In this globalised world where the efficient transportation of people and goodsgreatly contributes to the development of a given region or country, the aviationindustry has found the ideal conditions for its development, thereby becoming in one ofthe fastest growing economic sectors during the last decades. The continuing growth inair traffic and the increasing public awareness about the anthropogenic contribution toglobal warming have meant that environmental issues associated with aircraftoperations are currently one of the most critical aspects of commercial aviation. Severalalternatives for reducing the environmental impact of aircraft operations have beenproposed over the years, and they broadly comprise reductions in the number of aircraftoperations, changes in the type of aircraft, and changes in the aircraft operational rulesand procedures. However, since the passenger traffic is expected to increase over thenext years, only the last two options seem to be the most feasible solutions to alleviatethe problem. Accordingly, the general aim of this research work is to develop amethodology to evaluate and quantify aircraft/engines design trade-offs originated as aconsequence of addressing conflicting objectives such as low environmental impact andlow operating costs. More specifically, it is an objective of this work to evaluate andoptimise both aircraft flight trajectories and aircraft engine cycles taking into accountmultidisciplinary aspects such as performance, gaseous emissions, and economics.In order to accomplish the objectives proposed in this project, a methodology foroptimising aircraft trajectories has been initially devised. A suitable optimiser with alibrary of optimisation algorithms, Polyphemus, has been then developed and/oradapted. Computational models simulating different disciplines such as aircraftperformance, engine performance, and pollutants formation, have been selected ordeveloped as necessary. Finally, several evaluation and optimisation processes aimingto determine optimum and ‘greener’ aircraft trajectories and engine cycles have beencarried out and their main results summarised. In particular, an advanced, innovativegaseous emissions prediction model that allows the reliable calculation of emissions trends from current and potential future aircraft gas turbine combustors has beendeveloped. When applied to a conventional combustor, the results showed that ingeneral the emission trends observed in practice were sufficiently well reproduced, andin a computationally efficient manner for its subsequent incorporation in optimisationprocesses. For performing the processes of optimisation of aircraft trajectories andengine cycles, an optimiser (Polyphemus) has also been developed and/or adapted inthis work. Generally the results obtained using Polyphemus and other commerciallyavailable optimisation algorithms presented a satisfactory level of agreement (averagediscrepancies of about 2%). It is then concluded that the development of Polyphemus isproceeding in the correct direction and should continue in order to improve itscapabilities for identifying and efficiently computing optimum and ‘greener’ aircrafttrajectories and engine cycles, which help to minimise the environmental impact ofcommercial aircraft operations.The main contributions of this work to knowledge broadly comprise thefollowing: (i) development of an environmental-based methodology for carrying outboth aircraft trajectory optimisation processes, and engine cycle optimisation-type ones;(ii) development of both an advanced, innovative gas turbine emissions predictionmodel, and an optimiser (Polyphemus) suitable to be integrated into multi-disciplinaryoptimisation frameworks; and (iii) determination and assessment of optimum and‘greener’ aircraft trajectories and aircraft engine cycles using a multi-disciplinaryoptimisation tool, which included the computational tools developed in this work. Basedon the results obtained from the different evaluation and optimisation processes carriedout in this research project, it is concluded that there is indeed a feasible route to reducethe environmental impact of commercial aviation through the introduction of changes inthe aircraft operational rules and procedures and/or in the aircraft/engine configurations.The magnitude of these reductions needs to be determined yet through carefulconsideration of more realistic aircraft trajectories and the use of higher fidelitycomputational models. For this purpose, the computations will eventually need to beextended to the entire fleet of aircraft, and they will also need to include differentoperational scenarios involving partial replacements of old aircraft with newenvironmentally friendly ones.
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