Recent experimental studies have demonstrated that active flow control (AFC) has a potential to enable significant advances in many engineering applications. Though demonstrated experimentally, unsteady separation flow control remains a challenge for Computational Fluid Dynamics (CFD). The main goal of this work was a computational study of the effects of boundary-layer forcing on the mean flow and turbulence using various methods for turbulent flow computations: Large-eddy simulation (LES), Reynolds-averaged Navier-Stokes (RANS) and Detached-eddy Simulation (DES), aiming also at mutual comparison of their features and performance in complex flow situations. Predictive capability of various CFD methods were evaluated for the three representative complex separated flow configurations without flow control. A potential of the methods for unsteady flow computations: LES, DES and URANS was investigated by predicting the flow and turbulence field for the two experimentally investigated AFC configurations. The numerous simulations of the flow configurations pertinent to active flow control (AFC) have been carried out providing a picture of the current status of CFD in AFC applications.