In this thesis, a submerged inlet type for the engine core of the boundary layer ingesting APPU (Advanced Propulsion and Power Unit) is designed. The aim is to evaluate key geometric parameters that impact the flow field at the intake region by computing 3D CFD simulations. Various designs are created where entrance thickness, corner radius, duct shape, lip shape and entrance azimuthal range are altered. Assessment criteria include the distortion coefficient, drag coefficient and total pressure recovery. Additionally, wall shear stress, Mach and pressure contours are visualized to conduct comparisons between design iterations and identify (detrimental) flow phenomena. Results show that the total pressure recovery in all cases is below 80%, but losses confined to the interior of the duct can reach values lower than 1%. The findings of this thesis further elaborate on the significance of the various shape parameters and their impact on the flow field.