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 achallenge for Computational Fluid Dynamics (CFD). The main goal of this work wasa computational study of the effects of boundary-layer forcing on the mean flow andturbulence 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 incomplex flow situations. Predictive capability of various CFD methods were evaluatedfor the three representative complex separated flow configurations without flowcontrol. A potential of the methods for unsteady flow computations: LES, DESand URANS was investigated by predicting the flow and turbulence field for thetwo experimentally investigated AFC configurations. The numerous simulations of the flow configurationspertinent to active flow control (AFC) have been carried out providinga picture of the current status of CFD in AFC applications.