Enhancement of Engine Onow Conditions Using Vortex Generators within Curved Intake Channels

Abstract

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. Especially radar signature is the reason why submerged air intakes are preferred solutions, in fact backscattering is lowered. From the aerodynamic point of view partially submerging of air intakes can lead to short S-shaped ram air intake channels due to a limited integration space for engines and auxiliary systems. The benefit is a further reduction of radar signature, unfortunately, 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 total pressure can be observed at the aerodynamic interface plane (AIP), the engine throat plane. Beside Dean-like vortices additional flow separation inside the S-duct might occur. These effects are enforced at transonic flow conditions, in particular shocks are changing the boundary layer thickness in front of the intake. Moreover, maneuvers can lead to the occurrence of additional leading edge vortices or to a strong displacement of existing vortices. All those can lead to a dramatically changed air intake in flow situation, under which flow separation in the S-duct change the pressure distribution at the engine throat plane in a way that the homogeneity will decrease the performance of the engine.