An assessment on the unsteady flow distortion generated by an S-duct intake

Abstract

Closer integration between the fuselage and the propulsion system is expected for future aircraft to reduce fuel consumption, emissions, weight and drag. The use of embedded or partially embedded propulsion systems may require the use of complex intakes. However, this can result in unsteady flow distortion which can adversely affect the propulsion system efficiency and stability. This works assesses the characteristics of the unsteady flow with a view to the potential flow distortion presented to the compression system. Particle image velocimetry is used to measure the flow distortion generated by an S-shaped intake. The timeresolved tracking of the idealized relative incidence angle revealed that most frequent distortion events exhibited 90° exposure sector and up to ±5° mean relative incidence. The imposition of a thicker boundary at the S-duct inlet increased the probability of distortion events that are characterized by a longer exposure sector and higher relative incidence angles. Because of these characteristics, the distortion caused by the S-duct intake could induce instabilities that are detrimental for the propulsion system performances and stability. Overall, this work proposes a new method to assess the possible relative incidence angle on the compressor rotor taking into account the intake flow unsteadiness.

Aerodynamic Instabilities in High-Speed Air Intakes and Their Role in Propulsion System Integration

“…Studies revealed that flow distortion is associated with the boundary layer thickness. A thicker incoming boundary layer generates high levels of total pressure distortion [229] and swirl distortion, as it can generate early separation, leading to the growth of the contra-rotating vortices at the AIP [230]. Along with the thickness of the boundary layer, the orientation also plays a role; depending on the boundary layer orientation, compatibility issues may arise between the intake and the compressor [230].…”

“…A thicker incoming boundary layer generates high levels of total pressure distortion [229] and swirl distortion, as it can generate early separation, leading to the growth of the contra-rotating vortices at the AIP [230]. Along with the thickness of the boundary layer, the orientation also plays a role; depending on the boundary layer orientation, compatibility issues may arise between the intake and the compressor [230]. An asymmetric boundary layer can significantly change the spatial distributions of the lateral swirl switching mode and the vertical oscillatory mode of the bulk swirl [23].…”