Methods are developed for calculation of mean velocity and pressure and mean turbulent kinetic energy, Reynolds tension, dissipation, etc. in turbulent incompressible flow after separation at a sudden increase in the cross-section of a circular duct. One method, based on the concept of effective turbulent viscosity and elliptical equations (because of the recirculation taking place), has allowed prediction of flow conditions from the point of separation to that a long way downstream at which normal flow is restored. Another method is associated more especially with the area in which normal flow is restored after readhesion; as the governing equations in this zone are parabolic, it has been possible to apply models containing Reynolds stress transport equations without the turbulent viscosity concept. The overall calculated data are compared with experimental results determined on an aerodynamics model used to study the effect of the initial boundary layer, Reynolds number and the cross-sectional expansion factor, and with other authors' data.