Browsing by Issue Date, starting with "2012-11-06"
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- Twin Impinging Jets Through a CrossflowPublication . Barata, Jorge M M; Neves, Fernando M. S. P.; Vieira, Diana; Silva, AndréLaser Doppler measurements provide information on the flowfield created by twin impinging jets aligned with a low velocity crossflow. The experiments were carried out for a Reynolds number based on the jet exit conditions of Re j=4.3×104, an impingement height of 20.1 jet diameters and for a velocity ratio between the jet exit and the crossflow V R=Vj/Uo of 22.5, and an interjet spacing of S=6D. The results show a large penetration of the first (upstream) jet that is deflected by the crossflow and impinges on the ground, giving rise to a ground vortex due to the collision of the radial wall and the crossflow that wraps around the impinging point like a scarf. The second jet (located downstream) it is not so affected by the crossflow in terms of deflection, but due to the downstream wall jet that flows radially from the impinging point of the first jet it does not reach the ground. The results indicate a new flow pattern not yet reported so far, that for a VSTOL aircraft operating in ground vicinity with front wind or small forward movement may result in enhanced under pressures in the aft part of the aircraft causing a suction down force and a change of the pitching moment towards the ground.
- The History of Aerospace/Aerospace/Aeronautics Engineering in PortugalPublication . Barata, Jorge M. M.; Neves, Fernando M. S. P.; Silva, AndréIn the present study the origins of the aeronautics engineering education in Portugal are investigated, as well as the relations between the different initiatives that occurred in the beginning of the twentieth century. This paper aims at reporting the most relevant initiatives in Portugal and the actors involved. From 1963 to 1974 the Portuguese Air Force in together with a Portuguese University taught the first Aeronautics Engineering Military Degree at Portugal. In early 1990s two Portuguese Universities and the Portuguese Air Force started their Aerospace/Aeronautics Engineering Degrees teaching. In the 21st Century the Aerospace/Aeronautics Engineering courses at Portugal are connected with the most advanced Engineering Schools in Europe providing skills and competences integrating several disciplines.
- Identification of Gas Turbine Ground Vortex Formation RegimesPublication . Barata, Jorge M M; Manquinho, Pedro; Silva, AndréIn the present paper the preliminary work of Barata et al.11 on gas turbine ground vortex formation is extended to include eighteen different engines that are presently in service. The ground vortex flows produced by each engine are compared and discussed for the corresponding operational condition. The results have shown that more than one mode can occur for a particular engine-velocity ratio-clearance distance combination with 1, 2 or 3 vortexes that may merge before entering the inlet engine. Further improvement of gas turbine design is then required to prevent hazardous operation of aircrafts in the airports.
- Evaluation of Numerical Variable Density Approach to Cryogenic JetsPublication . Antunes, Eduardo Luís Santos Farias; Silva, André; Barata, Jorge M MThe present work is devoted to study cryogenic nitrogen jets in high subcritical conditions. Fuel injection is one of the great challenges in engineering of diesel engines, gas turbines and rocket engines, combining in the last one also the injection of oxidizer. It is widely known that the increase of operation pressures and temperatures increases engine efficiency and reduces fuel specific consumption. Thus, it is a general trend in modern engines the operation in increasingly higher pressures. However at higher chamber pressures the injected fluids may experience ambient conditions exceeding the critical values. Several authors stated that at these conditions the injected fluids suffers a change of its properties, and the traditional two-phase flow models cannot correctly predict the jet behavior at these conditions, thus new computational models are needed for these specific conditions. Barata et al. [18] performed a numerical investigation aimed to evaluate the applicability of an incompressible but variable density model in liquid jets under sub-to-supercritical conditions. The results achieved agree well with the experimental data but they only considered intermediate density ratios from 0.05 to 0.14. The objective of the present work was to extend the investigation of Ref. 18 to lower density ratios from 0.025 to 0.045 which correspond to cases with subcritical chamber pressures. The obtained results agree well with the experimental and numerical data of Chehroudi et al. presented in Ref. 18. It was also found in this work that the computational model does not offers valid results for density ratios lower than 0.025.
- Influence of the Energy Dissipation in the Spray Impingement ModelingPublication . Rodrigues, Christian; Barata, Jorge M M; Silva, AndréSimulating 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.