CERES :: Browsing by Author "Tejero, Fernando"

Browsing by Author "Tejero, Fernando"

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Open Access
Aerodynamic optimisation of civil aero-engine nacelles by dimensionality reduction and multi-fidelity techniques
(Unknown, 2022-03-30) Tejero, Fernando; MacManus, David G.; Hueso Rebassa, Josep; Sanchez Moreno, Francisco; Goulos, Ioannis; Sheaf, Christopher
Aerodynamic shape optimisation is complex due to the high dimensionality of the problem, the associated nonlinearity and its large computational cost. These three aspects have an impact on the overall time of the design process. To overcome these challenges, this paper develops a method for transonic aerodynamic design with dimensionality reduction and multi-fidelity techniques. It is used for the optimisation of an installed civil ultra-high bypass ratio aero-engine nacelle. As such, the effects of airframe-engine integration are considered during the optimisation routine. The active subspace method is applied to reduce the dimensionality of the problem from 32 to 2 design variables with a database compiled with Euler CFD calculations. In the reduced dimensional space, a co-Kriging model is built to combine Euler lower-fidelity and RANS higher-fidelity CFD evaluations. Relative to a baseline aero-engine nacelle derived from an isolated optimisation process, the proposed method yielded a non-axisymmetric nacelle configuration with an increment in net vehicle force of 0.65% of the nominal standard net thrust. This work demonstrates that the developed methodology enables the optimisation of complex aerodynamic problems.
Open Access
Aerodynamic optimisation of civil aero-engine nacelles by dimensionality reduction and multi-fidelity techniques
(Emerald, 2022-09-30) Tejero, Fernando; MacManus, David G.; Hueso Rebassa, Josep; Sanchez Moreno, Francisco; Goulos, Ioannis; Sheaf, Christopher
Purpose - Aerodynamic shape optimisation is complex due to the high dimensionality of the problem, the associated non-linearity and its large computational cost. These three aspects have an impact on the overall time of the design process. To overcome these challenges, this paper develops a method for transonic aerodynamic design with dimensionality reduction and multi-fidelity techniques. Design/methodology/approach - The developed methodology is used for the optimisation of an installed civil ultra-high bypass ratio aero-engine nacelle. As such, the effects of airframe-engine integration are considered during the optimisation routine. The active subspace method is applied to reduce the dimensionality of the problem from 32 to 2 design variables with a database compiled with Euler CFD calculations. In the reduced dimensional space, a co-Kriging model is built to combine Euler lower-fidelity and RANS higher-fidelity CFD evaluations. Findings - Relative to a baseline aero-engine nacelle derived from an isolated optimisation process, the proposed method yielded a non-axisymmetric nacelle configuration with an increment in net vehicle force of 0.65% of the nominal standard net thrust. Originality - This work investigates the viability of CFD optimisation through a combination of dimensionality reduction and multi-fidelity method, and demonstrates that the developed methodology enables the optimisation of complex aerodynamic problems.
Open Access
Aerodynamics of a compact nacelle at take-off conditions
(IEEE, 2023-06-08) Swarthout, Avery E.; MacManus, David G.; Tejero, Fernando; Matesanz García, Jesús; Goulos, Ioannis; Boscagli, Luca; Sheaf, Christopher
Next generation ultra-high bypass ratio turbofans may have larger fan diameters than the previous generation of aircraft engines. This will potentially increase the nacelle diameter and may incur penalties to the weight and drag of the powerplant. To offset these penalties, a more compact nacelle may be used. Compact nacelles may be more sensitive to boundary layer separation at the end-of-runway conditions, particularly at an off-design windmilling operating point. Additionally, the flow separation on the external cowl surface is likely to be influenced by the integration between the powerplant, pylon and airframe. The publicly available NASA high lift common research model (HL-CRM) with take-off flap and slat settings was modified to accommodate an ultra-high bypass ratio powerplant. The powerplant has an intake, separate jet exhaust, external cowl and pylon. Boundary layer separation on the external cowl of the compact powerplant is assessed at end-of-runway rated take-off and take-off windmilling scenarios. Additionally, the lift curve and Cp distributions of the high lift common research model (HL-CRM) are compared for rated take-off and take-off windmilling engine mass flows. Overall, the nacelle boundary layer separates from the nacelle highlight at windmilling conditions when the engine mass flow is relatively low. The mechanism of separation at windmilling conditions is diffusion driven and is initiated on the nacelle aft-body. The pylon has a small impact on the overall mechanism of separation. However, the wing and high-lift devices of the HL-CRM introduce local separation on the external cowl. The HL-CRM wing with the installed powerplant stalls at a similar angle (αa/c = 16°) to the HL-CRM with the through flow nacelle available in the open literature. Compared with the nominal take-off condition, the maximum lift coefficient of the HL-CRM airframe was reduced by about 2% under windmilling engine mass flows.
Open Access
Aerodynamics of a short intake at high incidence
(European Turbomachinery Society, 2025-03-28) Tejero, Fernando; MacManus, David G.; Hueso Rebassa, Josep; Frey Marioni, Yuri; Bousfield, Ian
This work assesses the aerodynamics of a short aero-engine intake for a new rig that is planned to be tested at the Large Low-Speed Facility of the German Dutch Wind Tunnels (LLF-DNW) in 2025. A range of computations were performed to assess if the expected aerodynamics in this arrangement encompass the envisaged range of flow field characteristics of the equivalent isolated configuration. The effect of massflow capture ratio and angle of attack are investigated. In addition, an intake flow separation taxonomy is proposed to characterize the associated flows. The wind tunnel analysis is based on two different modelling approaches: an aspirated isolated intake and a coupled fan-intake configuration. The coupled configuration uses a full annulus model with a harmonic mixing plane method. Across the range of operating conditions with changes in massflow capture ratio and angle of attack, there are attached and separated flows. The main separation mechanisms are diffusion-driven and shock-induced, which shows the different aerodynamics that may be encountered in a short intake. Overall, this work provides an initial evaluation of the aerodynamics of the new fan/intake test rig configuration, provides guidance for the wind tunnel testing, and lays a foundation for subsequent unsteady coupled fan-intake studies.
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
An automated approach for the aerodynamic design of close-coupled propulsion/airframe configurations
(Council of European Aerospace Societies (CEAS), 2020-02-28) Matesanz García, Jesús; Christie, Robert; Tejero, Fernando; MacManus, David G.; Heidebrecht, Alexander
Reducing aircraft emissions is a key element in mitigating the environmental impact of aviation. Within this context, different novel aircraft propulsion configurations have been proposed. A common feature of many of these novel configurations is the closer integration of the propulsive system and the aircraft airframe with an expected increase of the aerodynamic coupling. Therefore, is necessary to assess the performance of the aerodynamic installation of the propulsive system of these configurations with a systematic approach. A systematic and automated methodology for the design and performance evaluation of embedded propulsion systems is defined. This methodology is demonstrated with a Boundary Layer Ingestion propulsive fuselage concept. This approach covers the geometry design of the selected configuration, an automatic aerodynamic numerical computation and a novel performance evaluation for the design. A Design Space Exploration was performed to characterize the relative importance of the individual parameters of the geometry and their correlation with the key performance metrics. Finally, a multi-objective optimization was carried to demonstrate the capabilities of this approach.
Open Access
Characteristics of shock-induced boundary layer separation on nacelles under windmilling diversion conditions
(AIAA, 2023-06-08) Boscagli, Boscagli; MacManus, David G.; Tejero, Fernando; Sabnis, Kshitij; Babinsky, Holger; Sheaf, Christopher
The boundary layer on the external cowl of an aero-engine 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 to capture 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 is 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 pre-shock Mach number is assessed and the boundary layer integral characteristics ahead of the shock and the post-shock recovery evaluated and quantified. Overall, it was found that the CFD is able to discern the onset of boundary layer separation for a nacelle under windmilling conditions.
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
Civil turbofan propulsion aerodynamics: thrust-Drag accounting and impact of engine installation position
(Elsevier, 2021-01-28) Goulos, Ioannis; John Otter, John J.; Tejero, Fernando; Hueso Rebassa, Josep; MacManus, David G.
It is envisaged that the next generation of civil aero-engines will employ high bypass ratios to lower specific thrust and improve propulsive efficiency. This trend is likely to be accompanied with the integration of compact nacelle and exhausts in podded under-wing installation positions that are close coupled to the airframe. This leads to the requirement for a comprehensive methodology able to predict aerodynamic performance for combined airframe-engine architectures. This paper presents a novel thrust and drag accounting approach for the aerodynamic analysis of integrated airframe-engine systems. An integral metric is synthesised based on the concept of net vehicle force. This is accomplished through the consolidation of aerodynamic coefficients, combined with the engine cycle characteristics obtained from a thermodynamic matching model. The developed approach is coupled with an in-house tool for the aerodynamic design and analysis of installed aero-engines. This framework is deployed to quantify the impact of engine installation position on the aerodynamic performance of a future large turbofan installed on a commercial wide-body airframe. The governing flow mechanisms are identified and their influence is decomposed in terms of the impact on airframe, nacelle, and exhaust performance. It is shown that it is essential to include the impact of installation on the exhaust for the correct determination of overall airframe-engine performance. The difference in net vehicle force for a close coupled position can reach up to -0.70% of nominal standard net thrust relative to a representative baseline engine location.
Open Access
Cluster-based tracking method for the identification and characterisation of vortices
(Association Aéronautique et Astronautique de France (3AF), 2025-03-26) Ibanez, Claudia; Migliorini, Matteo; Giannouloudis, Alexandros; Tejero, Fernando; Zachos, Pavlos K.
An unsupervised, flow-agnostic and automatic cluster-based tracking algorithm for the segmentation of vortex-dominated flows has been successfully developed. It combines the Rortex method and density-based clustering algorithms. The Rortex method differs shear from rotation and overcomes the sensitivity to user-defined thresholds that characterises current practice of vortex identification methods. The algorithm is demonstrated with experimental Stereoscopic Particle Image Velocimetry data from two cases; a high-Reynolds (≈ 106) vortex generated by a half-delta wing, and distorted flow in a scaled-model of a civil aero-engine intake under cross-wind conditions. The approach is a successful method for the segmentation of complex vortical flows under a wide range of conditions.
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
Coupled propulsive and aerodynamic analysis of an installed ultra-high bypass ratio powerplant at high-speed and high-lift conditions
(AIAA, 2023-06-08) Matesanz García, Jesús Matesanz; MacManus, David G.; Tejero, Fernando; Goulos, Ioannis; Hueso Rebassa, Josep; Swarthout, Avery E.; Christie, Robert
To achieve the targets proposed in the Flightpath 2050 for the aviation industry, more efficient propulsive systems are required. One possible solution is to increase the bypass ratio of the engines to increase the propulsive efficiency and reduce the specific fuel consumption. However, larger fan diameters are expected for these configurations, which results in an increase in the aerodynamic coupling between the powerplant and the airframe. The aim of this work is to develop and demonstrate a thrust and lift matching methodology for installed powerplants using a coupled aero-propulsive model. As a proof of concept, the aerodynamic performance of an ultra-high bypass ratio powerplant integrated with the airframe was evaluated across different flight conditions. This includes high-lift operating conditions such as end of runway; and high-speed conditions such as mid cruise. To evaluate the aerodynamic performance of the propulsion integration a combined assessment of the airframe and powerplant aerodynamics is required using computational fluid dynamics (CFD). The integration of the powerplant with the airframe has the potential to change the engine requirements across the aircraft operational envelope. To account for this the aerodynamic analysis is coupled with a turbomachinery model to adjust the engine thermodynamic conditions at a given operating point.
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 considerations of non-axisymmetric exhausts for large civil aero-engines
(AIAA, 2023-06-08) Hueso Rebassa, Josep; MacManus, David G.; Goulos, Ioannis; Tejero, Fernando
In order to reduce fuel consumption, the next generation of aero-engines are expected to operate with higher bypass ratios and lower fan pressure ratios. This will improve the propulsive efficiency of the power plant and reduce specific fuel consumption. Higher bypass ratios will be mostly accommodated with larger fan diameters. However, this will increase the size and mass of the powerplant, which could penalise the overall aircraft drag and erode some of the aero-engine cycle benefits. In addition, future configurations may require more close-coupled installations with the airframe due to structural and ground clearance requirements. This tendency may further exacerbate the adverse aerodynamic installation effects. A better integration of UHBR aero-engines with the airframe could be achieved with non-axisymmetric separate-jet exhausts. Non-axisymmetric configurations of the bypass nozzle can improve the performance of the aircraft by mitigating some of the penalising aerodynamic effects induced by the installation of the power plant. In this context, three-dimensional configurations of exhaust systems are parametrised and integrated with the propulsion system through a refined control of the geometry. The power plant is installed on the NASA Common Research Model and assessed with CFD. The design of non-axisymmetric exhausts is embedded in a relatively low-cost optimisation process. The method is based on response surface models and targets the optimisation of the aircraft net vehicle force for different design concepts of non-axisymmetric exhaust systems and several installation configuration. It is concluded that the optimisation of installed non-axisymmetric exhausts can benefit the overall aircraft net vehicle force between 0.5-0.9% of the engine nominal thrust, depending on the installation position.
Open Access
Design of a quasi-2D rig configuration to assess nacelle aerodynamics under windmilling conditions
(AIAA, 2023-06-08) Boscagli, Luca; Tejero, Fernando; Swarthout, Avery E.; MacManus, David G.; Sabnis, Kshitij; Babinsky, Holger; Sheaf, Christopher
Aero-engine nacelles are typically designed to fulfil both design and off-design aircraft manoeuvres. Under-off design conditions one of the objective is to avoid large flow separation either on the external cowl or within the intake that can influence aircraft and engine operability. One particular scenario is represented by a low engine mass flow regime associated with one inoperative engine, also known as a windmilling condition. Under windmilling, the boundary layer on the external cowl of the nacelle can separate either due to the interaction with shockwaves or due to notable adverse pressure gradient towards the trailing edge. Both mechanisms are computationally difficult to model and there is a need for more validation of computational fluid dynamics (CFD) methods. The aim of this work is to develop a rig configuration which will provide CFD validation data for the aerodynamics of a nacelle under representative windmilling conditions. Two flight regimes are considered, namely windmilling diversion and end-of-runway. CFD simulations of a 3D nacelle are used to determine primary aerodynamic mechanisms associated with boundary layer separation. Two rig configurations are developed and both 2D and 3D CFD analyses are used to achieve the design objectives. Overall, this work presents the design philosophy and methods that were pursued to develop a quasi-2D rig configuration representative of the aerodynamics of 3D-annular aero-engine nacelles under windmilling conditions.
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
Design optimisation of separate-jet exhausts with CFD in-the-loop and dimensionality reduction techniques
(AIAA, 2024-01-04) Hueso Rebassa, Josep; MacManus, David G.; Tejero, Fernando; Goulos, Ioannis; Abdessemed, Chawki; Sheaf, Christopher
For Ultra-High Bypass Ratio aero-engines, the exhaust system is likely to play a significant role on the aerodynamics and performance of the aircraft. For this reason, relatively rapid methods for the aerodynamic design and optimisation of exhaust systems are required to inform design decisions at early stages of the design process. Previous exhaust optimisation works encompassed Response Surface Model (RSM) based optimisations of nozzle configurations that were parametrised with a significant number of design variables. The RSM were constructed with a large database of designs that were assessed with fine computational meshes and well resolved boundary layers. However, the large number of design variables and the computational cost required to evaluate each exhaust design limited the optimisation capabilities. This work develops a relatively more rapid exhaust optimisation method based on CFD in-the-loop and dimensionality reduction. The methodology is based on coarse meshes and wall functions to guide the optimisation process and is coupled with methods for the identification of the dominant design variables. For an UHBR aero-engine exhaust design space of 16 design variables, it was found that the velocity coefficient could be characterised with only seven parameters. Based on these results, various optimisation methods were developed and applied. These targeted the maximisation of the velocity coefficient by optimising just the 7 dominant design variables. With these approaches, a similar benefit in exhaust performance relative to the baseline optimisation method was obtained approximately 4 times faster.
Open Access
Effects of aircraft integration on compact nacelle aerodynamics
(AIAA, 2020-01-05) Tejero, Fernando; Goulos, Ioannis; MacManus, David G.; Sheaf, Christopher
To reduce specific fuel consumption, it is expected that the next generation of aero-engines will operate with higher bypass-ratios, and therefore fan diameters, than current in-service architectures. These new propulsion systems will increase the nacelle size and incur in an additional overall weight and drag contribution to the aircraft. In addition, they will be installed more closely-coupled with the airframe, which may lead to an increase in adverse installation effects. As such, it is required to develop compact nacelles which will not counteract the benefits obtained from the new engine cycles. A comprehensive investigation of the effects of nacelle design on the overall aircraft aerodynamic performance is required for a better understanding on the effects of aero-engine integration. This paper presents a method for the multi-objective optimisation of drooped and scarfed non-axisymmetric nacelle aero-engines. It uses intuitive Class Shape Tranformations (iCSTs) for the aero-engine geometry definition, multi-point aerodynamic simulation, a near-field nacelle drag extraction method and the NSGA-II genetic algorithm. The process has been employed for the aerodynamic optimisation of a compact nacelle aero-engine as well as a conventional nacelle configuration. Subsequently, the designed architectures were installed on a conventional commercial transport aircraft and evaluated at different installation positions. A novel thrust-drag bookkeeping method has been used to evaluate different engine, nacelle and aircraft performance metrics. The main flow mechanisms that impact the installation effects on compact aero-engines configurations are identified. For the expected close-coupled installation position of future high bypass-ratio engines, the net vehicle force is increased by 0.44% with respect to a conventional architecture. The proposed method complements a set of enabling technologies that aim at the analysis, optimisation and evaluation of future civil aero-engines.