CERES :: Browsing by Author "Sheaf, Christopher T."

Browsing by Author "Sheaf, Christopher T."

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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 (ASME), 2016-03-15) Goulos, Ioannis; Otter, John; Stankowski, Tomaz; MacManus, David G.; Grech, Nicholas; Sheaf, Christopher T.
The 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).
Open Access
Aerodynamics of high-bypass-ratio aeroengine nacelles: numerical and experimental investigation
(American Institute of Aeronautics and Astronautics (AIAA), 2025-03-12) Tejero, Fernando; MacManus, David G.; Sanchez-Moreno, Francisco; Schreiner, Deneys; Hill, Andrea; Sheaf, Christopher T.; Ramirez-Rubio, Santiago
This work presents a numerical and experimental investigation of the nacelle aerodynamics for high-bypass- ratio aeroengines. A conventional nacelle that is representative of a current standard, and a compact design that is envisaged for future aeroengines, were optimized with an existing computational method. Both nacelles were tested in a large-scale transonic wind tunnel. For the first time, the aerodynamic benefits of compact nacelles are demonstrated through an experimental test campaign. Measurements and computational fluid dynamics (CFD) simulations confirmed the drag reduction of compact configurations across a wide range of operating points with different flight Mach numbers, mass-flow capture ratios, and angles of attack. For midcruise conditions with a Mach number of 0.85, this was a drag reduction of 8.5% and 8.8% for the measurements and CFD, respectively. These benefits are similar to an isolated optimization, that is, not installed in the wind tunnel, which confirmed the capabilities of the method to identify the drag benefit of compact designs. Relative to the measurements, the main aerodynamic characteristics on the nacelles were captured by CFD in terms of isentropic Mach number distributions and shock location. This work provides a quantitative evaluation for the use of CFD within an industrial setting for nacelle design and analysis.
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 G.; 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.
Open Access
Characteristics of shock-induced boundary-layer separation on nacelles under windmilling diversion conditions
(AIAA, 2024-01) Boscagli, Luca; MacManus, David G.; Tejero, Fernando; Sabnis, Kshitij; Babinsky, H.; Sheaf, Christopher T.
The 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.
Open Access
A comparative assessment of multi-objective optimisation methodologies for aero-engine nacelles
(ICAS, 2022-09-09) Swarthout, Avery E.; MacManus, David G.; Tejero, Fernando; Matesanz García, Jesús; Boscagli, Luca; Sheaf, Christopher T.
There 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.
Open Access
Deep-learning for flow-field prediction of 3D non-axisymmetric aero-engine nacelles
(AIAA, 2023-06-08) Tejero, Fernando; MacManus, David G.; Matesanz García, Jesús; Boscagli, Luca; Hueso Rebassa, Josep; Sheaf, Christopher T.
Computational 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.
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 G.; Sheaf, Christopher T.
It 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.
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 E.; Babinsky, Holger; MacManus, David G.; 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.
Open Access
Design optimisation of non-axisymmetric exhausts for installed civil aero-engines
(Elsevier, 2023-10-31) Hueso Rebassa, Josep; MacManus, David G.; Tejero, Fernando; Goulos, Ioannis; Sánchez-Moreno, F.; Sheaf, Christopher T.
Future 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.
Open Access
Experimental investigation of external fan cowl separation for compact nacelles in windmilling scenarios
(AIAA, 2023-06-08) Sabnis, Kshitij; Boscagl, Luca; Babinsky, Holger; MacManus, David G.; Sheaf, Christopher T.
The slim fan cowl profiles used for ultra-high bypass ratio aircraft engines are designed considering off-design operating conditions, such as engine windmilling during take-off climb out or during cruise. The current paper describes wind tunnel experiments studying how incoming Mach number and engine mass-flow rate influence the aerodynamics governing external fan cowl flow separation in both these windmilling scenarios. A transonic region may form on the forebody surface if the engine becomes inoperative during take-off climb out, with peak Mach number up to 1.2. The subsequent adverse pressure gradient can separate the local boundary layer, resulting in flow separation which originates near the highlight and a more uniform fan cowl pressure distribution. Meanwhile, engine shut down during cruise results in a large supersonic region on the external fan cowl surface which terminates in a normal shock wave. When the Mach number of this shock exceeds about 1.35, a closed separation bubble develops, which causes up to a four-fold increase in the boundary-layer thickness downstream of the shock wave.
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 G.; 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.
Open Access
Heat exchanger integration with an aero-engine bypass duct
(Council of European Aerospace Societies (CEAS), 2023-07-13) Bajimaya, Raul; MacManus, David G.; Abdessemed, Chawki; Goulos, Ioannis; Matesanz García, Jesús; Sheaf, Christopher T.; Kyritsis, Vasileios
The 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.
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 G.; Sciacchitano, Andrea; Sheaf, Christopher T.
Unsteady 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.
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 G.; Hueso Rebassa, Josep; Alderman, James; Sheaf, Christopher T.
This 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).
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 G.; Hueso Rebassa, Josep; Tejero, Fernando; Au, Andy; Sheaf, Christopher T.
This 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.
Open Access
Nacelle optimisation through multi-fidelity neural networks
(Emerald, 2024-07-25) Sánchez-Moreno, Francisco; MacManus, David G.; Tejero, Fernando; Sheaf, Christopher T.
Purpose 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.
Open Access
Optimization of installed compact and robust nacelles using surrogate models
(ICAS, 2022) Sanchez Moreno, Francisco; MacManus, David G.; Hueso Rebassa, Josep; Tejero, Fernando; Sheaf, Christopher T.
The design and optimization of aero-engine nacelles in a configuration installed on the airframe may be an important consideration to realize the cycle benefits of new ultra-high bypass ratio aero-engines. However, this is typically a high-dimensional design problem and there is a need to reduce the associated computational costs. This work presents a method for aerodynamic nacelle optimization for an installed configuration and provides further knowledge about the characteristics of this design space. The methodology includes single fidelity surrogate models built with inviscid flow solutions. Gaussian process regression and artificial neural networks are tested as modelling techniques. Viscous computations are used to assess the optimized designs at cruise and off-design windmilling diversion condition. This approach yielded an optimal design with a reduction in fuel burn of about 0.56% relative to a design optimized in isolated configuration without considering the powerplant integration effects. The optimal design also met the robustness criteria in terms of limited flow separation at the windmilling diversion conditions.
Open Access
Propulsion integration study of civil aero-engine nacelles
(Cambridge University Press, 2023-06-13) Tejero, Fernando; MacManus, David G.; Goulos, Ioannis; Sheaf, Christopher T.
It is envisaged that future civil aero-engines will operate with ultra-high bypass ratios to reduce the specific fuel consumption. To achieve the expected benefits from the new engine cycles, these new powerplants may mount compact nacelles. For these new configurations the aerodynamic coupling between the powerplant and the airframe may increase. For this reason, it is required to quantify and further understand the effects of aircraft integration for compact aero-engine nacelles. This study provides an insight of the changes in flow aerodynamics as well as quantification of the most relevant performance metrics of the powerplant, airframe and the combined aircraft system across a range of different installation positions. Relative to a conventional architecture, there is an aerodynamic benefit in net vehicle force of about 1.2% for a compact powerplant when installed in forward positions. This is the same improvement that was identified when the aero-engine nacelles were in isolation. However, for close-coupled installation positions, the aerodynamic benefit in net vehicle force erodes to 0.44% due to the larger effects of aircraft integration on compact nacelles.
Open Access
Shock-induced fan cowl separation during aeroengine windmilling at diversion from cruise
(AIAA, 2025-03) Sabnis, Kshitij; Babinsky, Holger; Boscagli, Luca; MacManus, David G.; Sheaf, Christopher T.
When a civil aircraft engine is operated at windmill during the cruise flight phase, there is supersonic flow acceleration around the leading edge of the fan cowl toward the external surface. The terminating normal shock wave can separate the turbulent boundary layer developing on this external surface. A series of experiments at a flight-relevant Reynolds number (1.2 million based on lip thickness) are performed in a quasi-two-dimensional wind tunnel rig to investigate the underlying flow physics. At a nominal inflow Mach number of 0.65 and a nacelle incidence angle of 4.5 deg, as the equivalent engine mass-flow rate is reduced, an increase in shock strength results in flow separation when the shock exceeds Mach 1.4. Over a 10% range in the notional engine mass-flow rate, the boundary layer developing on the external fan cowl thickens by a factor of three on the onset of separation. A reduction in the incoming Mach number from 0.65 to 0.60 weakens the shock wave and thus delays separation. An increase in surface roughness has no significant effect in situations where the boundary layer remains attached. However, for separated cases, an increased local roughness height causes a greater separation extent and a thicker boundary layer downstream of the shock wave.
Open Access
Towards the design and optimisation of future compact aero-engines: intake/fancowl trade-off investigation
(Emerald, 2022-12-09) Tejero, Fernando; MacManus, David G.; Matesanz García, Jesús; Swarthout, Avery E.; Sheaf, Christopher T.
Purpose Relative to in-service aero-engines, the bypass ratio of future civil architectures may increase further. If traditional design rules are applied to these new configurations and the housing components are scaled, then it is expected that the overall weight, nacelle drag and the effects of aircraft integration will increase. For this reason, the next generation of civil turbofan engines may use compact nacelles to maximise the benefits from the new engine cycles. The purpose of this paper is to present a multi-level design and optimisation process for future civil aero-engines. Design/methodology/approach An initial set of multi-point, multi-objective optimisations for axisymmetric configurations are carried out to identify the trade-off between intake and fancowl bulk parameters of highlight radius and nacelle length on nacelle drag. Having identified the likely optimal part of the design space, a set of computationally expensive optimisations for three-dimensional non-axisymmetric configurations is performed. The process includes cruise- and windmilling-type operating conditions to ensure aerodynamic robustness of the downselected configurations. Findings Relative to a conventional aero-engine nacelle, the developed process yielded a compact aero-engine configuration with mid-cruise drag reduction of approximately 1.6% of the nominal standard net thrust. Originality/value The multi-point, multi-objective optimisation is carried out with a mixture of regression and classification functions to ensure aerodynamic robustness of the downselected configurations. The developed computational approach enables the optimisation of future civil aero-engine nacelles that target a reduction of the overall fuel consumption.