This paper summarizes the investigations performed to evaluate the interference of the wind tunnel walls on the intake flow of a UAV configuration within the framework of Garteur Action Group AG46. Experimental data gathered during a wind tunnel test campaign of the Eikon model-a high-transonic UAV prototype featuring a W-lip, S-shaped intake duct-performed by the Swedish Defence Research Agency (FOI) at the T1500 wind tunnel have been compared to CFD calculations simulating the Eikon model within the T1500 wind tunnel. Numerical results have been compared with experimental data in terms of pressure distribution on the model surface and flow field on the engine-intake Aerodynamic Interface Plane. Additionally, numerical calculations simulating the model both within a closed wind tunnel test section and in free-flight conditions have been performed. Interference of closed and ventilated wind tunnel walls has been evaluated by comparing numerical results in free-flight and within the wind tunnel test section with slotted and closed walls.