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Browsing School of Aerospace, Transport and Manufacturing (SATM) by Course name "PhD in Aerospace"
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Item Open Access Accidents caused by hazardous materials released in an urban environment: a numerical and experimental approach.(2019-04) Vasilopoulos, Konstantinos; Tsoutsanis, Panagiotis; Könözsy, László Z.This research studies the transport and dispersion of hazardous materials after a fire accident in an urban setting and the unpredictable threats provoked for the population and the environment. A fire accident may result, inter alia, from industrial activity or during the transportation of hazardous materials, such as diesel, petrol or kerosene liquids. In the current research, mineral oil pool fire accidents are examined in order to define the toxic smoke zones at different urban scale geometries. Three different urban scale geometries are examined: a) an isolated building, b) a street canyon and c) a staggered array of urban blocks. The fluid flow, the hazardous dispersion and the safety limits are studied using the Computational Fluid Dynamics (CFD) techniques and wind tunnel experiments. The Computational simulations were conducted using the CFD solver of Fluent and the Fire Dynamic Simulator (FDS). Both Reynolds-average Navier-Stokes (RANS) modes and Large Eddy Simulations (LES) methods were applied. Wind tunnel experiments were conducted in order to better understand the flow around these geometries and evaluate them with LES models. The numerical models were validated with wind tunnel experiments and with additional experimental data selected from the bibliography. The numerical results defined the toxic smoke limits and allowed the creation of simplified risk maps. The latter can define the mitigation measures after a fire accident.Item Open Access Aero-propulsive performance assessment approach to boundary layer ingestion aircraft(Cranfield University, 2023-04) Moirou, Nicolas G. M.; Laskaridis, Panagiotis; Sanders, Drewan S.A promising solution towards more sustainable and efficient aircraft propulsion relies upon the ingestion of the boundary layer flow that develops around the airframe. Amongst the plethora of concepts, the propulsive fuselage concept appears to be the most pragmatic configuration, as a direct adoption of conventional tube-and-wing aircraft, which has an additional propulsor integrated around its tail. Nonetheless, there is a lack of consensus in the quantification and interpretation of the performance of such vehicles. Long-established momentum-based bookkeeping schemes break down as their underlying assumptions do not hold true in highly-integrated airframe-propulsion systems. Alternative approaches have been brought forth by considering holistically the aircraft to evaluate its performance and decompose its aerodynamic forces. Notably, energy- and exergy-based approaches improve one’s understanding on the cause and effect of boundary layer ingestion mechanisms but require high computational demands with dense grids. In sought of a universal approach, energy- and momentum-based methods are used together in this work to quantify the coupled aerodynamic performance of boundary layer ingestion aircraft. The strengths of near-field momentum integrations are coupled with more informative energy-based flow assessments. The design space of a propulsive fuselage aircraft is explored via CFD after a reduction of its modelling to an axi-symmetric partial assembly of the fuselage and propulsor. With variations in the thruster position along the tail, its flow passage through the fan and pressure rise, and exhaust design, best performance is achieved with a concept where the propulsor lies at 90% of the fuselage chord, for a fan hub radius of 30% of the fuselage radius, that ingests around 43% of the boundary layer mass-flow, and applies a pressure rise of 1.29, to generate around a third of the total propulsive force requirement whilst savings 11% of fuel relative to a short-to-medium range aircraft propelled by state-of-the-art turbofans. The reasons for such savings are detailed with a first-of-its-kind fully energetic flow decomposition which aims at attributing boundary layer ingestion benefits to changes in propulsor design.Item Open Access Aeroacoustic simulation of rotorcraft propulsion systems.(Cranfield University, 2019-11) Vouros, Stavros; Pachidis, VassiliosRotorcraft constitute air vehicles with unique capabilities, including vertical take- off and landing, hover and forward/backward/lateral flight. The efficiency of rotorcraft operations is expected to improve rapidly, due to the incorporation of novel technologies into current designs. Moreover, enhanced or even new capabilities are anticipated after the introduction of advanced fast rotorcraft configurations into the future fleet. The forecast growth in rotorcraft operations is essentially associated with an expected increase in adverse environmental impact. With respect to the forthcoming rotorcraft aviation advancements, regulatory and advisory bodies, as well as communities, have focused their attention on reducing pollutant emissions and acoustic impact of rotorcraft activity. Consequently, robust and computationally efficient noise modelling approaches are deemed as prerequisites towards quantifying the acoustic impact of present and future rotorcraft activity. Ultimately, these approaches need to cater for unique operational conditions encompassed by modern rotorcraft across designated flight procedures. Additionally, individual variations of key design variables need to be resolved, in the context of design or operational optimisation, targeted at noise mitigation. This work elaborates on the development and application of a robust and computationally efficient methodology for the aeroacoustic simulation of rotorcraft propulsion systems. A series of fundamental modelling methods is developed for the prediction of helicopter rotor noise at fully-integrated operational level. An extensive validation is carried out against existing experimental data with respect to prediction of challenging aeroacoustic phenomena arising from complex aerodynamic interactions. The robustness of the deployed method is confirmed through a cost-effective uncertainty analysis method focused on aerodynamic sources of uncertainty. A set of generalised modelling guidelines is devised for the case of not available input parameters to calibrate the aerodynamic models. The aspect of multi-disciplinary optimisation of rotorcraft at aircraft level in terms of maximising the potential benefits of novel technologies is also tackled within this work. A holistic schedule of optimal active rotor morphing control is derived, offering simultaneous mitigation of pollutant emissions and acoustic impact across a wide range of the helicopter flight envelope. Finally, the developed noise prediction method is incorporated into an operational-level optimisation algorithm, demonstrating the potential of active rotor morphing with respect to reduction of ground-noise impact. The contribution to knowledge arising from the successful completion of this work comprises both the development of methodologies for helicopter aeroacoustic analysis and the derivation of guidelines and best practices for morphing rotor control. Specifically, a generic operational-level simulation approach is developed which effectively advances the state-of-the-art in mission noise prediction. New insight is provided with respect to the impact of wake aerodynamic modelling uncertainty on the robustness of noise predictions. Moreover, the aeroacoustic aspects of a novel morphing rotor concept are explored and quantifications with respect to the trade-off between environmental and noise disciplines are offered. Finally, a generalised set of optimal rotor control guidelines is derived towards achieving the challenging environmental goals set for a sustainable future rotorcraft aviation.Item Open Access Aerodynamic and cost modelling for aircraft in a multi-disciplinary design context.(Cranfield University, 2015-12) Di Pasquale, Davide; Savill, Mark A.; Kipouros, Timoleon; Holden, CarrenA challenge for the scientific community is to adapt to and exploit the trend towards greater multidisciplinary focus in research and technology. This work is concerned with multi-disciplinary design for whole aircraft configuration, including aero performance and financial considerations jointly for an aircraft program. A Multi-Disciplinary (MD) approach is required to increase the robustness of the preliminary design data and to realise the overall aircraft performance objectives within the required timescales. A pre-requisite for such an approach is the existence of efficient and fully integrated processes. For this purpose an automatic aero high-speed analysis framework has been developed and integrated using a commercial integration/building environment. Starting from the geometry input, it automatically generates aero data for loads in a timescale consistent with level requirement, which can afterwards be integrated into the overall multi-disciplinary process. A 3D Aero-solution chain has been implemented as a high-speed aerodynamic evaluation capability, and although there is not yet a complementary fully automated Aerodynamic design process, two integrated systems to perform multi-objective optimisation have been developed using different optimisation approaches. In addition to achieving good aircraft performance, reducing cost may be essential for manufacturer survival in today's competitive market. There is thus a strong need to understand the cost associated with different competing concepts and this could be addressed by incorporating cost estimation in the design process along with other analyses to achieve economic and efficient aircraft. For this reason a pre-existing cost model has been examined, tested, improved, and new features added. Afterwards, the cost suite has been integrated using an integration framework and automatically linked with external domains, providing a capability to take input from other domain tool sets. In this way the cost model could be implemented in a multi-disciplinary process allowing a trade-off between weight, aero performance and cost. Additionally, studies have been performed that link aerodynamic characteristics with cost figures and reinforce the importance of considering aerodynamic, structural and cost disciplines simultaneously. The proposed work therefore offers a strong basis for further development. The modularity of the aero optimisation framework already allows the application of such techniques to real engineering test cases, and, in future, could be combined with the 3D aero solution chain developed. In order to further reduce design wall-clock time the present multi- level parallelisation could also be deployed within a more rapid multi-fidelity approach. Finally the 3D aero-solution chain could be improved by directly incorporating a module to generate aero data for performance, and linking this to the cost suite informed by the same geometrical variables.Item Open Access Aeroelastic investigation of conventional fixed wings and bio-inspired flapping wings by analysis and experiment.(2018-09) Li, Hao; Guo, Shijun J.In this thesis, the structure and aeroelastic design, analysis and optimization of conventional fixed wing is firstly addressed. Based on the study results of conventional fixed wing, the study then focuses on the more complicated aerodynamics and aeroelasticity of flapping wing Micro Air Vehicles (MAV). A Finite Element (FE) model of a composite aircraft wing is firstly used as case study for the aeroelasticity of conventional fixed wing. A MATLAB-NASTRAN interfaced optimization platform is created to explore the optimal design of the wing. Optimizations using the developed platform show that 13% of weight reduction can be achieved when the optimization objective is set to minimize wing weight; and 18.5% of flutter speed increase can be achieved when aeroelastic tailoring of composite laminate layups is carried out. The study results further showed that the most sensitive part of the wing for aeroelastic tailoring is near the engine location, which contributes to the majority of flutter speed increment for optimization. In order to facilitate the structural design of non-circular cross section fuselage of Blended-Wing-Body (BWB) aircraft, an analytical model of 2D non-circular cross section is developed, which provides efficient design and optimization of the fuselage structure without referring to FE models. A case study based on a typical BWB fuselage using the developed model shows that by optimizing the fuselage structure, significant weight saving (17%) can be achieved. In comparison with the conventional fixed wing, insect flapping wings demonstrate more complicated aerodynamic and aeroelastic phenomena. A semi-empirical quasi-steady aerodynamic model is firstly developed to model the unsteady aerodynamic force of flapping wing. Based on this model, the aerodynamic efficiency of a Flapping Wing Rotor (FWR) MAV is investigated. The results show that the optimal wing kinematics of the FWR falls into a narrow range of design parameters governed by the dimensionless Strouhal number (St). Furthermore, the results show that the passive rotational of the FWR converges to an equilibrium state of high aerodynamic efficiency, which is a desirable feature for MAV applications. Next, the aerodynamic lift coefficient and efficiency of the FWR are calculated and compared with typical insect-like flapping wings and rotary wing. The results show that the aerodynamic efficiency of FWR in typical wing kinematics is higher than insect-like flapping wings, but slightly lower than the conventional rotary wing; the FWR aerodynamic lift coefficient (CL) surpassed the other wings significantly. Based on the numerical results, the study then continued to experimental investigations of the FWR. A prototype FWR model of weight 2.6g is mounted on a load cell to measure the instantaneous lift production. The kinematics of the wing is captured using high speed camera. Aeroelastic twist of the wing is measured using the resulting wing motion. Analyses by CFD and the quasi-steady aerodynamic model is then carried out and compared with experimental results. The study revealed that passive twist of the FWR wing due to aeroelastic effects forms desirable variations of wing Angle of Attack (AoA), which improves the aerodynamic performance of FWR. The results of the thesis provide guidance for structural, aerodynamic and aeroelastic design, analysis and optimization of conventional fixed wing, as well as bio-inspired flapping wing MAVs.Item Open Access Aircraft assembly process design for complex systems installation and test integration.(Cranfield University, 2019-04) Li, Tao; Lockett, Helen L.; Lawson, CraigThe assembly line planning process connects product design and manufacturing through translating design information to assembly integration sequence. The assembly integration sequence defines the aircraft system components installation and test precedence of an assembly process. From a systems engineering view point, this activity is part of the complex systems integration and verification process. At the early conceptual design phase of assembly line planning, the priority task of assembly process planning is to understand product complexities in terms of systems interactions, and generate the installation and test sequence to satisfy the designed system function and meet design requirements. This research proposes to define these interactions by using systems engineering concept based on traceable RFLP (Requirement, Functional, Logical and Physical) models and generate the assembly integration sequence through a structured approach. A new method based on systems engineering RFLP framework is proposed to generate aircraft installation and test sequence of complex systems. The proposed method integrates aircraft system functional and physical information in RFLP models and considers these associated models as new engineering data sources at the aircraft early development stage. RFLP modelling rules are created to allow requirements, functional, logical and physical modes be reused in assembly sequence planning. Two case studies are created to examine the method. Semi- structured interviews are used for research validation. The results show that the proposed method can produce a feasible assembly integration sequence with requirements traceability, which ensures consistency between design requirements and assembly sequences.Item Open Access Analysis of the effect of impact damage on the repairability of CFRP composite laminates.(2017-02) Alzeanidi, Nasser; Ghasemnejad, HessamPolymer composite materials are common in the aerospace application such as aircraft structures including primary and secondary structures. Therefore, there has been an increasing demand for composites in both the military and civilian aircraft industry. At least 50% of the next generation of military and civil aircraft structures are likely to be made from composites. The most important properties for composite materials in aircraft application was the high strength-to-weight ratios, stiffness-to-weight ratios and easy to repair. However, the composite materials have low resistance for impact damage. Impact can lead to significant strength reduction in aircraft structure about 40% to 60% of an undamaged composite laminate strength. Therefore, establish a numerical methodology to defined the optimum repair joint to restore sufficient strength of damaged aircraft composite structures during some operations and exercise activities with limited resources which will be the main contributions to knowledge in this thesis. To achieve this contribution need to understanding of the behaviour of Carbon Fibre Reinforced Plastic (CFRP) composite laminates subject to high velocity impact and the unrepaired composite laminates and repaired (stepped joint) subject to compression after impact test. Therefore, this study consists of two parts:- first, part a combined of numerical simulation and experimental investigation have been used to evaluate the woven CFRP laminate subject high velocity impact. The selected impact velocities were (140m/s, 183m/s, 200m/s, 225m/s, 226m/s, 236m/s, 270m/s, 305m/s, 354m/s and 368m/s) in order to evaluate the induced impact damage in three different thickness of CFRP composite laminates (6 mm, 4.125 mm and 2.625 mm) these velocities were selected according the gas gun limitation. The woven composite laminate made of Hexcel G0926 Carbon Fabric 5 harness 6K, Areal Weight 370 gsm. The resin used was Hexcel RTM 6, cured for 1 hour 40 minutes at 180° C at a pressure of 100 psi, with an average thickness of 0.375mm. The laminates were comprised of 16 layers, using the following stacking sequence: [(0/90); (±45); (±45); (0/90); (±45); (±45); (0/90); (0/90); (±45); (0/90); (±45); (0/90); (±45); (0/90); (±450); (0/90)], 11 layers, using the following stacking sequence: 0/90; ± 45; 0/90; ± 45; 0/90; ±45; 0/90; ± 45; 0/90; ±45; 0/90 and 7 layers, using the following stacking sequence: ± 45; 0/90; 0/90; ±45; 0/90; 0/90; ±45. The density of woven CFRP laminates was 1.512e-3 ±1e-6 grm/mmÖ³. The penetration process and also change of kinetic energy absorption characteristics have been used to validate the finite element results. The experimental and numerical method in this study show a significant damage occurs, including delamination, compression through thickness failure, out-of-plane shear failure and in-plane tensile failure of the fibres located at the rear surface when the projectile penetrates the laminate. The penetration mechanism of the projectile had a “plugging-type” (shear) failure and the hole that was formed after impact was conical in shape were shown in experimental and also verified in the numerical model. The residual kinetic energy in numerical model is 5.0 % larger than experimental data which is significantly matched in all simulated cases. In part two a finite element model is established to optimise the repair joint to restore sufficient strength of damaged composite laminate and used compression after impact test to compare the compression failure load of the sample. In order to achieve this an optimised repair models of stepped lap joints with variable parameters such as number of steps and length of steps have been experiment the undamaged composite laminate and composite laminate subject to high velocity impact and also created a numerical model for these experimental. The experimental CAI failure load of undamaged 7 Plies CFRP composite laminate higher than the failure load of damaged specimens by approximately 23%. The undamaged 11 Plies CFRP composite laminate failed at approximately 40% higher than the damaged specimens. Moreover, the difference between the experimental and numerical results of above tests was about 10%. The numerical model of repaired composite laminate show the damage initiated at the end of overlap and the average compression failure load of the stepped lap joint increased with the increasing of the number of step and length of step. The 85% and 90% of compressive failure load has been restored.Item Embargo Application of CFD zooming for preliminary design of a low emissions combustor.(2018-10) Sun, Xiaoxiao; Sethi, Vishal; Li, YiguangThe design of low emissions combustors is particularly challenging as there is a requirement to deliver designs that meet a large number of performance, emissions and operability (often conflicting) objectives. There is an increasing need for combustor preliminary design and performance tools which can be used in the early phases of the design process for rapid design space exploration thereby reducing the risk and cost in the long term. Although both reduced order models and higher fidelity tools have been widely used for preliminary design independently, significant benefit can be derived from using a multi-fidelity modelling approach to address the limitation of reduced order model (accuracy) and high fidelity CFD (time and cost). To the author’s best knowledge there is no information in the public domain related to the coupling of reduced order models with higher fidelity 3D CFD multi-fidelity modelling tools for low emissions gas turbine combustion systems. Such a tool has a potential to offer a good compromise between modelling accuracy and computational expense. In this PhD research, a novel multi-fidelity zooming combustor preliminary design method is proposed. The method uses design outcomes of an existing reduced order model based design tool to construct CFD models for a series of RANS simulations. A case study for the design of a Lean Direct Injection Partially Premixed combustor was conducted to identify the limitations of an existing reduced order modelling approach. Dedicated CFD simulations were performed to demonstrate that improved methods/models/correlations can be derived from these higher fidelity simulations to refine the existing reduced order model. The main research contributions are summarised below: External aerodynamics – Performance is sensitive to inlet velocity profiles, the effect of which cannot be reflected in ROMs, realistic compressor outlet profiles is needed instead of generic turbulent pipe flow profiles. – Performance maps were generated from CFD which include more degrees of freedom and suggest a different ‘optimum locus’ than 1D correlations. Fuel injector initial conditions – The Sauter Mean Diameter calculated from correlations in the ROM is not suitable to be used as injection initial condition. Detailed correlations on jet breakup were used to generate representative droplet size and velocity for different nozzle designs and conditions. – Swirler flow split correlations does not account for flow turning in the venturi and the pre-mixer, coarse mesh CFD was sufficient to generate more accurate flow splits among different stages. Reacting flow – The initial 10 fuel nozzle ports design from the ROM was not sufficient for good mixing quality at the main stage, which resulted in higher flame temperature. The number was increased to 16, which provides more uniform flame distribution at the circumferential direction. – Three of the four methods used to generate the time delay provides consistent results. The time delay was used as an input of the ROM thermoacoustic analysis model. – The reactor layout can be better customised for emissions prediction with extra zones within the pilot injector and the dilution zone to account for reaction and recirculation. – Combustor cooling design was refined without modifying the variables of ROM, in which circumferential distribution was not captured. Simplified re-fining method was developed at less computational expense compared to complete Conjugate Heat Transfer simulations with the radiation model. Based on these findings, the reduced order design tool could be refined once the data from all parametric study cases are extracted and incorporated in the model, which is recommended as the future development of the work. The CFD model constructed could also be used to initiate higher fidelity Large Eddy Simulation.Item Open Access Application of compressor water injection for the reduction of civil aircraft NOᵪ emissions.(2018-12) Block Novelo, David Alejandro; Igie, Uyioghosa; Nalianda, DevaiahGas turbine Nitrogen Oxide (NOx) emissions are directly proportional to combustion temperature. These contaminants are associated with respiratory diseases and damage to the local water quality and wildlife. Higher demand on civil aviation, coupled to high-pressure ratio (and thus, temperature-ratio) engines, have caused aviation-borne NOᵪ Gas turbine Nitrogen Oxide (NOx) emissions are directly proportional to combustion temperature. These contaminants are associated with respiratory diseases and damage to the local water quality and wildlife. Higher demand on civil aviation, coupled to high-pressure ratio (and thus, temperature-ratio) engines, have caused aviation-borne NOᵪ emissions to double since 1990. This is of concern around airports, at operations below 3,000 ft. where the concentration of air traffic is high and the population faces direct exposure to engine contaminants. This thesis explores the use of atomized water droplets into an engine compressor as a way of intercooling the cycle and in doing so reducing NOᵪ emissions. The use of water injection is proposed to be applied only during take-off and climb up to 3,000 ft. The analysis of water injection is firstly applied to common turbofan architectures (2 and 3-spool), under varied ambient conditions. The gas turbines are simulated by means of an in-house performance simulating tool, Turbomatch. The changes in cycle temperature when water injection is applied, are accounted for by means of a stand-alone analytical compressor model. The platform calculates the thermodynamic exchange between the gas path of the engine and the water droplets in the Lagrangian frame of reference. The engine models are then integrated into an in-house aircraft performance simulating tool, Hermes. Two types of aircraft, narrow and wide-body, are considered for operations with the water injection system. The performance benefits noted in the stand-alone engine section, are evaluated considering the extra system weight for different missions ranging from 500 to 11,000 km. The observed theoretical trends are then confirmed by means of an experiment performed on a stationary gas turbine. The test includes performance monitoring (pressures, temperatures, mass flows), water droplet measurements, and exhaust emissions analysis. The most optimistic case of water injection shows a reduction of NOx emissions greater than 50%, for the period when water is used. This technology, when applied after the fan compressor, is effective at ambient temperatures as low as 5°C and is more promising in 3-spool engines. For the shortest mission considered, equivalent to a journey from London to Paris, the aircraft benefits from a small fuel saving, despite of the extra weight. For longer missions, there is a negligible fuel penalty (0.05%) derived from the extra payload. In all the cases Landing and Take-Off (LTO) emissions are estimated to be reduced by 42-43%. A reduction of NOx emissions of 25% is achieved experimentally when injecting 2% water-to-air ratio. The study concludes that compressor water injection is a feasible solution that can significantly reduce the environmental footprint of aviation emissions to double since 1990. This is of concern around airports, at operations below 3,000 ft. where the concentration of air traffic is high and the population faces direct exposure to engine contaminants. This thesis explores the use of atomized water droplets into an engine compressor as a way of intercooling the cycle and in doing so reducing NOᵪ emissions. The use of water injection is proposed to be applied only during take-off and climb up to 3,000 ft. The analysis of water injection is firstly applied to common turbofan architectures (2 and 3-spool), under varied ambient conditions. The gas turbines are simulated by means of an in-house performance simulating tool, Turbomatch. The changes in cycle temperature when water injection is applied, are accounted for by means of a stand-alone analytical compressor model. The platform calculates the thermodynamic exchange between the gas path of the engine and the water droplets in the Lagrangian frame of reference. The engine models are then integrated into an in-house aircraft performance simulating tool, Hermes. Two types of aircraft, narrow and wide-body, are considered for operations with the water injection system. The performance benefits noted in the stand-alone engine section, are evaluated considering the extra system weight for different missions ranging from 500 to 11,000 km. The observed theoretical trends are then confirmed by means of an experiment performed on a stationary gas turbine. The test includes performance monitoring (pressures, temperatures, mass flows), water droplet measurements, and exhaust emissions analysis. The most optimistic case of water injection shows a reduction of NOᵪ emissions greater than 50%, for the period when water is used. This technology, when applied after the fan compressor, is effective at ambient temperatures as low as 5°C and is more promising in 3-spool engines. For the shortest mission considered, equivalent to a journey from London to Paris, the aircraft benefits from a small fuel saving, despite of the extra weight. For longer missions, there is a negligible fuel penalty (0.05%) derived from the extra payload. In all the cases Landing and Take-Off (LTO) emissions are estimated to be reduced by 42-43%. A reduction of NOx emissions of 25% is achieved experimentally when injecting 2% water-to-air ratio. The study concludes that compressor water injection is a feasible solution that can significantly reduce the environmental footprint of aviation.Item Open Access Assumption management in model-based systems engineering: an aircraft design perspective.(2021-12) El Fassi, Soufiane; Riaz, Atif; Guenov, Marin D.Early design of complex systems is characterised by significant uncertainty due to lack of knowledge, which can impede the design process. In order to proceed with the latter, assumptions are typically introduced to fill knowledge gaps. However, the uncertainty inherent in the assumptions constitutes a risk to be mitigated. In fact, assumptions can negatively impact the system if they turn out to be invalid, such as causing system failure, violation of requirements, or budget and schedule overruns. Within this context, the aim of this research was to develop a computational approach to support assumption management in model-based systems engineering, with an explicit consideration of the uncertainty in assumptions. To achieve the research aim, the objectives were to: (1) devise methods to enable assumption management in a model-based design environment; and (2) devise methods to manage risk of change due to invalid assumptions, with an explicit consideration of both assumptions and margins. The scope was limited to the early stages of aircraft design. To evaluate this research, a demonstration was performed based on two use cases to assess whether the methods work as intended. The developed methods were demonstrated to industry experts in order to obtain feedback on expected usefulness in practice, thus assessing the impact of this research. The experts concluded that the proposed methods are innovative, useful and relevant to industry, where these methods can lead to: (i) fewer undesired iterations, due to earlier identification and management of risks associated with assumptions; and (ii) a better margin balance, due to timely and interactive margin revision. Future work includes further industrial evaluation, extending the research scope and studying the scalability and associated costs of the proposed methods.Item Open Access Boundary layer ingestion performance assessments with application to business jets.(2018-07) Sanders, Drewan S.; Laskaridis, PanagiotisAdvancements in propulsion system performance are reliant on improvements in propulsive efficiency, through increases in turbofan bypass ratio. This requires larger nacelle diameters, which incur external aerodynamic penalties. Business jets cruise at high subsonic Mach numbers, and are therefore normally propelled by high specific thrust turbofans. The business jet may benefit from a BLI propulsion system, whereby the specific thrust may be reduced without incurring such heavy penalties in external drag rise. The aim of the research is to perform a design exploration study on BLI applied to a business jet, with emphasis on external aerodynamics. Methods are developed to thoroughly analyse aerodynamic coupling between propulsor and airframe. A multi-physics, control-volume based approach led to the development of near-field momentum-based, far-field momentum-based and energy-based net-vehicle-force formulations. The former two, allowed for a set of thrust-force accounting systems to be defined. Energy-based methods, allowed for flow-field decompositions into different physical mechanisms. These include flow phenomena internal and external to the jet plume. The practical implications associated with applying these methods to RANS CFD solutions, is examined. This hinges around viscous stress tensor field continuity in the flow domain. It was found that the k — w SST turbulence model, along with a Green-Gauss Cell-Based gradient scheme, produced a continuous viscous stress tensor field. Having resolved this, the assessment methods were applied to solutions of non-propelled and propelled bodies. These methods were applied to control volumes having varying extents, which showed the far-field momentum-based method to be sensitive to spurious affects. The energy-based formulation, on the other hand, was observed to be relatively insensitive spurious affects. Good agreement (within 4%) was found between the forces predicted by all three methods over a non-propelled body. A very close agreement was observed between far-field momentum-based and energy-based results (within 1%) over the propelled body. However, much larger discrepancies were observed when compared against the near-field results. This was attributed to the increase in flow-field complexity, which now contained BL, shock and jet interaction regions. A design exploration study was performed by retrofitting a business jet with a fuselage concentric propulsor, powered by the baseline podded engines. A preliminary parametric study was first performed to gauge conditions favourable to BLI benefit. A ram drag approach to modelling BLI benefit was based on a flat plate analogy to obtain boundary layer profiles. Thrust-split, BLR, fan efficiency and intake pressure recoveries, were varied parametrically to asses potential benefits. An optimum SFC benefit between 5-7.5% was achieved at thrustsplits between 30-35%, when ingesting 65-90% of the BL thickness. This guided the the parametric CFD studies, where two tail-cone positions were examined. The first was placed at the top of the tail-cone, and the second positioned midway along the tail-cone. Benefits were only realised for the latter, where a 3-4% improvement in SFC was realised for a thrust-split around 20%, by ingesting 40% of the BL thickness. Energy breakdowns and decompositions were performed on all of the cases. One of the significant outcomes of this research was revealing that a significant proportion of the thrust force may be attributed to the isentropic expansion region within the jet plume's core.Item Open Access Building safety into the conceptual design of complex systems. An aircraft systems perspective.(2021-06) Jimeno Altelarrea, Sergio; Guenov, Marin D.; Riaz, AtifSafety is a critical consideration during the design of an aircraft, as it constrains how primary functions of the system can be achieved. It is essential to include safety considerations from early design stages to avoid low-performance solutions or high costs associated with the substantial redesign that is commonly required when the system is found not to be safe at late stages of the design. Additionally, safety is a crucial element in the certification process of aircraft, which requires compliance with safety requirements to be demonstrated. Existing methods for safety assessment are limited in their ability to inform architectural decisions from early design stages. Current techniques often require large amounts of manual work and are not well integrated with other system engineering tools, which translates into increased time to synthesise and analyse architectures, thus reducing the number of alternative architectures that can be studied. This lack of timely safety assessment also results in a situation where safety models evolve at a different pace and become outdated with respect to the architecture definition, which limits their ability to provide valuable feedback. Within this context, the aim is to improve the efficiency and effectiveness of design for safety as an integral part of the systems architecting process. Three objectives are proposed to achieve the stated aim: automate and integrate the hazard assessment process with the systems architecting process; facilitate the interactive introduction of safety principles; and enable a faster assessment of safety and performance of architectures. The scope is restricted to the earlier (conceptual) design stages, the use of model-based systems engineering for systems architecting (RFLP paradigm) and steady-state models for rapid analysis. Regarding the first objective, an enabler to support the generation of safety requirements through hazard assessment was created. The enabler integrates the RFLP architecting process with the System-Theoretic Process Analysis to ensure consistency of the safety assessment and derived safety requirements more efficiently. Concerning the second objective, interactive enablers were developed to support the designer when synthesizing architectures featuring a combination of safety principles such as physical redundancy, functional redundancy, and containment. To ensure consistency and reduce the required amount of work for adding safety, these methods leverage the ability to trace dependencies within the logical view and between the RFLP domains of the architecture. As required by the third objective, methods were developed to automate substantial parts of the creation process of analysis models. In particular, the methods enable rapid obtention of models for Fault Tree Analysis and subsystem sizing considering advanced contextual information such as mission, environment, and system configurations. To evaluate this research, the methods were implemented into AirCADia Architect, an object-oriented architecting tool. The methods were verified and evaluated through their applications to two aircraft-related use cases. The first use case involves the wheel brake systems and the second one involves several subsystems. The results of this study were presented to a group of design specialists from a major airframe manufacturer for evaluation. The experts concluded that the proposed framework allows architects to define and analyse safe architectures faster, thus enabling a more effective and efficient design space exploration during conceptual design.Item Open Access Component-driven computational design of complex engineering systems.(2018-08) Bile, Yogesh Hanumant; Guenov, Marin D.; Molina-Cristobal, ArturoDuring the conceptual design of complex systems, architects study a number of different options, which comprise the architectural design space. Usually, new system architectures (SAs) are created by modifying existing ones, e.g., by deleting existing and/or adding new elements. Once the concept is synthesised, the architect wishes to swiftly find the effect of the proposed architectural changes at system level. This would involve sizing of the modified sub-systems, and then, obtaining the system level performance. In turn, this involves time-consuming activities, such as re-arrangement (orchestration) of computational tasks and models. Also, depending on the results, the architect may undertake further modifications. When doing this, a means to navigate across the RFLP (Requirements-Functional-Logical-Physical) views of the SA may be required, in order to trace elements affected by these modifications. Generally, several iterations are involved between architecting and sizing during conceptual design, which, if manually performed, result in a tedious and time-consuming process. There are existing methods which address this problem, but these have significant limitations in that they are usually system specific and often involve an excessive amount of time-consuming manual tasks. Within this context, the research aim is to improve the efficiency of the architectural design space exploration (ADSE) process, by automating repetitive computational tasks, thus enabling the designer to swiftly and interactively explore multiple SA options. A novel method, comprised of two parts, has been developed to achieve the aim. In the first part, a graph-theoretic approach is employed to enable architectural element dependency analysis. Here, the relationships between the architectural elements are stored as a graph. Algorithms, such as ‘Depth First Search’ and ‘Transitive Closure’ are then applied to assist the architect in tracing the dependencies between elements that might be affected by a proposed change to other elements of the SA. In the second part, the architecture is assessed to find the system level performance. The inputs needed for rapid assessment include the functional and logical views of the SA, and the requisite steady-state computational models associated with each of the ‘logical’ components. The assessment process itself consists of three steps. In the first step, the sequence of the sub-systems is automatically generated by extracting a sub-systems source-sink ‘Dependency Structure Matrix (DSM)’ from the logical view, followed by the application of an algorithm which determines the systems’ sizing sequence. In the second step, the individual sub-systems and system level workflows are constructed. Here, the computational workflow (a network of computational models) is represented as a bipartite graph. A maximum matching enumeration algorithm is used to find all possible workflows for a given model set, and another algorithm, to choose from these the most computationally efficient one, i.e., the workflow with the lowest number of reversed variables. In the third step, the workflows produced in the second step and subsystems ’sizing sequence obtained in the first step are combined to produce a complete workflow. To demonstrate and evaluate the proposed enablers, the author developed a prototype object-oriented architecting tool. The enablers were individually and collectively verified on representative test-cases. Comparison with the existing methods confirmed the claimed advantages of the proposed approach, namely, reducing the number of manual activities, which results in swifter and interactive ADSE process. Feedback obtained from experts in the aircraft industry during an initial qualitative evaluation session confirmed the usefulness of the proposed method.Item Open Access Computational techniques for aircraft evolvability exploration during conceptual design.(2018-02) Van Heerden, Albert Stevan Johan; Guenov, Marin D.; Molina-Cristobal, ArturoEvolvability is a critical consideration during the design of an aircraft. It refers to the extent to which a baseline design could be reused, or `easily' modified to create descendant designs that would meet future requirements. Since a major fraction of the cost of an aircraft programme is determined by decisions made during conceptual design, it is essential that the design space is explored thoroughly during this stage to find evolvable designs. Existing computational methods to perform such exploration exist, but are limited in two respects. The first of these is that, with existing techniques, derivatives are usually generated by applying pre-specified modifications to a selected baseline, such that each derivative in a study is only linked to a single baseline. The designer must therefore evaluate large numbers of baseline-derivative pairs to adequately capture the evolution options available. The second limitation concerns an absence of appropriate down-selection criteria to narrow down the number of design points when evolvability is considered. The work presented in this thesis addresses these limitations. The aim was to develop computational techniques that would enable aircraft designers to explore the evolvability of their designs more efficiently and effectively during the conceptual design stage. The scope was limited to civil transport aircraft and specifically to airframes. The work is applicable to both single- and twin-aisle aircraft, but the focus was, to a small degree, more on single-aisles. The research resulted in two main contributions: 1) a framework to provide a means to link all derivatives to all the baselines; and 2) a set of techniques to filter out inferior designs systematically. The framework builds on the premise that the degree of `similarity' between two ,designs could be used as an estimate for the redesign e ort (i.e. resource expenditure) required to change one of these into the other. Case studies involving existing aircraft families were conducted to determine which design changes could be considered `reasonable'. Based on this information, a set of techniques to assess airframe similarity was developed, which involves automatically predicting possible commonality across two designs. Several algorithms were devised to achieve this, including one that solves a longest common subsequence problem to find common body segments and a simple optimisation procedure to find common wing elements. Notably, these techniques can be used to compare aircraft with dissimilar configurations. For testing purposes, the framework was applied to several existing and future aircraft. The results showed that the predicted commonality matches published information regarding commonality and design re-use between designs. The framework essentially removes the need to model each future design option based on a specific starting design. The design filtering techniques involve the application of set-based design to facilitate systematic down-selection of potential designs. Specifically, it is demonstrated how established set-based design criteria could be adapted to prune an evolvability design space progressively. To demonstrate the usefulness of the research, it was applied to an example, concerning design candidates for a new single-aisle, environmentally friendly passenger aircraft. The results of this study were presented to a panel of design specialists from Airbus UK. The panel concluded that the proposed similarity assessment provides reasonable initial estimates for redesign e ort and that the overall approach adds value to the evolvability exploration process.Item Open Access Conceptual design and assessment of turboelectric and hybrid electric propulsion system architectures for civil transport aircraft.(2018-03) Tashie-Lewis, Bernard Chukwudi; Laskaridis, Panagiotis; Miller, Paul; Husband, PaulTo achieve ambitious future environmental targets for aircraft set out by organisations such as NASA and the European Union, turboelectric distributed propulsion (TeDP) has been proposed as a novel concept that has the potential to achieve these targets by significantly improving integrated propulsion-airframe performance. Realising TeDP as a technology option brings into play a number of design and development challenges due to the highly integrated natured of TeDP-airframe configurations, low technology-readiness-levels of key enabling technologies and new modes of operation opened up by shift to a more electric architecture. In tackling these challenges a multidisciplinary and integrated method to assess the benefits and challenges of turboelectric and hybrid-electric propulsion system configurations by considering the effect of aircraft size, mission specifications, airframe, electrical system, energy storage, propulsor architecture and gas turbine architecture was created. The method created was used in the assessment of turboelectric and hybrid electric performance for a regional transport aircraft and a medium haul transport aircraft. For the regional role the employment of a DC hybrid superconducting turboelectric architecture managed to achieve 16.7% block fuel saving and 3.23% total energy consumption saving over a baseline turboprop aircraft at 600 n.mi range. Driving performance benefits was increased duration of mission time batteries spend discharging at relatively high battery power rating which overcomes weight penalties from installation of electric machinery. For medium haul role the employment of a geared hybrid electric architecture managed to achieve a 3.07% block fuel saving over a baseline turbofan aircraft at 900 n.mi range. Driving performance benefit for the mission was increased battery-operative-cruise time at relatively high battery power rating overcoming aircraft weight penalty and electric machinery installation weight penalty. Despite fuel burn reduction, hybrid electric aircraft consumes more energy than a baseline configuration primarily due to utilisation of additional energy from battery pack.Item Metadata only Conceptual design methodologies appropriate to supersonic business jets(2018-11) Sun, Yicheng; Smith, Howard; Fielding, JohnThis project aims to study the status of the issues related to Supersonic Business Jet (SSBJ) conceptual design, to develop design methodologies appropriate to SSBJs, and to explore the design space of low-boom low-drag supersonic transport concepts. The design model appropriate to SSBJs is developed in the Cranfield multidisciplinary design analysis and optimization environment – GENUS. The mass breakdown, engine model, aerodynamic analysis, stability and control, and sonic boom prediction methods are developed in the GENUS framework. Optimizers help to explore the design space based on the model. Through the research, the current supersonic transport concepts are analysed and the supersonic natural laminar flow wing concept is found to leave little space for sonic boom mitigation. The most significant finding is the low-boom solution through the geometry shaping to the volume and lift effects. The low-drag requirement is not necessarily contradicted by the low-boom requirement. The low-boom optimization achieves a sonic boom reduction from 2.6 psf to 0.6 psf and the L/D increase from 8.96 to 10.67. The low-drag optimization achieves a L/D increase from 8.96 to 10.81 and sonic boom reduction from 2.6 psf to 1.0 psf. A low-boom low-drag SSBJ and a low-boom low-drag supersonic airliner concepts are designed in a multidisciplinary view. Pdf available on request and Howard Smith's permission.Item Open Access Conceptual design synthesis and multidisciplinary optimisation of unmanned combat aerial vehicles.(2019-12) Sepulveda Palacios, Eduardo; Smith, Howard; Fielding, JohnThe purpose of this research is to investigate and develop conceptual design methodologies and computational tools appropriate to the design and analysis of low-observable Unmanned Combat Aerial Vehicles (UCAVs), performing a wide variety of missions, with various payload and performance requirements, as well as a wide range of operational constraints, from subsonic to high supersonic flight regimes. Undoubtedly, unmanned aircraft have transformed many aspects of aeronautics and aviation, with military applications often leading these transformational efforts. UCAVs have emerged as a potential strategy to counter technological, operational, and economical challenges to the future of aerial warfare. These challenges include an aging fleet of 4th generation fighters, the deployment of new, advanced 4+ and 5th generation platforms, the reported high vulnerability of current unmanned aerial vehicles, as well as the future development of hypersonic vehicles and weapons. In order to investigate future aircraft configurations, the GENUS aircraft design environment was envisioned by Prof. Howard Smith at Cranfield University’s Aircraft Design Group in 2012. This framework relies on a central architecture with high degrees of modularity and flexibility capable of designing, analysing, and optimising several species of aircraft with similar analysis tools, revealing the real differences and potential advantages of new designs. Mass estimation, propulsion, aerodynamics, performance, radar cross section estimation, and aero-thermal analysis tools have been integrated into the GENUS framework in order to investigate the design space of UCAVs. Validation of these methods has been hampered due to the often restricted access to quality data of UCAVs and similar configurations against which to compare and from which to generate higher fidelity models. Specific steps for improving the accuracy of the methods in the future have been identified and proposed in §9.2. Design space explorations performed in this research include a mission parameter trade study for subsonic UCAVs in Hi-Lo-Hi missions, the conceptual and preliminary design of a UCAV platform with performance matching that of current 5th generation fighters, a fully supersonic deep-interdiction mission trade study, and a high-supersonic (M ≥ 3.0) carrier-based UCAV for time-critical strike missions.Item Open Access A concurrent engineering framework to explore the servicer-client relationship in on-orbit servicing.(2018-12) Matos De Carvalho, Tiago; Kingston, Jennifer; Hobbs, Stephen E.The implementation of On-Orbit Servicing (OOS) in the development and operation of space systems has been pursued to enable inspection, maintenance, repair and assembly of systems in space. Performing such tasks robotically involves the consideration of two sides, a Servicer satellite performing the necessary tasks and a Client satellite receiving it. A critical point for a realistic consideration of OOS demands the concurrent approach of both sides. Despite the current interests towards OOS, there is still a gap in the research into the relationship of Client and Servicer. This research aims to develop and demonstrate a methodology to technically incorporate On-Orbit Servicing, at a system-level, to the mission design process and operation of current and new satellites. The first objective deals with the systematic arrangement of the current available knowledge. A top-down approach is used to provide a taxonomy of servicing, followed by the functional decomposition of the main tasks. This objective clarifies the main issues observed today in OOS, directly related to the Client-Servicer relationship. The second objective is to establish the proposed framework. Agent Based Modelling and Simulation is used to implement the main guidelines and concept of operation, and to output different metrics to allow users (Servicers and/or Clients) to evaluate the attractiveness of various OOS scenarios. The mathematical background for the different metrics is defined and discussed. This is complemented by a solution exploration feature for specific types of OOS. A set of cases is presented based on current interests of operators, providing coverage of potential scenarios to use the framework. The proposed objectives are met, achieving the main research aim. The results help to illustrate the effects of servicing in the systems design and operation. Features of the framework expand the capacity to identify potentially attractive conditions for both sides. Such characteristics are not observed in the current published research and represent a powerful tool to be employed at early stages of design and procurement.Item Open Access Contrail-free aero-engines.(2016-08) Qureshi, Sarah; Pilidis, PericlesThis thesis presents a contrail-free aero-engine designed to reduce the aviation induced global warming through the development of a condensation and containment mechanism for the exhaust water vapour content of an aero-engine. This mechanism intends to eliminate the source of contrail formation. A pressure-based turbomachinery defined as the water expeller is developed and introduced as a modular attachment to a standard aero-engine. It employs the use of centrifugal compression to generate pressure in the exhaust gas leading to a phase change that precipitates out the water content of the core exhaust gases. The water produced is drained out of the device and collected within the engine. The heat dissipated by water during condensation is absorbed by the remaining combustion gases. The design of the centrifugal water expeller is derived from a patented invention and evolved into a practical system. The theory of centrifugal extraction is explained and the underlying physics is established. This proceeds with a thermodynamic analysis whereby data for mechanical design is computed and advanced towards a prototype ready engineering model inclusive of structural design and structural analysis. The power requirements of this system are determined using thermodynamic data. In the preliminary design, the inclusion of the water expelling device results in a thirty percent increase in the length of the engine which has a likelihood of being reduced through optimization. The initial design parameters of the system are obtained from the performance analysis of a standard high-bypass three-spool turbofan engine and the study of atmospheric science and water physics. The design of the condensation device is validated through the study of the thermo-chemistry of the exhaust gases and a simple heat transfer analysis. The inter-gaseous exchange of energy at the molecular level during the process of condensation is also quantified. The performance of the standard engine with the integration of the centrifugal water expeller is analysed and progressed towards the performance evaluation of a standard wide body large aircraft with four contrail-free engines on board. Initial estimates indicate an increase in the weight of the engine by twenty five percent with the installation of the centrifugal water expeller onto the engines. This is merely a two percent increase in the overall weight of the aircraft. The integration of the mechanical device with the aero-engine results in an environmentally favourable engine-aircraft configuration with a three percent thrust penalty which is recognized as the acceptable trade-off for environmental benefits.Item Open Access Cooperative control of multi-uavs under communication constraints.(2018-10) Lee, Hae-In; Shin, Hyo-Sang; Tsourdos, AntoniosThis research aims to develop an analysis and control methodology for the multiple un-manned aerial vehicles (UAVs), connected over a communication network. The wireless communication network between the UAVs is vulnerable to errors and time delays, which may lead to performance degradation or even instability. Analysis on the effects of the potential communication constraints in the multiple UAV control is a critical issue for successful operation of multiple UAVs. Therefore, this thesis proposes a systematic method by incorporating three steps: proposing the analysis method and metrics considering the wireless communication dynamics, designing the structure of the cooperative controller for UAVs, and applying the analysis method to the proposed control in representative applications. For simplicity and general insights on the effect of communication topology, a net-worked system is first analysed without considering the agent or communication dynamics. The network theory specifies important characteristics such as robustness, effectiveness, and synchronisability with respect to the network topology. This research not only reveals the trade-off relationship among the network properties, but also proposes a multi-objective optimisation (MOO) method to find the optimal network topology considering these trade-offs. Extending the analysis to the networked control system with agent and communication dynamics, the effect of the network topology with respect to system dynamics and time delays should be considered. To this end, the effect of communication dynamics is then analysed in the perspective of robustness and performance of the controller. The key philosophy behind this analysis is to approximate the networked control system as a transfer function, and to apply the concepts such as stability margin and sensitivity function in the control theory. Through the analysis, it is shown that the information sharing between the agents to determine their control input deteriorates the robustness of their stability against system uncertainties. In order to compensate the robustness and cancel out the effect of uncertainties, this thesis also develops two different adaptive control methods. The proposed adaptive control methods in this research aim to cope with unmatched uncertainty and time-varying parameter uncertainty, respectively. The effect of unmatched uncertainty is reduced on the nominal performance of the controller, using the parameter-robust linear quadratic Gaussian method and adaptive term. On the other hand, time-varying parameter uncertainty is estimated without requiring the persistent excitation using concurrent learning with the directional forgetting algorithm. The stability of the tracking and parameter estimation error is proved using Lyapunov analysis. The proposed analysis method and control design are demonstrated in two application examples of a formation control problem without any physical interconnection between the agents, and an interconnected slung-load transportation system. The performance of the proposed controllers and the effect of topology and delay on the system performance are evaluated either analytically or numerically.