In the present work, a computational fluid dynamics (CFD) model was developed to describe both of the extreme regimes (viscous and turbulent), including the transition regime. The second objective was to examine the extent to which CFD models are able to describe quantitatively the variation of epsilon(G) with V-G as a function of flow regimes. This study helps to underline the distinguishing characteristics of both regimes: homogeneous and heterogeneous. An extensive comparison of predicted mean axial liquid velocity profiles and fractional gas hold-up profiles with the experimental data has been presented. The agreement has been shown to be excellent. The CFD model has also been compared with the simplified analytical solutions. In a fully developed heterogeneous regime and under turbulent conditions, the reversal point for the axial velocity was found to be in the range of 0.7-0.75R. With a decrease in the Reynolds number (DVCrhoL/mu(L)), the reversal point was found to shift toward the center up to 0.5R. Further, the CFD simulation was found to reveal a large number of characteristic features of flow in viscous and transition regimes.