University of Beira Interior
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On the Modeling of a Spray Impinging on a Surface
No full textThe present paper reports a numerical study of a spray impinging on a surface through a crossflow and is aimed at studying the fundamental aspects of the spray impingement phenomena in a three-dimensional configuration, which is relevant to practical engines. Different impinging models were used and the results are compared with measurements and predictions of other authors. The results show a general good agreement with the experiments, and reveal that the splash droplets are very important for the spray development. The performance of droplet impinging models depends strongly on the conditions of pre-impingement.Fundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio
Aircraft Emissions in Airports - The LPPT Case
No full textA 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.Fundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio
On the modelling of spray/wall impingement under crossflow conditions
No full textSpray impingement is an important phenomenon affecting a wide variety of applications. In the present study, numerical simulations are carried out for predicting the outcome of such flows. An empirical procedure is used to define the initial spray characteristics, which relies on a comprehensive set of free spray measurements. The computer model is evaluated by comparing the numerical simulations against experiments on spray impacting on a solid surface with the presence of a crossflow. The predicted results show a reasonable agreement with the measurements. Moreover, further results are presented on the formation and evolution of the liquid flim distribution over time.Fundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio
Gago Coutinho and the Aircraft Navigation
No full textGago Coutinho was one of the two Portuguese navigators that crossed by air the South Atlantic in the beginning of the 20th century. He developed a new model of sextant that could be used to measure the altitude of a star when flying without the need of the sea horizon. This new instrument was called "precision sextant" and used an artificial horizon line which was defined with the help of a water bubble. Due to his knowledge of Navigation, Astronomy, Geography and Mathematics he received from the Portuguese King D. Carlos I several assignments in Africa and Asia. Gago Coutinho received several important official medals and prizes, including the PhD Honoris Causa from the Universities of Lisbon and Oporto, and authored several scientific publications. He received the distinct position of Admiral of the Portuguese Navy in 1958, and died in the following year.Fundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio
Influence of the Energy Dissipation in the Spray Impingement Modeling
No full textSimulating the complex dynamic phenomena that occur during the spray droplets impact is of great interest in numerous applications. In this sense, refine flexible dispersion models that can be adjusted through the use of adapted and more suitable empirical correlations in order to fit specific configurations with minimum time constraints would be a great asset both for industry and researchers. In this work, it is intended to study the dissipative energy term in the splash event. Besides the original relationship proposed in the dispersion model used, other equations of energy dissipation based on investigations devoted to the study of this parameter are introduced in the simulation and the results are tested against experimental data. Comparing all the relationships evaluated, the ones drawn from the literature deviates from what was expected. Therefore, it is evident that further research are essential in this field in order to propose a sub-model that could accurately define the energy dissipation term during the splash regime, whereas the investigations carried out so far only considered the energy loss through viscous dissipation during the spread regime.Fundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio
Numerical Study of an Array of Evaporating Droplets Through a Crossflow
No full textThe present paper presents a numerical study on evaporating droplets through a turbulent crossflow. The aim of this study is to evaluate and improve an Eulerian/Lagragian approach to account for turbulent dispersion, evaporation and coupling between both processes in spray systems. A method developed to study isothermal turbulent dispersion is extended to the case of an array of evaporating droplets, using two different evaporation models. Droplet diameter, temperature and mass fraction distributions were found to be strongly dependent on the evaporation models used.Fundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio
Sacadura Cabral and the Dawn of Portuguese Aviation
No full textSacadura Cabral was one of the two Portuguese navigators that crossed by air the South Atlantic in the beginning of the 20th century. From 1901 to 1915 Sacadura was at Mozambique and Angola where he developed geodetic and geographical missions of the greatest importance for Portuguese interest at Africa. With the Great World War requirements as a Navy Officer with 34 years old he decided to serve Portugal at the Aviation. In 1915 he went to France and obtained its pilot license. In 1916 Sacadura returned to Portugal and begun its instructor pilot career. He developed the “path corrector” which he created to compensate the drift caused by wind. In 1922 Sacadura made the First Air cross from Europe to South Atlantic. In 1923 he proposes himself to make an attempt to the First Air Circumnavigation Journey. He developed all its possible efforts to initiate this journey in March of 1924; however some delays had forced him to postpone the journey. Sacadura received important official medals and prizes, including the PhD Honoris Causa from the Universities of Lisbon and Oporto. In 1924 he died before he could carry out its Circumnavigation Air Journey.Fundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio
Unsteady Computations of a Ground Vortex
No full textA computational study of the impact zone of a wall jet with a boundary layer was performed for a wide range of velocity ratios, VR, from 0.065 to 0.2. A ground vortex is formed and for intermediate velocity ratios the flowfield exhibits an oscillating behavior. The location and size of the ground vortex is almost constant during the complete sequence of oscillation, but secondary vortexes may also appear. For the case of very low velocity crossflow (small VR) the computations exhibit a stationary solution, which is in agreement with previous numerical and experimental results. For strong crossflows (large VR) the flow is also stationary, although there is a transition regime of some unsteadiness without any secondary vortex present.Fundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio
The Influence Of Liquid Film Thickness On Crown Development: Crown Sheet Angle
No full textDroplet impact upon a liquid film is a phenomenon widely observed in nature but also extensively reported in the literature for a variety of different applications [5]. Fuel injection in internal combustion engines is one of the many applications of studying this type of impact. Among all possible outcomes of a single droplet impinging on a liquid wall, crown splash is one of the most studied phenomena. Yet, it is not completely understood and several researchers seek to understand all physical mechanisms involved and their features. In previous works, [6] focused their work on a specific phenomenon that follows crown splash. Bubble encapsulation happens when the crown liquid sheet bends inwards and eventually the jets on top of the crown merge creating an empty bubble above the horizontal liquid film as shown in Fig. 1. The formation mechanism of this phenomenon is not completely understood, but the crown sheet angle α certainly plays a significant role in its formation. In this way, crown development was investigated for a range of different impact parameters to understand how the crown sheet angle evolves after impact and until the crown collapse.Fundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio
Computational study on coaxial nitrogen-hydrogen injection at supercritical conditions
No full textIn the present work, we perform a computational study on the mixing of nitrogen and hydrogen at supercritical conditions. A coaxial injection configuration is considered where nitrogen is injected through the central post with a hydrogen co-flow. The flow in both injectors as well as in the combustion chamber is considered in the computations. This preliminary version presents the radial density profiles maximum of both species and radial density profiles at selected locations.Fundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio