Different wall-bounded flow configurations featured by the boundary layer separation are investigated computationally by using LES (Large-Eddy Simulation), a two-layer, hybrid LES/RANS (HLR) and RANS (Reynolds-Averaged Navier Stokes) methods. The flow cases investigated are featured by a systematic increase in the wall complexity: a backward-facing step flow (Re H =5540; Exp., Kasagi and Matsunaga, 1995), flow in a plane diffuser (Re m =18000; Exp., Obi et al., 1993, Buice andEaton, 1997), periodic flow over an axisymmetric hill (Re H =10800; LES, Froehlich et al., 2005) and flow over a hump (Re C =936000; Exp., Greenblatt et al., 2004). The main objective of the present work is the in-depth analysis of the flow structure aiming at establishing appropriate criteria for the flow unsteadiness characterization, marking the RANS method capabilities with respect to capturing correctly the mean flow characteristics relative to the LES-related methods.