Numerical Flow Field Analysis in a Highly Bent Intake Duct

Abstract

In many modern aircraft concepts, civil as well as military ones, the engine is fully integrated into the fuselage. This integration often requires a highly bent intake duct. Due to the high degree of curvature and also the diffusive character of the intake duct, the inflow at the engine’s fan is non-uniform and may feature severe flow distortions. The size, strength, and pattern of these flow distortions may affect the engine’s compressor system and its safety margins. In this paper the flow through a short highly bent intake duct geometry is analysed by means of CFD. The numerical simulations are validated against experimental data, which are obtained in extensive investigations at the institute’s engine test facility. The setup for the numerical investigations is based on previous studies of the aerodynamics of intake ducts at the Institute of Jet Propulsion, where it is shown that the shape of the entrance cross-section of the intake duct has a strong influence on the flow field throughout the entire intake duct. In this paper the flow throughout the duct is analysed in order to gain information on the flow features which cause the flow distortion at the aerodynamic interface plane (AIP) and how these flow features interact. Two main flow distortion patterns exist at the AIP, one of them is a system of two twin vortices, one on each side in the lower part of the AIP. These are caused by the particular shapes of the cross-sections in the front part of the duct. The dominating flow distortion in the AIP is caused by a large flow separation in the rear part of the duct, which resides in the upper half of the AIP and results in a large total pressure loss and axial velocity deficit, combined with a twin swirl. Although no direct interaction between these two flow patterns is present, it was found that the small vortices in the lower part are influenced by the flow separation at the upper wall in the rear section of the intake duct.