The transient simulation of large scale bubbly flow in bubble columns using the unsteady Reynolds averaged Navier Stokes (URANS) equations is investigated in the present paper. An extensive set of bubble forces is used with different models for the bubble induced turbulence. Criteria are given to assess the independence of the simulation time and the time step length. Using these criteria it is shown that a simulation Lime, time step length and mesh independent solution can be obtained for complex bubbly flows using URANS equations under certain requirements. With the obtained setup the contribution of the resolved turbulence to the total turbulence and the influence of the bubble induced turbulence modeling on the resolved turbulence is investigated. Further, it is pointed out that the virtual mass force is not negligible. The simulations arc compared to data from the literature at two different superficial velocities, which cover monodisperse and polydisperse bubbly flows. (C) 2014 Elsevier Ltd. All rights reserved.