Abstract
Abstract To reduce fuel-burn and emissions, there is a drive toward higher bypass ratio and smaller high-pressure ratio core engines. This makes the design of the ducts connecting compressor spools more challenging as the higher radius change increases aerodynamic loading. This is exacerbated at inlet to the engine core by fan root flow which is characterized by a hub-low-pressure profile and large secondary flow structures. Additionally, shorter, lighter nacelles mean that the intake may not provide a uniform inlet flow when the aircraft is at an angle of attack or subject to cross winds. Such inlet distortion can further degrade the flow entering the engine. A combination of experiments and computational fluid dynamics (CFD) has been used to examine the effects on the aerodynamics of an engine section splitter (ESS) and transition duct designed to feed the low-pressure spool of a high bypass ratio turbofan. A test facility incorporating a 1½ stage axial compressor was used to compare system performance for a flat rotor exit profile to one with a hub deficient flow. Validated Reynolds averaged Navier–Stokes (RANS) CFD was then used to further investigate the effects of increased inlet boundary layer thickness and bulk swirl distortion at rotor inlet. These changes were seen to have a surprisingly small effect on the flow at the duct exit. However, increased secondary flows were observed which degraded the performance of the ESS and significantly increased loss. Nevertheless, the enhanced mixing delayed separation in the duct suggesting that overall the design was reasonably robust albeit with increased system loss.
Highlights
In a multi‐spool compression system, the diameter of each spool reduces as the air density increases
To assess the effect of an increased hub boundary layer the profile shown in Fig. 17 was applied to the CFD inlet upstream of the Phase 2 rotor
Radial equilibrium dictates that the pressure profiles will be adjusted by the CFD, but this is a secondary effect in comparison to the increased momentum deficit for the first 40% of the span
Summary
In a multi‐spool compression system, the diameter of each spool reduces as the air density increases. The annular transition ducts connecting spools generally take the form of an S‐shape. The curvature in these ducts makes them prone to flow separation which must be avoided as it will compromise performance. There has been large amount of work studying the complex flow in annular S‐shaped ducts which develops under the combined influence of pressure gradients and streamline curvature. Ortiz‐Duenas et al [8], Barker et al [9,10], Karakasis et al [11], and Walker et al [12,13,14] studied more aggressive ducts and improved integration with the compression system
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