ICI - AeroG-LAETA | Documentos por Auto-Depósito
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- 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.
- Advanced statistical analysis of the collision of wall jet with a boundary layerPublication . Silva, André; Panão, Miguel; Barata, Jorge M MLaser-Doppler measurements of the velocity characteristics of a ground vortex flow resulting from the collision of a wall jet with a boundary layer are analyzed using advanced statistical tools. Namely, finite mixtures of probability density functions, which determine the best fitting using a Bayesian approach based on a Markov Chain Monte Carlo (MCMC) algorithm. This approach takes into account eventual multimodality and heterogeneities in velocity field distributions. Therefore, it provides more complete information about the probability density function of multimodal velocity distributions and allows the identification of characteristic velocities in the heterogeneous data. The experiments are performed for a wall jet-to-boundary layer velocity ratio of 2, and include mean and turbulent velocity characteristics along the two normal directions contained in planes parallel to the nozzle axis. The results, which have relevance to flows encountered by VSTOL aircraft, quantify the structure of the complex ground vortex flow. The results revealed that in the collision zone the rms velocity fluctuation appears to be overestimated for the horizontal component, probably due to the measured velocity range, oscillating between positive and negative values. The results revealed that finite mixture was able to accurately reconstruct a mathematical function describing the probability distribution obtained experimentally. The results shows that U and u'rms rms provide an idea of the flow dynamics, their use is limited and an important amount of information associated with the highly curved flow complexity is lost, preventing a more accurate description of turbulent structures emerging from the collision of wall jet with a boundary layer.
- Aerial Journey from Portugal to Timor, Macau, India, and Return (1934)Publication . Neves, Fernando M. S. P.; Barata, Jorge M M; Silva, AndréIn the 1920s and 1930s, a group of Portuguese Aviation Pioneers added the name of Portugal to the History of Aviation, essentially by performing Aerial Journeys to Portuguese Colonies. East Timor was an outlier until 1934. Thus, Humberto Amaral da Cruz conceived and designed an Aerial Journey from Portugal to East Timor, Macau, India, and return, with the primary purpose to highlight the country's relevance and consolidation as a colonial power as a demonstration of sovereignty over its most distant domains. With the help of a national public subscription, a government subsidy, and the support of some private entities, he purchases a De Havilland DH. 85 aircraft. Between October 25 and December 21, the pilot, and his mechanic, António Lobato, accomplish their Journey of 42,670 km in 268 hours and 25 minutes. The pilots' reception was apotheotic, with enormous national pride, followed by the feeling of dignity and expansion of the Portuguese Nation. The Journey had a global impact through the massive propaganda effort from distant countries in the Far East and a vast national influence through the rapprochement and consolidation of the Portuguese colonial empire in the most remote places in the World. Humberto da Cruz demonstrated his skills as a pilot, his skill as an officer, and the strength of his upstanding character. In particular, he praised aviation for developing a new era on earth, arguing that Portugal would have to adopt this form of communication between its overseas territories, Brazil, and the rest of the World.
- Aerodynamic Breakup of a Single Droplet due to a Crossflowed AirstreamPublication . Carrolo, Gabriel Alexandre da Costa; Ribeiro, Daniela; Barata, Jorge M M; Silva, A. R. R.The main breakup regimes are visualized and studied with the help of a high-speed camera and a continuous jet of air, provided by a wind tunnel, is used to transition the droplet into the various stages of secondary atomization. The use of Jet Fuel and Biofuel mixtures is the focal point of this study. All the known regimes are encountered and each transitional We is calculated. The variation of We due to Oh is described, in addition to the comparison between We number thresholds and correlations existent in the literature for each regime transition. The influence of these numbers on the dimensionless characterization of time and later the maximum cross stream diameter is shown. Finally, a correlation for the temporal evolution of the drops’ cross stream diameter for all regimes, assuming its deformation is not a linear function of time, is proposed.
- Aircraft Emissions in Airports - The LPPT CasePublication . Barata, Jorge M M; Correia, Paulo Jorge Lopes; Silva, AndréA new methodology to predict the aircraft emissions in airport vicinity is presented. The application to the LPPT airport is discussed, and the results revealed that the emissions are dependent on the flight schedules and strongly affected by the aircraft/engine combinations.
- An Experimental Study of Terrain-Induced Airflow at the LPPI AirportPublication . Barata, Jorge M M; Medeiros, Rui Fernando da Costa; Silva, AndréThe present paper reports a study of the airflow around Pico Island in the Azores and the problems it represents to the operation of aircraft at the island airport. A statistical study of the wind data collected at Pico and Faial Island was carried out to find discrepancies that can be attributed to the flow around Pico Mountain. A wind tunnel visualization of the flow around the Island was conducted, in order to identify some of the characteristics of the flow under different wind directions at the airport site. With this data, some assumptions of the best runway to use and where the most problematic phenomena should be encountered in the approach areas were made.
- Analysis And Visualization Of The Perturbations Imposed On The Liquid Film By Crown Sheet Collapse Or ClosurePublication . Ribeiro, Daniela; Panão, Miguel; Barata, Jorge M M; Silva, A. R. R.Bubble encapsulation is a phenomenon that results from droplet impact on a liquid film for very specific impact conditions. After splashing, the crown liquid sheet starts to bend inwards, and eventually, the jets at the top of the crown merge and form a perfect empty bubble. This bubble bursts due to the impingement of a secondary droplet that falls in the spherical dome or by reaching its critical thickness. However, bubble encapsulation is seldom reported in the literature. Due to that, this work focuses on understanding better its dynamics and formation mechanisms. By using a bottom perspective of the phenomenon, important information about its dynamics is disclosed. From the bottom shadowgraphs, the capillary waves and the perturbations imposed on the steady liquid film are clearly observed. From previous works, it was confirmed that its occurrence is systematic, so, one of the goals of this study is to realize how the impact conditions influence the phenomenon and if we can establish a criterion for its occurrence. Despite the scarce information about the phenomenon, there are some works about it that are focused on the cavity underneath the bubble. In this study, we observed the cavity and conclude that the cavity shape does not influence the bubble encapsulation phenomenon. Finally, the crown closure time was measured for a specific set of impact conditions and it was analyzed depending on the dimensionless thickness of the liquid film.
- Asteroid Impacts on the Ocean and Its Short-term Consequences: a Portuguese Case StudyPublication . Morais, Renato; Santos, Luís; Silva, A. R. R.; Melício, RuiAny location on Earth might be considered a subject to an asteroid impact because, as previous studies show, they are a proven global threat. the consequences of a collision could be catastrophic, even though such events are rare to occur in a person’s lifetime. Tsunami waves can constitute the greatest threat as the Earth’s surface is mostly water, making the probability of a water impact greater than a ground impact. This work expands the knowledge about asteroid impacts on the ocean and their short-term regional consequences. Three asteroids were assumed to impact the Earth: (1) the 2015 JJ asteroid with a 130 m diameter, (2) the 2020 FA5 asteroid with a 210 m diameter, and (3) the Apophis asteroid, a 370 m wide asteroid. We evaluated the consequences of all impacts, at a 45 degree angle, for a specific case study, where the chosen impact location was the midpoint between Portugal’s mainland, Azores, and Madeira Islands. The cratering process, overpressure, induced thermal radiation, and tsunami waves were assessed, along with the global effects. The overpressure mainly causes structural damage. The thermal radiation has too short a range to reach the studied localities. The tsunami is undoubtedly the most far-reaching and threatening effect of an asteroid impact in the ocean.
- Book of abstracts: 4th EJIL LAETA Young Researchers MeetingPublication . Silva, André; Neves, Fernando M. S. P.; Moleira, Filipa; Quental, Carlos; Belinha, Jorge; Arteiro, Albertinho; Almeida, MiguelThe 4th LAETA Young Researchers Meeting (4EJIL 4º Encontro de Jovens Investigadores do LAETA) is held from November, 9th to 10th of 2017 in Covilhã, Portugal. Since its beginning, the EJIL is a continuous source of sharing state-of-the-art developments in the scientific and technological fields of Energy, Transports and Aeronautics and a large number of applications in the field of Mechanical Engineering. This meeting also offers a unique opportunity for joining young researchers of LAETA (Laboratório Associado de Energia, Transportes e Aeronáutica) units, namely: IDMEC, INEGI, ADAI, and AeroG. One main objective of this meeting is the promotion and encouragement of interdisciplinary discussions among young researchers. This Book of Abstracts contains the synthesis of the papers accepted for oral presentation and is organized by the Thematic Research Lines of LAETA, which cover the research fields of Energy, Aeronautics and Space, Advanced Manufacturing, Advanced Materials, Biomechanics, Fires, Engineering Design and Engineering Systems. On behalf of the Organizing Committee, I would like to express our gratitude to those who contributed to the success of this meeting. The assistance provided by the Advisory Committee is highly appreciated. A special thanks also goes to the participants and the authors, without whom the 4EJIL, and this book, would not be possible. And last, but not least, I would like to manifest my sincere gratitude to my colleagues of the Organizing Committee not only for the efficient work performed but especially for the friendly and helpfulness environment lived during the time of preparation of the meeting.
- Centennial 1922–2022: First Transoceanic Flight with Autonomous Aerial NavigationPublication . Neves, Fernando M. S. P.; Barata, Jorge M M; Silva, AndréAlthough the Transoceanic Flights had already piqued the state's attention, the airplane's lack of aerial navigation equipment rendered it unsuitable for this new trend in 1919. Three years later, in 1922, Sacadura Cabral and Gago Coutinho conducted a Transoceanic Flight to demonstrate the autonomy and usefulness of the Sextant with an artificial horizon, in combination with novel air navigation instruments, all handled by a simplified short air navigation method. Unfortunately, due to errors induced by the vertical dynamics associated with the aircraft's speed, the sextant was constantly adjusted to the sea horizon rather than the perfect readings of the artificial horizon. This condition required a search for a suitably clear horizon line, forcing the seaplane's altitude to be often lowered. Furthermore, a few supplementary navigation devices risked their initial autonomous air navigation. Nonetheless, by measuring the size of the wingspan shadow reflected on the ocean's surface, the pilots managed to adjust their expertise to maintain the seaplane on the planned trajectory. Furthermore, this novel and reliable steering method allowed them to perform trigonometric calculations to estimate their height, which was critical in calculating the aircraft's positioning. Thus, the Journey was recognized as a significant milestone in aviation history, ushering the use of the sextant as a key means of air navigation and proving the effectiveness of a revolutionary principle of Coutinho's short methods, never before documented on Astronavigation. Along with the First Transoceanic Flight with Autonomous Aerial Navigation, one of the itineraries featured an 11 ½ hour crossing the Atlantic from Cape Verde to St. Peter and St. Paul Rocks. When it is remembered that they managed to reach this remote and a pretty small destination (a few hundred ft long and the highest point 60 ft above the water) after a flight of nearly 900 nautical miles over the Ocean, it exalts the remarkable feat of the airmen.