Aqueous foam is a non-Newtonian complex fluid. Its flow through the singularities presents many fundamental aspects. The rheological character of the foams flowing in this kind of geometries can create important disturbance on its behavior, according to the flow rate set and therefore a modification in its texture and in the nature of its established regime. During this study, numerical simulation for the case of a half-sudden expansion was developed using the Herschel-Bulkley rheological model. The model is used to describe the response of foams during under flowing conditions through this type of singularity. Obtained CFD results are focused on the pressure losses, velocity fields of the foam flow in various positions of the channel using different qualities (variation of void fraction) for lower velocities’ case (one-dimensional regime) and for the three-dimensional regime. Firstly, we validated the use of this type of non-Newtonian foam flow fluid to describe the flow reorganization through a half-sudden. In a second step, we used an experimental database to validate our CFD pressure losses and velocity fields. The comparison of these results with those obtained experimentally by Chovet shows a good agreement for lower speed foam flow, but with some uncertainty for higher foam flow velocities.