Departamento de Ciências Aeroespaciais
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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 CFD Simulation of a Cold Flow Four-Stroke Opposed Piston EnginePublication . Gonçalves, Robert Silva; Brojo, Francisco Miguel Ribeiro ProençaA CFD simulation of a four-stroke opposed piston engine has been performed. It is intended to evaluate the overall behavior and properties of in-cylinder flow, in a way that its use comercialy can be achieved. Due to the inherent characteristics of an opposed piston engine, it is necessary to dimension the model, using as reference the Jumo 205E engine: both valves, as well as the combustion chamber and both exhaust and admission ports. A combustion chamber adjacent to the cylinder zone is placed in order to fit both valves. The commercial software Fluent 14.0 is used to perform the numerical calculations. Due to the complexity of this study, mostly because of the existence of moving parts, the use o dynamic meshing is necessary. The viscous model is Standard K-E; the port entry and exit are defined as pressure-inlet and pressureoutlet, respectively. PISO and PRESTO! are the chosen methods for pressure-velocity coupling and pressure space discretization, respectively. The final results obtained were far from the expected, mainly due to the inadequate behavior and properties of the fluid within the cylinder and ports.
- 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 Simulations of Droplets Impacting Liquid Films: Crown Parameters MeasurementsPublication . Vasconcelos, Daniel; Ribeiro, Daniela; Silva, R. D.; Barata, Jorge M MThe 3D incompressible Navier-Stokes equations are coupled with the CLSVOF method and employed to numerically simulate the phenomena of single droplet impact onto liquid films. A solution-adaptive mesh refinement tool, based on the gradient of the volume fraction scalar, is adopted in order to reduce computational cost. Three different fluids are taken into account: 100% jet fuel and 75%/25% and 50%/50% of jet fuel and biofuel, respectively. Quantitative analysis of the crown height and outer diameter is performed for different impact conditions, such as the influence of the impact velocity and dimensionless thickness, between experimental and numerical results, and the qualitative analysis includes the occurrence of splashing and overall crown evolution. Numerical results show that the crown outer diameter measurements are in good agreement with the experimental cases, presenting a slight discrepancy for the lower liquid film thickness of h*= 0.2. The crown height measurements are under-predicted for the current model, maintaining a similar trend for dimensionless thicknesses of h*= 0.5 and h*= 1 while, for the lower thickness, the crown disintegrates at earlier stages. The crown curvature and rim instabilities exhibit significant differences, and the splashing phenomenon occurs for both the experimental and numerical outcomes.
- 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.
- 4D Fuel Optimal Trajectory Generation from Waypoint NetworksPublication . Ahmed, Kawser; Bousson, KouamanaThe purpose of this thesis is to develop a trajectory optimization algorithm that finds a fuel optimal trajectory from 4D waypoint networks, where the arrival time is specified for each waypoint in the network. Generating optimal aircraft trajectory that minimizes fuel burn and associated environmental emissions helps the aviation industry cope with increasing fuel costs and reduce aviation induced climate change, as CO2 is directly related to the amount of fuel burned, therefore reduction in fuel burn implies a reduction in CO2 emissions as well. A single source shortest path algorithm is presented to generate the optimal aircraft trajectory that minimizes the total fuel burn between the initial and final waypoint in pre-defined 4D waypoint networks. In this work the 4D waypoint networks only consist of waypoints for climb, cruise and descent phases of the flight without the takeoff and landing approach. The fuel optimal trajectory is generated for three different lengths of flights (short, medium and long haul flight) for two different commercial aircraft considering no wind. The Results about the presented applications show that by flying a fuel optimal trajectory, which was found by implying a single source shortest path algorithm (Dijkstra’s algorithm) can lead to reduction of average fuel burn of international flights by 2.8% of the total trip fuel. By using the same algorithm in 4D waypoints networks it is also possible to generate an optimal trajectory that minimizes the flight time. By flying this trajectory average of 2.6% of total travel time can be saved, depends on the trip length and aircraft types.
- 4D waypoints based optimal trajectory generation for unmanned aerial vehiclesPublication . Gameiro, Tiago Alexandre; Bousson, KouamanaThe constant technological developments recently observed on unmanned aerial vehicles allow its use on diverse activities. With the arrival of new opportunities new challenges arrive as well. Nowadays the navigation methods used is limited to following pre-defined points in space, waypoints, by using the flight parameters values in its control. This work proposes an alternative method, consisting in creating trajectories from 4D waypoints, i.e. three spatial coordinates plus a temporal one. So, it is possible to foresee the path e guarantee that it will be on the desired place at the right time. Because passing through the exact position of a waypoint is rather difficult and not always required, a tolerance is used around it, allowing the passage on the vicinity defined by a sphere whose radius is equal to that tolerance. In this work an algorithm is proposed to find the tridimensional point in the interior of that said sphere which minimizes the path length between the previous and next waypoint. The trajectory is defined interpolating the waypoint coordinates, using a fifth order polynomial function. This way, it is possible to constrain said function in order to create a trajectory whose flight parameters comply with navigation limits associated with the vehicle. By using the limits associated with a small unmanned aerial vehicle, it was possible to create a trajectory defined by 4D waypoints with a consistent behavior and quite smooth. The path chosen is a Racetrack Pattern loiter defined by six waypoints whose time was defined in order to attempt to maintain a constant velocity through the path. The simulation was a successfully performed, being the limits imposed respected through the entire domain of time. Therefore, the possibility of creating 4D waypoint based trajectories is proven, generating a new area of opportunities for time based missions where time plays a critical role, or the shape of the path is crucial.
- Adaptação de injeção eletrónica em motor alternativo de carburadorPublication . Teixeira, Fabio Paulo Fernandes; Brojo, Francisco Miguel Ribeiro ProençaO presente trabalho teve como objetivo principal a substituição do carburador por injeção eletrónica num motor Honda Gx120, com a finalidade de diminuir o consumo específico do mesmo. Este motor equipou o veículo de baixo consumo da equipa responsável pelo projeto UBICAR, do Departamento de Engenharia Eletromecânica da Universidade da Beira Interior, que participou na prova Shell Eco Marathon. Para a realização deste projeto foi necessário realizar alguns estudos a fim de perceber qual as melhores adaptações e componentes a utilizar no motor, obtendo o máximo rendimento possível. Posto isto, procedeu-se as alterações necessárias no motor para aplicação dos componentes essenciais ao funcionamento do mesmo. Foi ainda elaborado um banco de ensaios mecânico a fim de testar o desempenho do motor já alterado, servindo este também para testar motores até 500cc. Por fim realizaram-se testes na prova Shell Eco Marathon e no banco de ensaios onde se retiraram valores de potência, binário e consumo específico.
- Adaptive gurney flap for rotor bladesPublication . Dias, Bruno Ricardo Barros; Gamboa, Pedro Vieira; Silva, José Miguel Almeida daDesde muito tempo vários esforços tem sido feitos de maneira a optimizar o rotor dos helicópteros com o objectivo de reduzir a emissão de poluentes. Durante vários anos foram feitas várias optimizações estrutrais na pá do rotor. Estudos recentes numéricos e experimentais mostram que para melhor a performance do rotor várias considerações aerodinâmicas têm que ser levadas em conta. O principal objectivo deste trabalho é estudar e optimizar um mecanismo preliminar constituído por um flap dinâmico que consiga controlar a camada limite na pá. O flap escolhido foi o Gurney Flap, desenvolvido nos anos 70 por um piloto de automóveis com o intuito de provocar uma downforce de maneira a melhorar o desempenho do automovél. A razão desta escolha deve-se por o flap ter uma superfície relativamente pequena com baixas forças de inércia permitindo baixos consumos de energia e sem adicionar extra carga para na pá. A utilização deste flap demonstrou o aumento as propriedades aerodinâmicas de pá, portanto, reduzindo o consumo de combustÃvel. Para este estudos várias análises estruturais foram realizadas usando softwares comerciais entre eles; análises cináticas, de maneira a estudar o deslocamento, velocidade e aceleraçao do mecanismo e também do sistema de actuação; análises dinâmica, possibilitando o calculo de tensões e deformações do sistema sujeito a várias cargas de inécia e por fim uma análise modal, bastante importante devido ao mecanismo estar sujeito a uma frequência de actuação. Depois de conduzidas estas análises foi possivél optimizar o peso da desenho inicial em cerca de 50% respeitando todos os requerimentos impostos e as características do material. Foram estudados dois tipos de sistema de de actuação deixando em aberto a escolha do actuador.
- ADS-B- automatic dependent surveillance broadcast: estudo do impacto em PortugalPublication . Rodrigues, Cláudia Vanessa Coutinho; Silva, Jorge Miguel dos ReisNo paradigma actual de CNS/ATM, (Communication, Navigation, Surveillance/Air Traffic Management), o sistema ADS-B representa uma importante ferramenta para melhoria da vigilância, aumentando a eficiência da gestão de tráfego aéreo, o que se traduz em maiores parâmetros de segurança e menores atrasos. Em todo o mundo desenvolvem-se projectos e programas para implementação da tecnologia do sistema ADS-B, com testes envolvendo ANSPs (Air Navigation Services Providers), avaliando as funções dos controladores de tráfego aéreo, operadores avaliando as tarefas dos pilotos, além de fabricantes de aviónicos e aeronaves, com objectivo de aquilatar a eficiência, segurança e custo deste novo sistema. O objectivo deste trabalho consiste em avaliar as ineficiências que se verificam actualmente no Grupo Central dos Açores, estudar o impacto da implementação de um sistema ADS-B nessa zona, tendo em conta as tecnologias actualmente utilizadas para posterior integração. Adicionalmente, efectuou-se uma abordagem à problemática custo-benefício, bem como uma avaliação de carácter operacional sobre a utilização mais racional do espaço aéreo.