Numerical study of spray dispersion in a premixing chamber for Low-NOx engines

The present work describes a numerical study of a confined two-phase flow under high-pressure conditions, typical of gas turbine combustors. An Eulerian frame was used for the gas phase together with a Lagrangian approach to describe the dispersed phase. The computational method was extended to high-pressure environments, which are more representative of the practical gas turbine operating conditions. The results are compared with experimental data, and revealed the ability of the model to increase the knowledge of the turbulent dispersion phenomena for this type of practical conditions (high pressure and confined flow).Fundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio

Comparison of Commercial and Open-Source CFD Solvers on Surface Tension Dominated Flows

Problems involving multiphase flows require a physical understanding of how the phenomenadevelop and the specific interactions they manifest. For surface tension relevant flows, suchas bubbles and droplets, the importance of modelling and predicting small-scale behaviouris crucial in accurately defining the liquid-gas interface and complex interactions that may takeplace. Axisymmetric numerical simulations of single droplets impacting onto thin liquid films areperformed using commercial and open-source CFD codes. ANSYS Fluent®is the commercialsoftware employed, whereas Basilisk is the open-source CFD solver adopted. The incompress-ible Navier-Stokes equations are coupled and handled differently throughout each software.A solution-adaptive mesh refinement tool is adopted to reduce computational cost. Softwarecomparison is based on quantitative and qualitative analysis, namely crown height and outerdiameter measurements, and the crown curvature and occurrence of splashing, respectively.Results show that Basilisk simulations are in good agreement with the experimental data. Fluent follows the tendency for the crown outer diameter however, in terms of height, the modelunder-predicts its growth and collapses at later stages of the impact for lower thicknessesFundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio

Liquid film dynamic on the spray impingement modelling

The present paper addresses a liquid film sub-model included into a computational model that aims at reproducing the spray impingement phenomena. This numerical extension incorporates the spread of the liquid film over the neighbouring nodes due to the dynamic motion induced by the film inertia but also the exchange of mass between the liquid layer and the incident and splashing particles. Moreover, the dimensionless film thickness parameter is introduced into the sub-model by mean of an experimentally-deduced correlation that can be fitted and updated to specified conditions. In order to realize how the model behaves with different influencing parameters, a thorough investigation is performed: the results that are obtained with and without the liquid film sub-model are compared against the experimental data for two crossflow rates. The integration of the computational extension with the spread/splash transition criterion is also evaluated by considering two types of transition criteria: one that takes into account the effect of the film thickness and one that does not. The results show that the latter option in combination with the sub-model do not distinctly enhance the simulation results, contrary to what happens using the transition criterion that considers the film thickness as an influencing parameter. In this case, the model with the computational extension reveals better prediction results than the one without it, which indicates the necessity of considering the liquid film formation for spray impingement simulations but also a splash threshold that takes into account the influence of the film thickness.Fundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio

Spray impingement modelling: Evaluation of the dissipative energy loss and influence of an enhanced near-wall treatment

The goal of the present research is to contribute to improve the knowledge about the spray impingement topic through a numerical study that is aimed at investigating the impact of using the dissipative energy terms that are available in the literature when they are embedded into a specific dispersion model. Comparing all the numerical approaches, a non-negligible disagreement is observed between the relationship proposed in the original model and the other ones drawn from the literature. This fact evidences the influence of the energy dissipated term on the secondary atomization outcome. The present work also provides a comprehensive study on the estimation of the energy dissipated during the splash event. This is a major contribution to the permanent literature since the few works found only addressed the spread regime. In addition, this paper gives an in-depth analysis on the influence that an enhanced treatment of the boundary layer in the region close to the wall may have in the simulation of such flows. The work revealed that this near-wall droplets tracking method provides an alternative way to increase the accuracy of the dispersed phase and achieve more consistent results without the necessity of a direct mesh refinement.Fundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio

Influence of the Spread/Splash Transition Criteria in the Spray Impingement Modeling

The present paper reports a numerical study of a spray impinging on a surface through a crossflow. This work is intended to study the influence of the spread/splash transition criteria in the modeling of the spray impingement phenomenon. Several experimental correlations available in the literature are inserted in the same base model and the results are tested against experimental data. It can be concluded that the employment of an accurate transition criteria can improve the quality of the results.Fundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio

The History of the Portuguese Aviation - A Summary

This article is intended as a summary of a new area of study on the History of the Portuguese Aeronautics and Aerospace and addresses issues such as: the forthcoming of the aircraft at Portugal, its military and civilian use; the scope of early days concerning Portuguese intercontinental flights and their authors; the development of air navigation devices by Portuguese inventors in the 1920s and 30s; the Aeronautics industry and the need to develop expertise in Aeronautical/Aerospace Engineering in Portugal during the centuries XX and XXI.Fundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio

First Aerial South Atlantic Night Crossing

The history of the transatlantic flights began in 1919 when Albert C. Read’s team flew between Newfoundland and Lisbon, with a stopover at Azores, for fuel and repairs. The flight was made following a chain of 60 U.S. warships in order to guide it along its route and to provide assistance if needed. Two weeks later, John Alcock and Sir Arthur Whitten Brown made the first nonstop transatlantic flight from Newfoundland to County Galway, Ireland, covering more than 3000 km in just 16 hours of flight. In 1922, Gago Coutinho and Sacadura Cabral crossed the South Atlantic Ocean by air, for the first time using only internal means of navigation: a modified sextant and a course corrector; both devices proved its effectiveness. The Portuguese Aeronautics rejoiced auspicious days that time, with its aviation pioneers trying consecutively to reach more distant places along intercontinental flights. Several Around-the-World Flight Attempts were made in 1924: United States, England, France, Portugal, Argentina and Italy. However the circumnavigation purpose was only officially confirmed before the general public, when a considerable flying progress was achieved. In 1923, Gago Coutinho and Sacadura Cabral were contemplating to perform an Around the World Flight, a dream pursued also by Sarmento de Beires in 1924 and 1927. In 1927 and by following the knowledge obtained by Coutinho and Cabral, four Portuguese Airmen started an Around the World Flight Attempt in a mission that ended with seaplane sunk at the Ocean; however this mission was renamed after the seaplane loss and became known in the World as the First Aerial South Atlantic Night Crossing. For the first time in history, during the night of 16 to 17 March 1927, a Portuguese crew flew 2595 km over the Atlantic Ocean from Guinea, Africa to Fernando de Noronha Island, Brazil. The flight was made only by astronomical processes navigation resources that proved again to be absolutely feasible and trustworthy, regardless day or night lighting conditions.Fundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio

The First Aerial Journey from Portugal to Macau

On 1920, Brito Pais and Sarmento Beires tried an unsuccessful flight attempt from Amadora, Lisbon to Madeira Island onboard an airplane Breguet XIV A2, named “Cavaleiro Negro”. Despite the scarce means of navigation both navigators managed to reach Madeira, which failed to land due to dense fog. On their way back after 8 hours of flight time, they alight at the Atlantic Ocean for lack of fuel and were rescued at about 500 km from Lisbon. On 1922, Gago Coutinho and Sacadura Cabral conducted the First Aerial Cross of the South Atlantic, flying from Lisbon to Rio de Janeiro. The Portuguese Aeronautics rejoiced auspicious days that time, with its aviation pioneers trying consecutively to reach more distant places along intercontinental flights. On 1923, Gago Coutinho and Sacadura Cabral were contemplating to perform an Around the World Flight. However, Sacadura died in 1924, while piloting an airplane acquired for the circumnavigation voyage. Later on 1924 the pilots Brito Pais and Sarmento Beires idealized the conducting of an aerial flight from Lisbon to Macau as an aspiration for a future Portuguese Around the World Flight attempt: on 7 April 1924, those pilots departed from Vila Nova de Milfontes in a Breguet XIV Bn2 airplane, starting their Journey to Macau. During a flight stage on 7 May an engine failure forced them to crash the airplane at India; on 30 May, both pilots managed to continue the Voyage in a De Havilland DH9 aircraft before being forced to end their attempt in 20 June in flying over Macau. A typhoon hindered their efforts to land and the airplane was crash landed in Chinese Territory about 800 meters from the Hong Kong Border. On 25 June 1924, they were shuttled back to Macau by boat. Brito Pais, Sarmento Beires and Manuel Gouveia returned to Portugal, via North America, visiting several Portugueses nuclei at China, Japan, United States and England. They went to Portugal on 9 September, after having flown a total of 16,760 km in 117:41 h facing often extremely adverse atmospheric conditions, sandstorms and inaccurate navigation maps.Fundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio

Gago Coutinho and the Scientific Navigation

Gago Coutinho, jointly with another Portuguese aerial navigator, managed to perform the First Flight from Europe to the South Atlantic in 1922, a Journey exclusively guided by internal means of navigation. Despite Coutinho being a person with multi-purpose activity on several areas of knowledge, he became known and glorified in the World in 1922, as an air navigator, a position that he achieved due to an aerial navigation device that he also had invented. Coutinho developed a new sextant model that could be used to measure the altitude of a star (when flying overseas) without the need of the sea horizon. This new device was called precision sextant and was provided with an artificial horizon line defined with the help of a water bubble. Due to his knowledge of Navigation, Astronomy, Geography and Mathematics, Coutinho received from the Portuguese King D. Carlos I, several assignments at Africa and Asia. Gago Coutinho received several important official medals and prizes, including the Ph.D. Honoris Causa from the Universities of Lisbon and Oporto and authored several scientific publications. Coutinho 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

The splash deposition transition limits of a biofuel droplet wall impact with a and without crossflow

Over the last years, there have been many investigations into new ways to obtain clean and efficient energy production. In this spirit, this study aims to successfully adapt low emission aero-engines combustors to burn biofuels. Biofuels are the immediate alternative to fossil-fuel powered aero-engines, given that by regulation is possible to apply today, a biofuel into the aeronautical industry. There are some regulations to have into account, being the biggest one the fact that the new blend must be constituted of at least 50% of conventional jet fuel (JF). In this work were selected four blends to study: 100% JF; 75% JF and 25% NEXBTL (biofuel); 50% JF and 50% NEXBTL and H2O. A smooth, dry aluminium plate was used as the impact surface and the objective was to observe the splash-deposition limits and characterize the dynamic behaviour of the droplets with and without crossflow. Different velocities of the crossflow were chosen and the impact angle of the droplet was also analysed. The splash-deposition threshold was also compared with those proposed by other authors.Fundação para a Ciência e a Tecnologia (FCT)info:eu-repo/semantics/publishedVersio