An experimental procedure for investigating transient bubble flow for an adiabatic air/water system with vertical upward Row in a pipe is presented. The results of the measured local transient two-phase flow parameters are shown along a pipe length of approx. four meters. From the measured radial phase distributions under steady and under transient conditions one can draw conclusions about the interfacial forces. Here, the effects indicate the action of forces such as a transverse lift force and a time dependent force like the virtual mass force during the transient. For modelling the transverse lift force which seems to play a dominant role for that flow regime the formulation of Zun was chosen and it was implemented into the commercial CFD-Code Fluent Release 4.4.4 via user-defined subroutines. Finally, results from the simulation of the steady states of start and end conditions of an experimental measured transient are shown.