FE - DCA | Dissertações de Mestrado e Teses de Doutoramento
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Browsing FE - DCA | Dissertações de Mestrado e Teses de Doutoramento by Field of Science and Technology (FOS) "Engenharia e Tecnologia::Engenharia Aeronáutica"
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- 3D CFD Combustion Simulation of a Four-Stroke SI Opposed Piston IC EnginePublication . Martins, Maria da Conceição Rodrigues; Brojo, Francisco Miguel Ribeiro ProençaThe reciprocating IC engine plays an important role in the world transport, with very few alternative configurations having commercial success. In light aircraft applications where low vibrations are crucial, boxer engines have predominated. The rising cost of fuel and the growth of public concern over pollutant emissions has led to an increased interest in alternative designs. In recent years, with the uprising of new technologies, research techniques and materials, the OP engine has emerged as a viable alternative to the conventional IC engine in some applications including in the aeronautical field. This study presents a numerical analysis of the combustion process of octane-air mixture in a four-stroke SI opposed piston engine. The model used in the simulations represents the internal volume of the cylinder of UBI/UDI-OPE-BGX286 engine. The simulation was run in Fluent 16.0 software, the species transport model was chosen to model combustion from the available in Fluent, and three different engines speeds were simulated: 2000RPM, 3200RPM and 4000RPM. Regarding the results obtained from the three CFD simulations, the overall behavior and properties of the in-cylinder flow and the obtained graphics were considered acceptable.
- 3D Printed PETG S-Shaped Auxetic Structure: An Experimental and Numerical StudyPublication . Fernandes, Beatriz Teixeira; Dutra, Thiago Assis; Silva, Abílio Manuel Pereira da; Aguiar, Martim Lima deThis dissertation’s main interest is to investigate auxetic structures and their potential applications, especially in the aeronautical sector. Due to the unique properties of these structures, they are increasingly gaining importance in the aeronautical industry for addressing many problems and challenges. Auxetic structures have potential applications in lightweight structures with high mechanical properties and a significant energy absorption capacity. During this study, it is understood that additive manufacturing (AM) plays a crucial role in auxetic structures as it allows the construction of complex structures, such as auxetic structures. After a review of various types of auxetic structures, one structure stood out, not only for its unusual shape but also for its properties. This S-shaped structure stands out for reduced stress concentration, high energy absorption capacity, and high elastic recovery. Due to this distinction, it was decided to study this structure in detail. In this work, several samples of S-shaped structures were manufactured using AM as the manufacturing method and polyethylene terephthalate glycol (PETG) as the material. The samples underwent two types of experimental tests, compression tests, and creep-recovery tests. This allowed obtaining valuable information about the behavior of these structures under load and their recovery after the application of loads. A numerical model was also developed to better understand the S-shaped structure. The numerical model was based on data obtained from the characterization of the PETG material. The simulation results are meticulously compared to experimental data, highlighting the effectiveness of the numerical models despite inherent complexities. Finally, the findings of this work project a promising future for PETG and auxetic structures in various engineering domains, including composites, automotive safety, aeronautics, and aerospace. The foundation established in this work paves the way for future research, enabling a deeper exploration of the possibilities and implications of these innovative materials and structures.
- 3D Simulation of a Detonation Wave in a Rotating Detonation EnginePublication . Serras, Francisca Antunes; Brojo, Francisco Miguel Ribeiro ProençaThe development of efficient propulsion systems is a critical focus in aerospace engineering, and rotating detonation engines (RDEs) present a promising advancement over conventional propulsion technologies because of their compact configurations and high thermal cycle efficiency. In this dissertation, the results of a three-dimensional simulation of a rotation detonation engine using a mixture of hydrogen and air as fuel are presented and discussed. Results from a simulation using a mixture of hydrogen and oxygen are also presented. The simulations were carried out using ANSYS Fluent and all other details of the methodology used are explained in this work. Key aspects of the simulation include the formulation of turbulence and detonation, the engine operating conditions, and the subsequent impact of these operating conditions on the engine performance itself, namely, the initiation and stabilization of the detonation wave. The computational analysis reveals critical insights into the pressure and temperature fields, flame speed, thrust and specific impulse. Stable engine operation was achieved and the detonation wave made four revolutions around the combustion chamber. It was found that when using a mixture of hydrogen and oxygen, detonation did not prevail and deflagration occurred inside the annular combustion chamber. When using a mixture of hydrogen and air, detonation occurred and the engine went into stable operation. The simulation ran for 10220 time steps giving a fluid simulation time of 1022 microseconds. This research contributes to optimizing engine designs with enhanced performance and future research on this matter. The findings have potential implications for the future development of high-efficiency, low-emission propulsion systems, paving the way for advancements, mostly, in the aerospace sector.
- 4D commercial trajectory optimization for fuel saving and environmemtal impact reductionPublication . Ahmed, Kawser; Bousson, KouamanaThe main purpose of the thesis is to optimize commercial aircraft 4D trajectories to improve flight efficiency and reduce fuel consumption and environmental impact caused by airliners. The Trajectory Optimization Problem (TOP) technique can be used to accomplish this goal. The formulation of the aircraft TOP involves the mathematical model of the system (i.e., dynamics model, performance model, and emissions model of the aircraft), Performance Index (PI), and boundary and path constraints of the system. Typically, the TOP is solved by a wide range of numerical approaches. They can be classified into three basic classes of numerical methods: indirect methods, direct methods, and dynamic programming. In this thesis, several instances of problems were considered to optimize commercial aircraft trajectories. Firstly, the problem of optimal trajectory generation from predefined 4D waypoint networks was considered. A single source shortest path algorithm (Dijkstra’s algorithm) was applied to generate the optimal aircraft trajectories that minimize aircraft fuel burn and total trip time between the initial and final waypoint in the networks. Dijkstra’s Algorithm (DA) successfully found the path (trajectory) with the lowest cost (i.e., fuel consumption, and total trip time) from the predefined 4D waypoint networks. Next, the problem of generating minimum length optimal trajectory along a set of predefined 4D waypoints was considered. A cubic spline parameterization was used to solve the TOP. The state vector, its time derivative, and control vector are parameterized using Cubic Spline Interpolation (CSI). Consequently, the objective function and constraints are expressed as functions of the value of state and control at the temporal nodes, this representation transforms the TOP into a Nonlinear Programming (NLP) problem, which is then solved numerically using a well-established NLP solver. The proposed method generated a smooth 4D optimal trajectory with very accurate results. Following, the problem considers generating optimal trajectories between two 4D waypoints. Dynamic Programming (DP) a well-established numerical method was considered to solve this problem. The traditional DP bears some shortcomings that prevent its use in many practical real-time implementations. This thesis proposes a Modified Dynamic Programming (MDP) approach which reduces the computational effort and overcomes the drawbacks of the traditional DP. The proposed MDP approach was successfully implemented to generate optimal trajectories that minimize aircraft fuel consumption and emissions in several case studies, the obtained optimal trajectories are then compared with the corresponding reference commercial flight trajectory for the same route in order to quantify the potential benefit of reduction of aircraft fuel consumption and emissions. The numerical examples demonstrate that the MDP can successfully generate fuel and emissions optimal trajectory with little computational effort, which implies it can also be applied to online trajectory generation. Finally, the problem of predicting the fuel flow rate from actual flight data or manual data was considered. The Radial Basis Function (RBF) neural network was applied to predict the fuel flow rate in the climb, cruise, and descent phases of flight. In the RBF neural network, the true airspeed and flight altitude were taken as the input parameters and the fuel flow rate as the output parameter. The RBF neural network produced a highly accurate fuel flow rate model with a high value of coefficients of determination, together with the low relative approximation errors. Later on, the resulted fuel flow rate model was used to solve a 4D TOP by optimizing aircraft green cost between two 4D waypoints.
- O aeródromo municipal de Castelo Branco como polo gerador de desenvolvimento regionalPublication . Sousa, Miguel Esteves de; Silva, Jorge Miguel dos ReisEste estudo faz uma análise padronizada da importância de um aeródromo na Região Centro (NUT II) de Portugal, centrando-se nos potenciais impactos económicos e sociais decorrentes do desenvolvimento de um dos setores que atualmente mais cresce em termos mundiais. Em termos metodológicos, a dissertação irá recorrer principalmente a motores de pesquisa digitais através da consulta de livros, repositórios, bases de dados, artigos de comunicação social e documentos técnicos das entidades do setor da aviação. Parte o estudo da hipótese de que um aeródromo, articulado com a rede aeroportuária portuguesa, é capaz de transformar a região do país onde se insere, através da captação de população e mão-de-obra qualificada, investimentos e de atividades turísticas, com impacto direto crucial noutros setores, contribuindo, por isso, para a coesão com outras regiões do país. A análise inclui um estudo de caso, na região de Castelo Branco, área marcada pelos problemas que mais afetam a Região Centro, designadamente o afastamento em relação aos centros de decisão, a população envelhecida e em perda, em números absolutos, de ano para ano. No sentido de analisar o potencial de desenvolvimento regional do aeródromo de Castelo Branco, este estudo parte da caracterização da região em termos económicos, geográficos e demográficos, além de caracterizar o aeródromo e de avaliar a sua viabilidade. Para tal, é estabelecida uma comparação com o impacto do Aeródromo de Ponte de Sor, localizado na Região do Alentejo, com uma realidade próxima da de Castelo Branco. Os resultados revelam que o desenvolvimento regional a partir do aeródromo de Castelo Branco é uma realidade, onde ficaram descritas quais as condições que mais favorecem este desenvolvimento, bem como os desafios que existem e que poderão condicionar o desenvolvimento do seu aeródromo.
- Aerodynamic Analysis of a Forward–Backward Facing Step Pair on the Upper Surface of a Low-Speed AirfoilPublication . Freitas, Luís Gonçalo Azevedo; Gamboa, Pedro VieiraThe Long Endurance Electric Unmanned Air Vehicle (LEEUAV) is a project of a green, low-cost, small footprint electric solar UAV which was designed for civilian surveillance applications, such as coast, forest, or border patrol. Therefore, long endurance is desired, which is accomplished by a lightweight airframe design and an electric propulsion system assisted with solar cell arrays. The LEEUAV has an approximated mass of 5 kg, 4.5 m of wingspan and an 8-hour flight endurance. To ease the construction, its wing, in addition to its aerodynamic function, must accommodate the solar cells on its upper surface. Since the solar cells have a finite thickness, they create an offset, with a forward facing step at the beginning of the solar cell array and a backward facing step at its end. These two steps affect the aerodynamic performance of the wing mainly because the forward facing step forces the transition of the flow from laminar to turbulent. The aim of this thesis is to study the influence of these steps in the aerodynamic coefficients of the LEEUAV’s airfoil, having as variables the offset’s position, length, and thickness. To do this, a numerical analysis was performed initially using XFOIL, an interactive program for the analysis of subsonic airfoils, and then ANSYS Fluent, a commercial computational fluid dynamics (CFD) software. First, in XFOIL, a total of 444 combinations of offsets were tested, in order to understand the range of positions that could be more appropriate for placing the solar cells. After this initial study, another analysis was performed to better understand their most appropriate positions, considering their precise thickness and length. Afterwards, a small amount of combinations was chosen to perform a CFD analysis that served to validate and refine the results obtained from XFOIL. Since there was no experimental data regarding the LEEUAV’s airfoil, several turbulence models were initially tested to see which best resembled the XFOIL’s solution. Subsequently, an analysis of the selected combinations was performed and the best position for placing the solar cells, based on the performed analysis, is between 21% and 23% of the airfoil’s chord.
- Aerodynamic Analysis of a Two-Man BobsleighPublication . Ribeiro, Simão Rafael Silvério; Gamboa, Pedro VieiraBobsleigh is a highly competitive winter sport in which technological advancements play a crucial role in optimising performance, with aerodynamics being a key factor in race outcomes. This study presents a comprehensive aerodynamic analysis of a two-man bobsleigh using Computational Fluid Dynamics (CFD) simulations to investigate flow structures and drag sources, with the objective of improving aerodynamic efficiency through geometric modifications. A baseline bobsleigh geometry was developed using photographic references of high-performance designs from recent competitions. CFD analyses were conducted in ANSYS Fluent, employing the Realizable ?? - ?? turbulence model with Non-Equilibrium Wall Functions for near-wall modelling. Key aerodynamic characteristics, such as flow separation regions and pressure distributions were identified and studied. Simulations were performed at two distinct free-stream velocities: 15 ??/??, representative of the late push start phase, and 35 ??/??, corresponding to race-speed conditions. Additional analyses were conducted to evaluate the influence of confining walls in straight track sections on bobsleigh aerodynamic performance. Based on these findings and existing research, an iterative design process was conducted to develop an improved geometry aimed at reducing aerodynamic drag. The enhanced design incorporates modifications to the front bumper, ground clearance, and diffuser geometry, resulting in a 6.37% reduction in aerodynamic drag and a 3.14% increase in maximum speed.
- Aerodynamic Breakup of a Single Droplet due to a CrossflowPublication . Carrolo, Gabriel Alexandre da Costa; Silva, André Resende Rodrigues daThe present experimental work focuses on the aerodynamic breakup study of unconventional fuels. This process refers to the secondary atomization of a drop due to a cross-flow, where different velocities cause several regimes and structures appear amidst drop deformation of Jet Fuel mixtures with HVO (hydroprocessed vegetable oil) and water. The excessive use of fossil fuels has led humans to find viable and environmentally beneficial alternatives for use in various types of engines and combustion processes. With this, the use of biofuels has been one of the most sought after alternatives, and its employment in the aeronautical and aerospace sector is an example of the beneficial use of these fuels. This dissertation’s objective is to visualize and study the dynamic behaviour of a drop at the transition points between regimes, for different crossflow velocities. The drops are composed of: Jet Fuel 100%, Jet Fuel 75% - 25% HVO, Jet Fuel 50% - 50% HVO, and H2O (used as reference fluid). Considering that present legislation in the aeronautical sector allows a minimum concentration of 50% Jet Fuel in volume makes the choice of mixtures used in this study have a more restricted criterion, and therefore other mixtures are not considered. For this, an experimental facility is designed and built. Consisting of a high-speed camera, allowing the ability to visualize all the mechanisms inherent to the secondary atomization of a drop, with a specific trigger activation and desired frame rate; an infusion pump, which allows control of the insertion rate of drops into the working section. Through flat-head needles with two different internal diameters, drops of the same size are produced for all fluids; backlighting through led strips behind a diffuser glass help standardize the light captured by the camera; a properly calibrated wind-tunnel to is necessary to reach the desired speeds for regime transitions. Using the existing literature, a comparison of the phenomena and secondary atomization regimes for this new group of mixtures is made. After the dynamic study of these mechanisms, the conclusions are drawn regarding the maximum deformation rate of a drop, taking into account the dimensionless characterization of time and the dimensionless groups of relevance for this study. Drop trajectory is also presented for each regime and fluid, and a new correlation is proposed for maximum cross stream diameter evolution due to time.
- Aerothermodynamic analysis of an experimental rocket aimed to test micro-launcher technologiesPublication . Vale, João Pedro Simões; Brojo, Francisco Miguel Ribeiro Proença; Coelho, Tiago Marchão Moreira; João Alexandre AbreuThe current decrease in satellite size, associated with the rise in their launch rates, has created a market demand for a new class of launchers. This new class, known as micro launchers, can only put a fraction of the current launcher’s payload into orbit but can deliver micro and small satellites to their desired orbit for a fraction of the price. Due to this new demand, the European Space Agency has supported this market trend with programs that enable the development of the necessary technologies for these future micro-launchers. In this context, Omnidea leads a project to develop an experimental vehicle that aims at developing and testing these technologies in a relevant flight environment. The development of this dissertation is in the framework of this project and focus on performing an aerothermodynamic analysis of the experimental rocket through numerical simulations in subsonic, transonic and supersonic flight. These numerical simulations are performed for two different geometries, and one additional study case is dedicated to the engine on condition. The results are then used for an aerodynamic and thermodynamic study of the vehicle and, when possible, are compared to similar studies with a satisfactory agreement. Furthermore, is discussed the impact that the alterations between the rocket geometry have on the flow around the vehicle, and their cause, as well as their consequences, are pointed out. Regarding the engine on condition, it is possible to see the creation of several new flow disturbances and their impact on the thermodynamic and aerodynamic models. Additionally, some concerns about these new flow disturbances are raised, and suggestions are made for their correction. At last, this study also shows the CFD’s key role in providing data for the construction of aerothermodynamic databases of spacecraft.
- Air budJets: A VTOL virtual operator company in PortugalPublication . Duarte, Manuel Mendes; Silva, Jorge Miguel dos ReisThe aeronautical industry is evolving very rapidly mainly due to the development of technology. These technological advances have allowed the Man to develop projects that are very ambitious as is the case of "flying cars". This concept has been developed since the '80s, but only now have arisen prototypes capable of satisfying this dream. With this, the appearance of VTOL aircraft, aircraft capable of taking off and landing vertically, without needing any runways to do so. For this project, helicopters are not considered as VTOL aircraft because they are not very energy efficient. Many companies have developed VTOL aircraft, with design and consequently characteristics very different from each other, but having in common being hybrid or fully electric aircraft. For this study, a "fictitious" airline company was created using VTOL aircraft. The service characterization was then carried out, where using localization algorithms and trajectory optimization, we were able to elaborate an application (software) that treats the data of the flights to the marked ones by clients to optimize the routes/trajectories of the flights. Then the elaboration of a model and a business plan was made, and it is possible to observe the viability of the economic-financial results of the new (fictitious) company.