Separation and Transition Control via Active Flow Control: For flight vehicles, successful active flow control (AFC) strategies to mitigate the detrimental effects of boundary-layer separation for lifting surfaces could lead to significant performance gains. This is especially true for unmanned aerial vehicles (UAVs) which, due to the usually small wing dimensions and low air speeds, often operate within a Reynolds-number flight regime, for which a strong interaction exists between separation and transition. Using high-fidelity direct numerical simulations for a wing section with a modified NACA 643 − 618 airfoil at a chord Reynolds number of Re=200,000, it was shown that an AFC strategy using two-dimensional harmonic blowing and suction at a frequency commensurate with the shear layer instability of the separation bubble can significantly reduce the separation region. A surprising finding was that with forcing with properly chosen frequency and amplitude, transition is significantly delayed on the suction side and the flow remains virtually 2-D and laminar. The fact that for the controlled case the flow remains laminar far downstream suggests that the 2-D forcing with a large enough amplitude is suppressing the temporally growing 3-D disturbances because the secondary absolute instability is prevented. Contributors: Shirzad Hosseinverdi & Hermann F. Fasel