Browsing by Issue Date, starting with "2015-01-03"
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- Pressure Based Comparison of Different Gas Turbine Ground Vortex FlowsPublication . Barata, Jorge M M; Manquinho, Pedro; Silva, AndréThe present paper has the previous work of Barata et al in mind and has the purpose of analyzing the behavior of ground vortex flows through several values of height of the engine axis above the ground, diameter of engine intake and inlet airflow velocity using pressure on the ground and in a 3D scale for that.
- The First Aerial Raid From Portugal to MacauPublication . Neves, Fernando M. S. P.; Barata, Jorge M M; Silva, AndréIn 1920, Brito Pais and Sarmento de Beires tried an unsuccessful flight attempt from Amadora, Lisbon to Madeira Island aboard the airplane Breguet XIV A2, named "Cavaleiro Negro". Despite the scarce means of navigation they reach Madeira, which failed to land due to dense fog. On the 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. In 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. In 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. Also in 1924 the pilots Brito Pais and Sarmento de Beires idealized the conducting of a trip 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 XVI Bn2 airplane, beginning a trip to Macau. On 7 May an engine failure forced them to crash in India. On 30 May they 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 de 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 16760 kilometers in 117: 41h facing often extremely adverse atmospheric conditions, sandstorms and inaccurate navigation maps.
- Modelling of Drop Deformation and BreakupPublication . Rodrigues, Christian; Barata, Jorge M M; Silva, AndréThe present paper addresses the macroscopic atomization characteristics of liquid-fuel droplets when subjected to the infuence of a high velocity air crossfow. A breakup model is conceived by using a set of correlations available in the literature with the purpose of replicating such phenomena. The computational results are compared against experimental data to validate the model. The results show a reasonable agreement between measurements and predictions in both qualitative and quantitative outcomes evaluated, which sustain the mathematical formulation adopted. However, further improvements may be aspired given the fact that there is a lack of experimental data available when shearing effects come into play in the mechanisms occurring during the atomization process. On the other hand, the use of two fuels (diesel and bio-diesel) allowed to perceive a relevant impact of the liquid properties (particularly surface tension and viscosity) in the characteristics of the fragments resulting from the breakup event.
- First Aerial South Atlantic Night CrossingPublication . Neves, Fernando M. S. P.; Barata, Jorge M M; Silva, AndréThe history of the transatlantic flights began in 1919 when Albert C. Read’s team flew an NC-4 flight between Newfoundland and Lisbon, Portugal with a stopover at Azores Islands, for fuel and repairs. The flight was made following a chain of 70 US warships in order to guide it along its route and 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. Gago Coutinho and Sacadura Cabral crossed the South Atlantic Ocean by air in 1922, using only internal means of navigation: a modified sextant and a course corrector. For the first time in the aviation history a transatlantic flight was accomplished using exclusively astronomical and estimated navigation processes. Both devices proved its effectiveness. In 2 March 1927 and by following all the knowledge obtained by the First Cross of the South Atlantic, Sarmento de Beires, Jorge Castilho, Duvalle Portugal and Manuel Gouveia started a new mission that became known as the First Aerial South Atlantic Night Cross. 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.
- RANS Modeling of Transcritical and Supercritical Nitrogen JetsPublication . Antunes, Eduardo Luís Santos Farias; Silva, André; Barata, Jorge M MThe present work is dedicated to the study of cryogenic nitrogen jets under supercritical chamber conditions with the objective of simulating the process of fuel injection inside a combustion engine. In order to do so, a numerical simulation using a RANS model was performed over two case studies previously analyzed by other authors both in experimental and numerical studies. The result obtained by the present numerical approach were then compared with previous results and this way accessed the capabilities of RANS approach using a k-ε turbulence model in which the density is calculated through the mixture fraction value to correctly model cryogenic jets at supercritical conditions. The results show the ability to achieve good agreement with other studies for the axial density distribution however for other parameters like the jet spreading angle the same agreement was not found.
- Numerical Simulation of Twin Impinging jets in Tandem through a CrossflowPublication . Vieira, Diana; Barata, Jorge M M; Neves, Fernando M. S. P.; Silva, AndréThe flow field of ground vortex generated by twin impinging jets in tandem through a crossflow is numerically studied in detail. Numerical simulation and visualization are presented for two turbulent circular jets emerging into a low velocity cross stream, impinging after on a flat surface perpendicular to the geometrical jet nozzle axis. The numerical study is based in experimental studies done early, so all the features of the experimental flow were maintained when the numerical simulation was performed. The Reynolds number used was based on the jet exit conditions of 43,000 to 105,000, a jet to crossflow velocity ratio of 22.5 to 43.8, an impinging height of 20.1 jet diameters and an interject spacing’s of S=5D and L=6D. The analysis of the flow was extended to regions and flow conditions for which no measurements have been obtained in last experimental studies, i.e., for velocity ratios of 15 to 90. The numerical results show that for the smallest velocity ratios the jets initially do not mix, but remain together in two layers. Three different types of flow regimes were identify, therefore when VSTOL aircrafts operating in ground vicinity, only the regime with strong impingement on ground and with a formation of a ground vortex is relevant. The numerical results allowed to extend the last experimental studies, and prove that the deflection of the rear jet is due to the competing influences the wake, the shear layer, the downstream wall jet of the first jet and the crossflow.
- On the Modelling of Evaporating Sprays Impinging onto Solid SurfacesPublication . Rodrigues, Christian; Barata, Jorge M M; Silva, AndréThe present paper presents a numerical study on evaporating droplets impinging onto a solid surface through a crossflow. The characteristics of the initial spray are established by employing an empirical procedure, which relies on a comprehensive set of free spray measurements. Distinct wall and crossflow temperatures are analysed systematically to evaluate the in fluence of droplets evaporation on the nal outcome of spray impingement, and, particularly, on the distribution of the thin liquid lm over the surface. The present computational model already proved to deliver accurate predictions of the spray/wall interactions under different conditions. In this work, the conditions are extrapolated to a heated environment, which reproduce more adequately what is found in in-cylinder situations. The computational model is adapted to meet the new requirements and perform within the range of conditions for which it is now formulated. The analysis shows that higher temperatures lead to smaller impinging droplets, an increase in the number of depositing droplets but a decrease in the fraction of mass of particles contributing to the liquid film; and a more uniform distribution of the liquid layer over the surface.