A two dimensional mathematical model DUCT, which is based on a parabolic boundary layer technique, using finite elements, is proposed to predict the flow and turbulence field in complicated geometrical conditions, where recirculating flow may occur. Numerical results of the DUCT-model are compared with k-eps-predictions as well as laboratory experiments concerning the flow in a number of configurations. In the case of a steep lee-side the location of the separation point is not well located, because the normal stresses in the equation of motion are neglected. Generally the velocities in the deceleration and acceleration zone are satisfactory. An advantage of the application of the DUCT-model compared with the sophisticated k-E-model is the relatively low computation time used to solve the set of equations.