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Current combat Unmanned Aerial Vehicles (UAVs) are being designed for a new threat environment demanding low observability and stealth capabilities, as well as for weight requirements. These aircraft are designed to minimize the overall radar cross section presented to enemy radar installations. Nevertheless, the desire to hide the engine face from direct observation leads to duct curvature and convolution and generates flow characteristics which can adversely affect engine performance. Moreover, line-of-sight obscuration over a short duct length increases the risk of flow separations within the duct at flight conditions. Consequently, enhanced understanding of the flow physics involved in complex innovative inlet design can result in improved methodologies for controlling these internal flows. In order to reduce costly wind tunnel experiments during the development phase of aerial vehicles, the ability to accurately predict the aerodynamic performance of highly integrated intakes is of great importance. This paper describes DES (Detached Eddy Simulation) computations performed for a subsonic UAV configuration within the Aerodynamics Action Group AD/AG-46 "Highly Integrated Subsonic Air Intakes" of the Group for Aeronautical Research and Technology in EURope (GARTEUR). The paper compares numerical results of hybrid RANS/LES (Reynolds-Averaged Navier-Stokes/Large Eddy Simulation) computations with steady RANS and unsteady RANS (URANS) data as well as with experimental data for the EIKON UAV configuration designed and tested at FOI in Sweden. The time evolutions of radial and circumferential distortion coefficients at the Aerodynamic Interface Plane (AIP) very well demonstrate the highly turbulent character of the flow in the separated region downstream of the S-duct. NomenclatureAIP = Aerodynamic Interface Plane, model scale D=0.1524m AAEM = ALENIA AERMACCHI AoA, α = Angle of Attack AoS, β = Angle of Sideslip CDI = Circumferential distortion descriptor CFD = Computational Fluid Dynamics Cp = Pressure coefficient (Cp = (p-p ∞ )/q ∞ ) D = Engine fan (AIP) diameter DC60 = Circumferential distortion based on 60-sectors at the AIP plane: DDES = Delayed Detached Eddy Simulation L = Total duct length, full scale=1.65m, model scale=0.38m M, Ma, m, mach = Mach number p = Static pressure P0 = Total pressure PR = Total pressure recovery at AIP q = Dynamic pressure RDI = Radial distortion descriptor Re = Reynolds number S-A, SA = Spalart-Allmaras (turbulence model) T = Static temperature x, y, z = Coordinates in reference coordinate system ZDES = Zonal Detached Eddy Simulation Δt = Time step size μ = Absolute (dynamic) viscosity, 1.7894·10 -5 N.S.m -2 , ISA at sea level Subscript: ∞ = Freestream (tunnel) conditions AIP = Average conditions at AIP ref = Calculated reference values t, tot = Total state

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