Browsing by Author "MacManus, David"
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Item Open Access Aerodynamic design of separate-jet exhausts for future civil aero-engines, Part II: design space exploration, surrogate modeling, and optimization(American Society of Mechanical Engineers, 2016-03-15) Goulos, Ioannis; Otter, John; Stankowski, Tomaz; MacManus, David; Grech, Nicholas; Sheaf, ChristopherThe aerodynamic performance of the bypass exhaust system is key to the success of future civil turbofan engines. This is due to current design trends in civil aviation dictating continuous improvement in propulsive efficiency by reducing specific thrust and increasing bypass ratio (BPR). This paper aims to develop an integrated framework targeting the automatic design optimization of separate-jet exhaust systems for future aero-engine architectures. The core method of the proposed approach is based on a standalone exhaust design tool comprising modules for cycle analysis, geometry parameterization, mesh generation, and Reynolds-averaged Navier–Stokes (RANS) flow solution. A comprehensive optimization strategy has been structured comprising design space exploration (DSE), response surface modeling (RSM) algorithms, as well as state-of-the-art global/genetic optimization methods. The overall framework has been deployed to optimize the aerodynamic design of two civil aero-engines with separate-jet exhausts, representative of current and future engine architectures, respectively. A set of optimum exhaust designs have been obtained for each investigated engine and subsequently compared against their reciprocal baselines established using the current industry practice in terms of exhaust design. The obtained results indicate that the optimization could lead to designs with significant increase in net propulsive force, compared to their respective notional baselines. It is shown that the developed approach is implicitly able to identify and mitigate undesirable flow-features that may compromise the aerodynamic performance of the exhaust system. The proposed method enables the aerodynamic design of optimum separate-jet exhaust systems for a user-specified engine cycle, using only a limited set of standard nozzle design variables. Furthermore, it enables to quantify, correlate, and understand the aerodynamic behavior of any separate-jet exhaust system for any specified engine architecture. Hence, the overall framework constitutes an enabling technology toward the design of optimally configured exhaust systems, consequently leading to increased overall engine thrust and reduced specific fuel consumption (SFC).Item Open Access Aerodynamics of a short intake in crosswind(Elsevier, 2022-09-05) Boscagli, Luca; Christie, Robert; MacManus, David; Piovesan, TommasoThe next generation of turbofan aero-engines are likely to have an increase in fan diameter to reduce the specific thrust and increase the overall propulsive efficiency. More compact nacelles with possibly shorter intakes may be used to reduce weight and drag and achieve a net reduction of fuel consumption. For these compact nacelles a key consideration is the design of the short intake at the off-design conditions such as crosswind and high incidence operations. The close coupled interaction between a short intake and the fan at these off-design conditions is one of the key challenges. Previous work focused on the impact of short intake aerodynamics on the fan but there is a similar requirement to understand the impact of the fan on the viable short intake design space. This paper addresses the influence of the fan on the separation onset of the flow within a short intake under crosswind conditions. The effect of the fan on the separation characteristics of the intake boundary layer was considered both from a steady and an unsteady point of view. A hierarchy of fan computational models was used to separately assess the different aerodynamic contributions and to evaluate a net effect of the fan on the intake critical condition. Steady computational fluid dynamics analyses showed a notable positive effect of the fan on total pressure loss at post-separation conditions relative to a configuration without the fan. However, unsteady analyses revealed that fan unsteadiness has an adverse impact on the intake separation characteristics which reduces the intake critical conditions by about 15%. The main mechanisms behind the unsteady interaction were identified. Overall this work addresses, for the first time, the role of fan unsteadiness on the separation characteristics of the boundary layer within a short intake in crosswind.Item Open Access Artificial neural network for preliminary design and optimisation of civil aero-engine nacelles(Cambridge University Press, 2024-04-29) Tejero, Fernando; MacManus, David; Heidebrecht, Alexander; Sheaf, Christopher T.Within the context of preliminary aerodynamic design with low order models, the methods have to meet requirements for rapid evaluations, accuracy and sometimes large design space bounds. This can be further compounded by the need to use geometric and aerodynamic degrees of freedom to build generalised models with enough flexibility across the design space. For transonic applications, this can be challenging due to the non-linearity of these flow regimes. This paper presents a nacelle design method with an artificial neural network (ANN) for preliminary aerodynamic design. The ANN uses six intuitive nacelle geometric design variables and the two key aerodynamic properties of Mach number and massflow capture ratio. The method was initially validated with an independent dataset in which the prediction error for the nacelle drag was 2.9% across the bounds of the metamodel. The ANN was also used for multi-point, multi-objective optimisation studies. Relative to computationally expensive CFD-based optimisations, it is demonstrated that the surrogate-based approach with ANN identifies similar nacelle shapes and drag changes across a design space that covers conventional and future civil aero-engine nacelles. The proposed method is an enabling and fast approach for preliminary nacelle design studies.Item Open Access Characteristics of shock-induced boundary-layer separation on nacelles under windmilling diversion conditions(AIAA, 2023-11-02) Boscagli, Luca; MacManus, David; Tejero, Fernando; Sabnis, Kshitij; Babinsky, H.; Sheaf, ChristopherThe boundary layer on the external cowl of an aeroengine nacelle under windmilling diversion conditions is subjected to a notable adverse pressure gradient due to the interaction with a near-normal shock wave. Within the context of computational fluid dynamics (CFD) methods, the correct representation of the characteristics of the boundary layer is a major challenge in capturing the onset of the separation. This is important for the aerodynamic design of the nacelle, as it may assist in the characterization of candidate designs. This work uses experimental data obtained from a quasi-2D rig configuration to provide an assessment of the CFD methods typically used within an industrial context. A range of operating conditions are investigated to assess the sensitivity of the boundary layer to changes in inlet Mach number and mass flow through a notional windmilling engine. Fully turbulent and transitional boundary-layer computations are used to determine the characteristics of the boundary layer and the interaction with the shock on the nacelle cowl. The correlation between the onset of shock-induced boundary-layer separation and the preshock Mach number is assessed, and it was found that the CFD is able to discern the onset of boundary-layer separation.Item Open Access Characterization of unsteady distortion events for S-duct intakes under non-uniform inlet conditions(AIAA, 2023-01-19) Migliorini, Matteo; Zachos, Pavlos K.; MacManus, DavidThe use of convoluted intakes is expected to grow in novel aircraft configurations as designers seek to integrate more closely the propulsion system with the airframe. Previous research highlighted considerable unsteady flow distortions for S-duct configurations. However, most of the work was limited to the types of flow distortion inherently generated within the duct which reflects a relatively narrow range of aerodynamic conditions. In addition, the conditions of the flow distortion approaching the propulsion system is still not well understood due to the lack of experimental data and methods for unsteady distortion analysis. Recently, a novel analysis method was developed to consider the unsteady flow distortion from the perspective of an envisaged rotor blade through the exploitation of measurements with high-bandwidth Particle Image Velocimetry. In this study, and with this method, the aim is to provide a more advanced classification of unsteady distortion events based on the distribution of incidence on the envisaged rotor blades. This work can provide guidelines for methods to evaluate peak distortion levels under different inlet configurations for intake-engine integration assessments.Item Open Access A comparative assessment of multi-objective optimisation methodologies for aero-engine nacelles(ICAS, 2022-09-09) Swarthout, Avery; MacManus, David; Tejero, Fernando; Matesanz García, Jesús; Boscagli, Luca; Sheaf, ChristopherThere are significant environmental and economic drivers for the development of more fuel-efficient commercial aircraft engines. The propulsive efficiency benefits of ultra-high bypass ratio turbofans may be counteracted by the drag and weight penalty associated with larger nacelles. A more compact nacelle design may therefore be necessary to reduce these penalties. However, increasing compactness also increases the sensitivity of the nacelle to boundary layer separation under off-design windmilling conditions. This paper investigates methods for incorporating windmilling considerations alongside design point requirements within a multi-objective, multi-point optimisation. Windmilling under aircraft diversion and at the end-of-runway (EoR) condition are considered. The windmilling conditions are assessed through a combination of regression and classification type criteria. The transonic aerodynamics of the nacelle at the design point are notably different from the transonic characteristics at the diversion windmilling conditions. Meanwhile, the aerodynamics, and separation mechanisms, at the end-of-runway condition are dominated by subsonic diffusion. Overall, a combination of regression and classification mechanisms are found to be most suitable for the nacelle optimization as it delivers a design population which is favorably balanced between robustness against boundary layer separation as well as delivering nacelle drag benefits.Item Open Access Data for "SINATRA - Complex intake flow distortion measurements"(Cranfield University, 2024-09-01) Migliorini, Matteo; Doll, Ulrich; Lawson, Nicholas; Melnikov, Sergey M; Steinbock, Jonas; Dues, Michael; Zachos, Pavos; Roehle, Ingo; MacManus, DavidItem Open Access Deep-learning for flow-field prediction of 3D non-axisymmetric aero-engine nacelles(AIAA, 2023-06-08) Tejero, Fernando; MacManus, David; Matesanz García, Jesús; Boscagli, Luca; Hueso Rebassa, Josep; Sheaf, ChristopherComputational fluid dynamics (CFD) methods have been widely used for the design and optimisation of complex non-linear systems. Within this context, the overall process can typically have a large computational overhead. For preliminary design studies, it is important to establish design capabilities that meet the usually conflicting requirements of rapid evaluations and accuracy. Of particular interest is the aerodynamic design of components or subsystems within the transonic range. This can pose notable challenges due to the non-linearity of this flow regime. There is a need to develop low order models for future civil aero-engine nacelle applications. The aerodynamics of compact nacelles can be sensitive to changes in geometry and operating conditions. For example, within the cruise segment different flow-field characteristics may be encountered such as shock-wave boundary layer interaction or shock induced separation. As such, an important step in the successful design of these new architectures is to develop methods for fast and accurate flow-field prediction. This work studies two different metamodelling approaches for flow-field prediction of 3D non-axisymmetric nacelles. Firstly, a reduced order model based on an artificial neural network (ANN) is considered. Secondly, a low order model that combines singular value decomposition and an artificial neural network (SVD+ANN) is investigated. Across a wide geometric design space, the ANN and SVD+ANN methods have an overall uncertainty in the isentropic Mach number prediction of about 0.02. However, the ANN approach has better capabilities to predict pre-shock Mach numbers and shock-wave locations.Item Open Access Deep-learning methods for non-linear transonic flow-field prediction(AIAA, 2023-05-08) Sureshbabu, Sanjeeth; Tejero, Fernando; Sánchez Moreno, Francisco; MacManus, David; Sheaf, ChristopherIt is envisaged that the next generation of ultra-high bypass ratio engines will use compact aero-engine nacelles. The design and optimisation process of these new configurations have been typically driven by numerical simulations, which can have a large computational cost. Few studies have considered the nacelle design process with low order models. Typically these low order methods are based on regression functions to predict the nacelle drag characteristics. However, it is also useful to develop methods for flow-field prediction that can be used at the preliminary design stages. This paper investigates an approach for the rapid assessment of transonic flow-fields based on convolutional neural networks (CNN) for 2D axisymmetric aeroengine nacelles. The process is coupled with a Sobel filter for edge detection to enhance the accuracy in the prediction of the shock wave location. Relative to a baseline CNN built with guidelines from the open literature, the proposed method has a 75% reduction in the mean square error for Mach number prediction. Overall, the presented method enables the fast prediction of the flow characteristics around civil aero-engine nacelles.Item Open Access Design and optimisation of a Mach 2.5 wind tunnel nozzle(AIAA, 2023-01-19) Moreno, Miguel; Migliorini, Matteo; Zachos, Pavlos K.; Haslam, Anthony; MacManus, DavidThe paper presents a methodology for the numerical design and optimization of a distortion-free two-dimensional Mach 2.5 nozzle based on a parametric model. The non-uniformities generated at the Mach wave reflections downstream of the nozzle throat that the Method of Characteristics only partially addresses are minimized. The spatial discretization of the domain is integrated with the boundary layer analysis for fast and robust data processing, especially in the final viscous sublayers in the transition regions within the bulk of the fluid. The flow patterns and corner flows of the supersonic nozzle are assessed via three-dimensional high-fidelity computational fluid dynamics. As a result, a fast workflow for nozzle design to meet prescribed flow quality requirements is herein illustrated.Item Open Access Design of a high-speed intake distortion simulator for propulsion integration research(AIAA, 2023-01-19) Migliorini, Matteo; Szymanski, Artur; Zachos, Pavlos K.; MacManus, David; Martin, Peter G.High levels of inlet flow distortion can be a critical aspect in supersonic air induction systems due to the complex spatial nature and notable temporal unsteadiness. This can affect the operability and performance of the propulsion system. Simulation of the intake shock system in a relatively less expensive, lower technology readiness level experimental facility can be an important element to mitigate a significant part of the risk that industrial and certification testing carries. The work described in this paper is part of a programme that aims to develop such a distortion simulation test rig where the capability of advanced non-intrusive measurement techniques would be applied in propulsion integration research. The paper describes the concept, preliminary design and sizing of the working section of the rig, the exhaust system design and the integration of the test model. A brief summary of the rig architecture is provided along with details of the high-pressure system that drives the supersonic flow. The work indicates that careful design of the working section is required to ensure sufficient operating range and representative aerodynamics of the test model. It is also shown that the working section wall interference on the test model is tightly linked with the type and size of the aircraft intake to be tested. Ways to mitigate this interference are herein explored.Item Open Access Design of a new test rig to investigate transonic external fan cowl separation(Association Aeronautique Astronautique de France, 2022-03-28) Sabnis, Kshitij; Boscagli, Luca; Swarthout, Avery; Babinsky, Holger; MacManus, David; Sheaf, Christopher T.Ultra high-bypass ratio engines, which show considerable promise in reducing the environmental impact of commercial aviation, generally adopt slim fan cowl profiles. These geometries can be more sensitive to separation on the external surfaces in engine windmilling conditions during take-off climb out or during cruise. This paper describes the development of a two-dimensional wind tunnel rig which can accurately replicate the separation mechanisms experienced by real aero-engine nacelles. This design process highlights the importance of considering factors such as Reynolds-number effects, tunnel-wall effects, the two-dimensional nature of the rig, and the tunnel boundary layers.Item Open Access Design optimisation of non-axisymmetric exhausts for installed civil aero-engines(Elsevier, 2023-10-31) Hueso Rebassa, Josep; MacManus, David; Tejero, Fernando; Goulos, Ioannis; Sánchez-Moreno, F.; Sheaf, ChristopherFuture civil aero-engines are likely to operate with higher bypass-ratios (BPR) than current power-plants to improve propulsive efficiency and reduce specific thrust. This will probably be accompanied by an increase of fan diameter and size of the power plant. Consequently, future configurations are likely to require more close-coupled installations with the airframe due to structural and ground clearance requirements. This tendency may lead to an increase in the adverse installation effects which could be mitigated with non-axisymmetric exhausts. However, due to the prohibitive computational cost, limited regions of the design space have been studied. For this reason, a relatively low-cost design approach for the integrated system is required. The aim of this work is to establish a method to map the non-axisymmetric exhaust design space where the effects of the propulsion system installation are taken into account. The methodology relies on the generation of a design database using inviscid computational fluid dynamics (CFD) methods. This is used to characterise the design space, identify the dominant design parameters and build response surface models for optimisation. The candidate designs that arise from the optimisation are assessed with viscous CFD simulations to assess the aerodynamic mechanisms and performance characteristics. The result is a set of design recommendations for installed configurations with non-axisymmetric exhausts. The method is an enabler for the optimisation of installed propulsion systems and has provided an exhaust design with a 0.7% improvement on net vehicle force relative to an axisymmetric exhaust, for a close coupled configuration where the fan cowl is overlapped with the wing. A reduction in net vehicle force is expected to lead to a similar reduction in cruise fuel burn.Item Open Access Experimental investigation of transonic external fan cowl separation(Association Aeronautique Astronautique de France, 2023-03-29) Sabnis, Kshitij; Boscagli, Luca; Babinsky, Holger; MacManus, David; Sheaf, Christopher T.When a civil aircraft engine is shut down during the cruise phase of flight and thus begins to windmill, a supersonic region forms on the external surface of the fan cowl. The terminating normal shock can separate the turbulent boundary layer developing on this external surface. A series of experiments are performed in a quasitwo-dimensional wind tunnel rig to investigate the influence of various parameters on this flow problem. As the engine mass-flow rate is reduced, an increase in normal shock strength results in the onset of flow separation which thickens the boundary layer developing on the external fan cowl surface by a factor of three. A reduction in incoming Mach number from the nominal value of 0.65 to 0.60 weakens the shock wave and thus delays flow separation. If the incoming boundary layer is laminar rather than turbulent, the normal shock Mach number is observed to increased by 10%. Despite the stronger shock, no significant flow separation can be detected even for the lowest engine mass-flow rates studied and the external nacelle surface boundary layer is measured to be thinner than for the turbulent case.Item Open Access Fan-intake aerodynamic interactions under crosswind conditions(European Turbomachinery Society, 2023-04-28) Boscagli, Luca; MacManus, David; Christie, RobertThe aerodynamics of an aero-engine intake under off-design conditions is characterized by a range of steady and unsteady mechanisms that can adversely affect the fan operability. A hierarchical computational fluid dynamics approach was used for an initial assessment of the primary aerodynamic interactions between the fan and the intake design. These approaches included steady computations with a lower order fan model as well as full unsteady computations. For a powered intake in crosswind, the direction of the wind determines the direction of rotation of the ground vortex relative to the fan. For the full unsteady analyses, the threshold crosswind speed reduced by 12kts and 22kts relative to the steady analysis for the counter-rotating and co-rotating configuration respectively. Overall, this work identified and assessed for the first time a fan-intake unsteady aerodynamic interactions that may affect the design of short intakes in association with fan systems.Item Open Access Heat exchanger integration with an aero-engine bypass duct(Council of European Aerospace Societies (CEAS), 2023-07-13) Bajimaya, Raul; MacManus, David; Abdessemed, Chawki; Goulos, Ioannis; Matesanz García, Jesús; Sheaf, Christopher; Kyritsis, VasileiosThe development of aero engines with geared fans may require the use of a heat exchanger system embedded within the bypass duct to dissipate heat due to the losses within the power gearbox of the fan. It is pertinent that the naturally ventilated heat exchanger system (HEX) is designed and installed to minimise detrimental impacts on the performance of the engine while meeting the HEX heat transfer requirements. This paper demonstrates the capabilities of a coupled mixed fidelity method to model a ventilated HEX embedded within the bypass duct. A systematic approach is presented to quantify the sensitivity of HEX heat transfer, HEX volume and engine net thrust to perturbation in HEX overall size and integration. A method to explore and quantify the trade-offs in HEX performance and bypass performance is detailed. The method can be used to allow rapid assessment of the integration of the HEX with the bypass duct.Item Open Access High-resolution turbofan intake flow characterization by automated stereoscopic-PIV in an industrial wind tunnel environment(IOP Publishing, 2023-11-30) Kempaiah, Kushal U.; Piovesan, Tommaso; Zachos, Pavlos K.; Michaelis, Dirk; Gebbink, Roy; van Rooijen, Bart; Prieto, Daniel Gil; MacManus, David; Sciacchitano, Andrea; Sheaf, ChristopherUnsteady inlet flow distortion can influence the stability and performance of any propulsion system, in particular for more novel, short and slim intakes of future aero-engine configurations. As such, the requirement for measurement methods able to provide high spatial resolution data is important to aid the understanding of these flow fields. This work presents flow field characterisations at a crossflow plane within a short aeroengine intake using stereoscopic particle image velocimetry (SPIV). A series of tests were conducted across a range of crosswind and high angle of attack conditions for a representative short and slim aspirated intake configuration at two operating points in terms of mass flow rate. The velocity maps were measured at a crossflow plane within the intake at an axial position L/D = 0.058 from where a fan is expected to be installed. The diameter of the measurement plane was 250 mm, and the final spatial resolution of the velocity fields had a vector pitch of 1.5 mm which is at least two orders of magnitude richer than conventional pressure-based distortion measurements. The work demonstrates the ability to perform robust non-intrusive flow measurements within modern intake systems in an industrial wind tunnel environment across a wide range of operating conditions; hence, it is suggested that SPIV can potentially become part of standard industrial testing. The results provide rich datasets that can notably improve our understanding of unsteady distortions and influence the design of novel, closely coupled engine-intake systems.Item Open Access Impact of installation on the performance of a civil turbofan exhaust at wind-milling: a combined experimental and numerical approach(Elsevier, 2025-03) Goulos, Ioannis; MacManus, David; Hueso Rebassa, Josep; Alderman, James; Sheaf, ChristopherThis work presents a combined experimental and numerical investigation of the effect of wing integration on the aerodynamic behaviour of a typical large civil aero-engine exhaust at wind-milling conditions. Engine performance simulations established estimates of Fan and Core Nozzle Pressure Ratios (FNPR and CNPR, respectively) for representative “engine-out” wind-milling scenarios. The experimental data and Reynolds Averaged Navier Stokes (RANS) Computational Fluid Dynamic (CFD) simulations encompassed End of Runway (EoR) take-off, diversion, and cruise wind-milling conditions for both isolated and installed configurations. The impact of FNPR, CNPR, free-stream Mach number (M∞), and high-lift surfaces on the installed suppression effect were evaluated. The measured and CFD predicted fan and core nozzle maps were implemented into the engine performance model to estimate the engine re-matching characteristics due to the impact of the installation, and the effect on engine mass flow. The effect of installation can reduce the fan and core nozzle discharge coefficients by up to 13% and 26%, respectively, relative to the isolated configuration for representative EOR wind-milling conditions. RANS CFD captures the effect of suppression on both the fan and core with an accuracy between 0.1% and 1.2%, depending on Mach number, which is sufficient for industrial design and analysis purposes. The engine performance analyses showed that the installed suppression effect can result in a 10% reduction of engine mass flow at EOR wind-milling. Within the context of nacelle design under wind-milling, this effect of exhaust suppression must be considered in determining the intake Mass Flow Capture Ratio (MFCR).Item Open Access Impact of installation on the performance of an aero-engine exhaust at wind-milling flow conditions(American Society of Mechanical Engineers, 2024-02-01) Goulos, Ioannis; MacManus, David; Hueso Rebassa, Josep; Tejero, Fernando; Au, Andy; Sheaf, ChristopherThis paper presents a numerical investigation of the effect of wing integration on the aerodynamic behavior of a typical large civil aero-engine exhaust system at wind-milling flow conditions. The work is based on the dual stream jet propulsion (DSJP) test rig, as will be tested within the transonic wind tunnel (TWT) located at the aircraft research association (ARA) in the UK. The DSJP rig was designed to measure the impact of the installed pressure field due to the effect of the wing on the aerodynamic performance of separate-jet exhausts. The rig is equipped with the dual separate flow reference nozzle (DSFRN), installed under a swept wing. Computational fluid dynamic simulations were carried out for representative ranges of fan and core nozzle pressure ratios (CNPR) for “engine-out” wind-milling scenarios at end of runway (EOR) takeoff, diversion, and cruise conditions. Analyses were done for both isolated and installed configurations to quantify the impact of the installed pressure field on the fan and core nozzle discharge coefficients. The impact of fan and core nozzle pressure ratios, as well as freestream Mach number and high-lift surfaces on the installed suppression effect, was also evaluated. It is shown that the installed pressure field can reduce the fan nozzle discharge coefficient by up to 16%, relative to the isolated configuration for EOR wind-milling conditions. The results were used to inform the design and setup of the experimental activity which is planned for 2023.Item Open Access Nacelle optimisation through multi-fidelity neural networks(Emerald, 2024-07-25) Sánchez-Moreno, Francisco; MacManus, David; Tejero, Fernando; Sheaf, ChristopherPurpose Aerodynamic shape optimisation is a complex problem usually governed by transonic non-linear aerodynamics, a high dimensional design space and high computational cost. Consequently, the use of a numerical simulation approach can become prohibitive for some applications. This paper aims to propose a computationally efficient multi-fidelity method for the optimisation of two-dimensional axisymmetric aero-engine nacelles. Design/methodology/approach The nacelle optimisation approach combines a gradient-free algorithm with a multi-fidelity surrogate model. Machine learning based on artificial neural networks (ANN) is used as the modelling technique because of its ability to handle non-linear behaviour. The multi-fidelity method combines Reynolds-averaged Navier Stokes and Euler CFD calculations as high- and low-fidelity, respectively. Findings Ratios of low- and high-fidelity training samples to degrees of freedom of nLF/nDOFs = 50 and nHF/nDOFs = 12.5 provided a surrogate model with a root mean squared error less than 5% and a similar convergence to the optimal design space when compared with the equivalent CFD-in-the-loop optimisation. Similar nacelle geometries and aerodynamic flow topologies were obtained for down-selected designs with a reduction of 92% in the computational cost. This highlights the potential benefits of this multi-fidelity approach for aerodynamic optimisation within a preliminary design stage. Originality/value The application of a multi-fidelity technique based on ANN to the aerodynamic shape optimisation problem of isolated nacelles is the key novelty of this work. The multi-fidelity aspect of the method advances current practices based on single-fidelity surrogate models and offers further reductions in computational cost to meet industrial design timescales. Additionally, guidelines in terms of low- and high-fidelity sample sizes relative to the number of design variables have been established.