Multi-objective optimisation of short nacelles for high bypass ratio engines

Abstract

Future turbo-fan engines are expected to operate at low specic thrust with high bypass ratios to improve propulsive eciency. Typically, this can result in an increase in fan diameter and nacelle size with the associated drag and weight penalties. Therefore, relative to current designs, there is a need to develop more compact, shorter nacelles to reduce drag and weight. These designs are inherently more challenging and a system is required to explore and dene the viable design space. Due to the range of operating conditions, nacelle aerodynamic design poses a signicant challenge. This work presents a multi-objective optimisation approach using an evolutionary genetic algorithm for the design of new aero-engine nacelles. The novel framework includes a set of geometry denitions using Class Shape Transformations, automated aerodynamic simulation and analysis, a genetic algorithm, evaluations at various nacelle operating conditions and the inclusion of additional aerodynamic constraints. This framework has been applied to investigate the design space of nacelles for high bypass ratio aero-engines. The multi-objective optimisation was successfully demonstrated for the new nacelle design challenge and the overall system was shown to enable the identication of the viable nacelle design space.

Effects of Aircraft Integration on Compact Nacelle Aerodynamics

“…It is imperative to develop new methods for the design of compact congurations aimed at the reduction of the overall nacelle drag [5]. Nacelle aerodynamic design presents a notable challenge due to the dierent ow conditions that arise throughout the aircraft mission.…”

“…Nacelle architectures have been traditionally designed as a set of axisymmetric aero-lines, that in combination with droop and scarf form a 3D conguration. Tejero et al [5] developed a nacelle optimisation framework based on a CFD in-the-loop approach for compact axisymmetric aero-engines in which the sensitivity to the pertinent nacelle design parameters of L nac /r hi and r te /r hi was quantied. The limits of the feasible design space for this new nacelle design challenge were identied and design guidelines derived.…”

“…This work further develops the method developed by Tejero et al [5,20,21] for the aerodynamic analysis of isolated compact nacelle congurations. It designs, evaluates and optimises the geometry of a nacelle aero-engine for a set of user-prescribed ight conditions and geometric and aerodynamic constraints [5].…”

“…This work further develops the method developed by Tejero et al [5,20,21] for the aerodynamic analysis of isolated compact nacelle congurations. It designs, evaluates and optimises the geometry of a nacelle aero-engine for a set of user-prescribed ight conditions and geometric and aerodynamic constraints [5]. The framework incorporates a series of modules for the geometry denition [22,23], a mesh generation tool [24], compressible ow solution [25], extraction of the nacelle performance metrics using AGARD industrial standards [26] and a multi-point multi-objective optimisation capability coupled with a genetic algorithm [27].…”

“…For these new architectures, the nacelle length (L nac ) and maximum radius (r max ) will be reduced as much as possible to minimise the fancowl wetted area and, as such, the cowl drag force. Nevertheless, this new nacelle design style may present lower curvature and a concomitant wave drag penalty at transonic con-ditions [5]. Consequently, it is imperative to identify the feasible design space for the new nacelle design challenge.…”