Influence of Cross-Sectional Shape on the Flow in a Highly Bent Research Intake Duct for Jet Engines

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 five highly bent intake duct geometries are analyzed by means of CFD. They evolve from the same baseline geometry but are defined by different crosssectional shapes. With this variation of the cross-sections, the influence of the cross-sectional shape on the aerodynamics of the intake duct is investigated qualitatively. Based on these analyses a sixth intake duct geometry was created as test vehicle for experimental investigation of intake-compressor interaction within the engine test facility. The defining cross-sectional shapes were selected in order to achieve a flow distortion at the duct outlet plane, that is small enough to ensure a safe engine operation, but is still strong enough to provoke interaction of the distorted flow and the compressor flow. The setup for these fully numerical investigations is based on previous studies of the aerodynamics of intake ducts at the Institute of Jet Propulsion. It is shown that the entrance cross-section has a strong influence on the flow throughout the whole intake duct. Additionally, it could be determined that the flow distortion caused by the strong curvature of the intake duct can be reduced in size and strength by a proper combination of cross-sectional shapes.