This paper is concerned with the design and performance of an annular S-shaped duct that would be used to connect an LP fan to the core within a gas turbine engine. The desire to minimise engine length means the duct is of relatively short length so that, without novel design, flow separation is likely to occur. Hence the upstream OGV row has been leant tangentially so that it assists in turning the flow within the first bend of the S-shaped duct. In such an ‘integrated’ design, a component of the lift force generated by the OGV row turns the flow radially inward. In this way, the aerodynamic loading on the critical inner wall boundary layer, within the downstream S-shaped duct, is reduced. In addition, by incorporating the blade row within the duct, rather than upstream of it, a further length reduction can also be achieved. The paper outlines the OGV design methodology and presents experimental results that define the aerodynamic performance of the integrated system. The overall system loss is determined mainly by the OGV row, and the subsequent mixing out of the blade wakes prior to the inlet of the core duct. In addition, for the range of conditions tested, the stagnation pressure profile at core duct exit reflects that portion of the OGV exit profile that is captured by the core duct.
An investigation was carried out into the effects of variable inlet guide vanes (VIGVs) on the performance and stability margin of a transonic fan in the presence of inlet flow distortion. The study was carried out using computational fluid dynamics (CFD) and validated with experimental data. The capability of CFD to predict the changes in performance with or without VIGVs in the presence of an inlet flow distortion is assessed. Results show that the VIGVs improve the performance and stability margin and do so by reducing the amount of swirl at inlet to the rotor component of the fan.
Strong aerodynamic coupling can make the high fidelity simulation of a number of critical aero-engine components prohibitively expensive — particularly within the timeframes of industrial design cycles. This paper develops a body force based hierarchy of approaches to modelling the effects of blade rows. These are envisaged as allowing the computationally expensive parts of coupled systems to be resolved much more cheaply, rendering the cost of the overall simulation as more manageable. Simulation of the coupling that exists between the flow around an aero-engine intake and its fan is particularly emphasised, as this is becoming stronger and more performance critical with the modern trends towards the reduction of the relative diffuser length. The use of the viscous smeared geometry level of fidelity is initially shown to be an effective model over a number of cases — a simple compressor blade row, a modern high bypass fan, and the Darmstadt rotor. After this, it is shown working as part of a coupled system in an intake experiencing cross-flow. Higher fidelity geometry representations are then considered, which mimic the effect of struts. Finally, a mix of various fidelity geometry representations and turbulence modelling approaches is shown to bring otherwise hugely expensive calculations within the realm of practical computation, in the form of a full fan-to-flap calculation.
The effect of inlet distortion from curved intake ducts on jet engine fan stability is an important consideration for next-generation passenger aircraft such as the boundary layer ingestion (BLI) “silent aircraft.” Highly complex inlet flows which occur can significantly affect fan stability. Future aircraft designs are likely to feature more severe inlet distortion, pressing the need to understand the important factors influencing design. This paper presents the findings from a large computational fluid dynamics (CFD) investigation into which aspects of inlet distortion cause the most significant reductions in stall margin and, therefore, which flow patterns should be targeted by mitigating technology. The study considers the following aspects of distortion commonly observed in intakes: steady vortical distortion due to secondary flow, unsteady vortical distortion due to vortex shedding and mixing, static pressure distortion due to curved streamlines, and low momentum endwall flow due to thickened boundary layers or separation. Unsteady CFD was used to determine the stall points of a multipassage transonic rotor geometry with each of the inlet distortion patterns applied. Interesting new evidence is provided, which suggests that low momentum flow in the tip region, rather than distortion in the main body of the flow, leads to damaging instability.
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