscillating during the simulation, the dynamic mesh model is used to rotate the fliperon and to keep the grid quality at a sufficient level. The fliperon was located at a distance of about 20% (flap) chord length ahead of the ow separation point. The length is chosen such that the maximum amplitude of the fliperon tip equals the local boundary layer thickness. Further the shape of the fliperon is equal to the curvature of the airfoil at that location. If the fliperon oscillates above a cavity, the shape of the cavity will also influence the generated vortices. The best results were obtained with a round cavity shape that increases the blowing effect in tangential direction and reduces the amount of additional vorticity that is generated. The performances of a fliperon oscillating above a cavity with a sharp trailing edge and a springboard type fliperon were less promising. The most important parameter of the fliperon motion is the frequency. The frequency influences the size and the strength of the generated vortices. It is important that the generated vortices are sufficiently strong, because they have to travel towards the trailing edge and interact with the vortices that existed there due to the ow separation. Only then the total circulation is improved and the lift coefficient increased. In case of the NACA-0015 a dimensionless frequency F+ of 1.2 turned out to be very effective, while the most effective frequency on the NLR7301 airfoil-flap configuration was 6.0. The fliperon motion should be defined such that the maximum amplitude of the fliperon tip is equal to the boundary layer thickness. Larger amplitudes did not lead to an additional improvement of the lift coefficient, while too small amplitudes did not improve the lift coefficient at all. On the NACA-0015 airfoil the maximum increase in lift coefficient obtained by the application of a fliperon was 20% with respect to the uncontrolled situation. The corresponding momentum coefficient was 0.016, which makes the fliperon both an effective and an efficient method of ow control in this case. On the NLR7301 airfoil flap configuration the maximum increase in lift coefficient was 21.2%, with a corresponding momentum coefficient of 0.144. Although the fliperon is still effective in this case, the momentum is now used less efficiently compared to other types of active ow control. Here the advantage of the fliperon is that it is less complex than several other ow control methods. There are many ways in which the current research can be continued. In future numerical research it would be interesting to perform a large eddy simulation to investigate the influence of the cavity shape on the produced vortices in more detail. Further it is recommended to investigate the effect of different fliperon motions. Since the current research has shown the effectiveness of the fliperon as ow control device, the risk of a wind tunnel experiment is reduced. In such an experiment the simulations can be validated, and the optimal frequency and amplitude ratio can be determined more accurately. Also the influence of 3D effects can be investigated. Furthermore the efficiency of the fliperon can be determined more accurately by measuring the required power.