The design constraints for air intakes of unmanned combat aerial vehicles (UCAVs) or manned combat aircrafts have been tightened and partially changed over the last decade. New requirements in regard to infrared and radar signature have a crucial impact on the aerodynamic shape of air intakes and their integration in the aircraft system. Radar signature is the main reason why submerged air intakes are preferred solutions, because backscattering is lowered. Partially submerging of air intakes together with a limited integration space for engines and auxiliary systems leads to short S-shaped ram air intake channels. The benefit is a further reduction of radar signature, however, from an aerodynamic point of view, a short S-shape of the intake channel has a severe impact on the onflow conditions for the engine. A strong inhomogeneity in regard to vortices and related concentrated total pressure losses can be observed at the aerodynamic interface plane (AIP), commonly the engine throat plane. Beside generated Dean-like vortices at curved sections of the intake channel additional flow separation inside the S-duct might occur. These effects are enforced at transonic flow conditions, in particular, where shocks are changing the boundary layer thickness in front of the intake. Moreover, maneuvers can lead to the occurrence of additional separating leading edge vortices or to a strong displacement of existing vortices. Each of those flow phenomena can lead to a dramatically changed air intake inflow situation and a S-duct flow. Eventually this changes the total pressure distribution at the engine throat plane in a way that a loss of homogeneity decreases the performance of the engine significantly. Thus, special attention has been laid on the aerodynamic design of the air intake and the S-duct. At that point flow control methods come into play: Focal point of the present work is the ability to reduce the observed inhomogeneity of total pressure loss distribution at the aerodynamic interface plane using vortex generators. More precisely, in this study vortex generator pairs are used to counteract the Dean vortices which are developing due to curvature of the S-shaped intake channel. Furthermore, single vortex generator configurations are investigated testing to cancel out the effect of separating vortices at asymmetric air intake onflow conditions. This CFD study concentrates on a generic partially submerged scoop like air intake combined with a quite short S-duct configuration which is typical for common unmanned aircraft systems. In this work we are comparing the experimental wind tunnel data with the numerical simulation results for this special configuration. For a certain reference onflow Mach number, a fixed mass flow rate and Reynolds number the flow structures of the uncontrolled and flow controlled cases at and within the partially submerged air intake are numerically examined and compared. Flow separation leading to the vortical flow structure is focal point of the analysis of the numerical simulation data. Their potential impact on the flow field at the AIP is part of our consideration, thus calculated DC(60), distortion values and total pressure loss information at a virtual engine throat plane are used for the evaluation of the flow control approach, their appropriateness is discussed.
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