Departamento de Ciências Aeroespaciais
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Browsing Departamento de Ciências Aeroespaciais 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.
- 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.
- 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 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.
- Air Transport Performance and Global Decision AnalysisPublication . Baltazar, Maria Emília da Silva; Silva, Jorge Miguel dos ReisSince the beginning of aviation, airports have played a pivotal role in Aeronautical Engineering. The airport concept has changed a lot over the past century from small airfields to international hubs. These airport infrastructures have played a significant role in the economic development of the regions they operate. The emergence of the airport city concept as a new successful organisational model suggests that any infrastructure of this kind to be competitive should adopt it. With all its inputs and outputs, the airport industry significantly influences the global economy. The balance between the public interest in general, shareholders, and airport operators must seek to be reconciled. I was investigated how it would be possible to determine whether an airport would have the expected impact on the economy at different scales. Those scales could be that of a continent, a country, a region, or even a city and establish the decision criteria for building (or not) new airport infrastructures and making improvements (or not) in them. Searching for tools that would allow an appropriate evaluation of the management processes of an airport, the measurement of the position of the airport compared to its counterparts (benchmarking) is essential. However, the complexity of the models used makes this tool unfriendly for airport administration. Apart from that, the essential focus of this type of study is the land side of the airport. Nevertheless, there are other types of studies for evaluating the performance of airport processes. Still, these are also complex and do not involve all operational, financial and agent components near the airport. The studies review reinforces the idea that a global analytical tool is essential to find the global perspective (airside, landside, and agents) of any airport's performance beyond the challenges that will be put to them soon and a complete benchmark of direct competitors. The construction of a new methodology requires that airport, land, and airside infrastructures be considered, and agents near the airport, customers, shareholders and airport operators. Thus, a well-founded analysis for a Global Decision Analysis (GDA) incorporates all the infrastructure stakeholders' interconnections in a single tool. GDA is, therefore, friendlier to stakeholders given the management and optimization of decisions based on an analysis system based on the MACBETH multi-criteria methodology, the PESA-AGB. This tool was built and applied to an airport with dimensions identical to Lisbon airport, demonstrating and comparing the evolution of performance and efficiency over 11 years from 2003 to 2013 by six key performance areas of the airport and the respective key performance indicators. The development of an airport efficiency tag for each year of assessment was implemented. An APE-Label implementation, applied to any airport, is presented, and discussed in this study regardless of its size and location. The main obstacle to implementing this APE-Label is the heterogeneity of the airport infrastructure since it differs in the number of runways for public, private or even public-private property, among others. However, with the PESA-AGB methodology, it was possible to mitigate this factor. The main proposal is to provide a graphical APE-Label that informs all interested parties which infrastructure assessment is analysed across the six key performance areas each year that will help to maximize performance and efficiency standards. For the airport case study, a self-benchmarking analysis was carried out for the airport's study with distinctive characteristics representing the central Portuguese air infrastructure. The airport in study is considered the largest in terms of passengers, movements and cargo and is associated with Lisbon airport. Finally, the results of PESA-AGB and GDA have been presented in two visual analysis panels. The dashboards and the GDA report and recommendation are prepared.
- Aircraft Attitude Tracking using a Model Reference Adaptive ControlPublication . Castanho, Emanuel da Costa; Bousson, KouamanaA discrete-time explicit Model Reference Adaptive Control (MRAC) with constant trace algorithm is applied to a linearized aircraft model during longitudinal and lateral-directional motions in order to test the performance of this type of control during specific flight conditions. The model was obtained through system identification with data generated from the linearized state equations of the F-4C. In the longitudinal case the aircraft behaves like a Single-Input-Single-Output (SISO) system and simulations are performed for two examples of pitch angle data, in which two expressions for the control (classic and penalized) are applied in each example to compare their performance. In the lateral-directional case the airplane behaves like a Multi-Input-Multi-Output (MIMO) system with equal number of inputs and outputs and the MRAC control law must be modified to describe a decoupling process. Simulations are performed in order to verify if the controller is able to handle the coupling relation between some variables, such as lateral velocity, roll angle, aileron angle and rudder angle. The adaptive control in both study cases and for the chosen initial conditions showed good tracking when following the reference output, presenting no drift problems. The choice of the initial simulation conditions is also analyzed, in order to prevent actuator saturation.
- Airfoil Improvement on Horizontal Axis Wind Turbine Suitable for Local Construction in Underdeveloped CountriesPublication . Miguel, João Carlos Tavares; Silvestre, Miguel Ângelo Rodrigues; Monteiro, João Manuel Milheiro Caldas PaivaThis dissertation purpose is to study the impact that a geometry modification of a wind turbine rotor imposes on its performance. The studied wooden rotor, with a diameter of 1.2 m, belongs to a family of small wind turbines that are built by unskilled persons using hand tools with the guidelines of Hugh Piggott. Due to its inaccuracy, the production process delivers a geometry with sharp leading edges. For the performance of an airfoil, the leading edge is one of the most important characteristics to take in mind, and so, the goal of this dissertation was to smooth the airfoils leading edge towards the lower surface in order to widen the ????- ?? curve of the rotor. To do so, numerical methods were employed to assess such modification on the performance, in a way that the technique could be later applied on the rotor using nothing but hand tools. In a previous investigation, the same rotor here approached in this dissertation, was numerically and experimentally studied for the following windspeeds: 3.0; 3.7; 4.4; 5.5; 7.2 e 7.7 m/s. In the same study, a digital scan was performed on the rotor, one for each blade, resulting in 6 different cross sections each with its chord and incidence angle. The three blades present geometric differences. Having these airfoils characteristics, the QBlade software was used for the design and analysis of the new modified airfoils based on the original Piggott airfoils. The software also allows for rotor design and uses the Blade Element Momentum Theory for the analysis of horizontal axis wind turbines. The performance of both rotors was approximated by averaging the performance of three ideal rotors, each consisting of three identical blades 1,2 and 3. The new airfoils regarding blade 1 and 3, presented better aerodynamic efficiency performance compared to the Piggott airfoils, whereas blade 2 new airfoils did not exhibited any significant improved performance compared to the Piggott airfoils.The dimensionless simulations results from QBlade, portrayed that the averaged rotor with the modified airfoils present better power coefficient (????) for high values of ?? (ratio between the tangential velocity of the blade tip and the free stream windspeed) when compared to the averaged rotor with the Piggott airfoils. For a constant rotational speed of 500 RPM, the new rotor remarkably withdraws more energy from the flow for low windspeeds. In a hypothetical approach of a optimized turbine production made up by the best modified airfoils, the optimized rotor simulations showed a significant better performance for high values of ??,as well as higher maximum ???? than the ones from the averaged rotor with the modified airfoils.