Design optimisation of separate-jet exhausts for the next generation of civil aero-engines

Abstract

The next generation of civil large aero-engines will employ greater bypass ratios compared with contemporary architectures. This results in higher exchange rates between exhaust performance and specific fuel consumption (SFC). Concurrently, the aerodynamic design of the exhaust is expected to play a key role in the success of future turbofans. This paper presents the development of a computational framework for the aerodynamic design of separate-jet exhaust systems for civil aero-engines. A mathematical approach is synthesised based on class-shape transformation (CST) functions for the parametric geometry definition of gas-turbine exhaust components such as annular ducts and nozzles. This geometry formulation is coupled with an automated viscous and compressible flow solution method and a cost-effective design space exploration (DSE) approach. The framework is deployed to optimise the performance of a separate-jet exhaust for very-high-bypass ratio (VHBR) turbofan engine. The optimisations carried out suggest the potential to increase the engine’s net propulsive force compared with a baseline architecture, through optimum exhaust re-design. The proposed method is able to identify and alleviate adverse flow-features that may deteriorate the aerodynamic behaviour of the exhaust system.

Impact of installation on a civil large turbofan exhaust system at idle descent conditions

“…The aerodynamic analysis for this study utilises the numerical framework developed for the design and analysis of separate-jet high and very high bypass ratio turbofan engines [10,42,12,43,44,26]. In particular, the current study follows the methodology reported by Goulos et al [26] for the design, meshing, CFD analysis, and performance evaluation of aero-engines [10,45,46].…”

“…The maximum variation from the őnal reported value was less than ±0.0005 of the mean value computed over the last 200 iterations. The CFD methodology used in this study has previously been used in the design analysis of HBR and VHBR aero-engines [26,38,44,12,61].…”

“…Another factor is the pylon blockage of the annular ducts, which is taken into consideration while sizing the nozzle throat and exit areas. In the preliminary stages of engine design, the design optimisation of the nozzle aero-lines is carried out with respect to these two metrics [12]. However, external ŕow suppression effects, engine-airframe interaction, incidence effects, together with the engine cycle conditions, such as the nozzle pressure ratios of the bypass and the core nozzle play a signiőcant role in determining the value of these performance metrics [13].…”

Coupled propulsive and aerodynamic analysis of an installed ultra-high bypass ratio powerplant at high-speed and high-lift conditions

“…2) to improve the alignment of the powerplant with the flow. Also, a separate exhaust design is included based on a multi-objective optimisation of the exhaust performance [22]. A bespoke pylon design is included in this configuration, and areas of the exhaust are corrected to compensate for the pylon blockage effects [8].…”

“…This requires the optimisation of the installed powerplant. However, this increases the computational cost in comparison with other approaches to optimise the housing components in isolation [21,22]. Thus, advanced design techniques such as multi-fidelity methods and dimensionality reduction [9] should be explored to enable the concurrent optimisation of the powerplant integration and the engine cycle.…”