For several years, Airbus has been working with the ONERA in a project called RAPRO aiming to study the in uence that a boundary layer created by an axisymmetric body placed upstream has in the global performances of an engine ingesting this boundary layer. The existing numerical simulations, made during RAPRO's project, shown a decrease of power requirements for a given con guration but this simulations o er no access to the aerodynamic e ects occurring on the engine. The present work presents a numerical study of the aerodynamics of RAPRO's boundary layer ingesting system (BLI). The study will be mostly focused on the setup of a novel CFD model and also on the fan's performances when it encounters a non-uniform ow, with the existence of a boundary layer, created by an object placed upstream.