Abstract
Abstract As the growth of aviation continues it is necessary to minimise the impact on the environment, through reducing NOx emissions, fuel-burn and noise. In order to achieve these goals, the next generation of Ultra-High Bypass Ratio engines are expected to increase propulsive efficiency through operating at reduced specific thrust. Consequently, there is an expected increase in fan diameter and the associated potential penalties of nacelle drag and weight. In order to ensure that these penalties do not negate the benefits obtained from the new engine cycles, it is envisaged that future civil aero-engines will be mounted in compact nacelles. While nacelle design has traditionally been tackled by multi-objective optimisation at different flight conditions within the cruise segment, it is anticipated that compact configurations will present larger sensitivity to off-design conditions. Therefore, a design method that considers the different operating conditions that are met within the full flight envelope is required for the new nacelle design challenge. The method is employed to carry out multi-point multi-objective optimisation of axisymmetric aero-lines at different transonic and subsonic operating conditions. It considers mid-cruise conditions, end-of-cruise conditions, the sensitivity to changes in flight Mach number, windmilling conditions with a cruise engine-out case and an engine-out diversion scenario. Optimisation routines were conducted for a conventional nacelle and a future aero-engine architecture, upon which the aerodynamic trade-offs between the different flight conditions are discussed. Subsequently, the tool has been employed to identify the viable nacelle design space for future compact civil aero-engines for a range of nacelle lengths.
Highlights
There is a clear need to reduce fuel-burn, perceived noise and NOx emissions to reduce the environmental impact of aviation, while simultaneously responding to societal needs [1]
The method has been employed to carry out several multi-objective optimisations, in which different flight conditions that are met throughout the flight envelope were considered
Whilst nacelle design has been traditionally tackled by considering conditions within the cruise segment, the proposed method evaluates different windmilling scenarios to ensure the robustness of the nacelle aerodynamic design
Summary
There is a clear need to reduce fuel-burn, perceived noise and NOx emissions to reduce the environmental impact of aviation, while simultaneously responding to societal needs [1] In this respect, it is expected that future civil aero-engines will operate at high bypass ratios (BPR) and low fan pressure ratios (FPR) [2] to increase the propulsive efficiency through operating at reduced specific thrust. The nacelle length (Lnac) may be shortened as much as possible to reduce the overall wetted area and nacelle drag. This will result in a fancowl curvature reduction and a wave drag penalty [4]. For these new, challenging nacelle designs it is imperative to identify the feasible design space that does not compromise the benefits from the new engine cycles
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