São José dos Campos, Brazil
São José dos Campos, Brazil

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Rego I.S.,Federal University of ABC | Toro P.G.P.,Institute Estudos Avancados | Minucci M.A.S.,Vale Solucoes em Energia | Chanes Jr. J.B.,Institute Estudos Avancados | And 2 more authors.
Journal of Aerospace Technology and Management | Year: 2013

Scientists at the laboratory of Força Aérea Brasileira (FAB) have demonstrated experimentally that laser-induced "air spikes" (DEAS) may reduce effectively both total vehicle drag and heating at hypervelocities. Now, we apply the Rayleigh flow to directly determine the degree of reduction in vehicle drag and convective heat flux into the airframe of a hypersonic blunt-body when laser energy is added upstream of the flight path. Our numerical findings are in accordance with the physical trends observed in our previous hypersonic laser-induced DEAS experiments.

Fernandes L.M.,Brazilian Technological Institute of Aeronautics | Freitas R.B.,Brazilian Technological Institute of Aeronautics | Mendonca M.T.,Brazilian Technological Institute of Aeronautics | Flatschart R.B.,Vale Solucoes em Energia | Pantaleao A.V.,Vale Solucoes em Energia
50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition | Year: 2012

The present study investigates the performance of film cooling in gas turbine applications when two cooling jets are used. The cooling air issuing from one hole interferes with the jet from a second hole and the resulting flow field at first may either degrade cooling performance or improve it. Care must be taken to ensure that the typical counter rotating vortices associated with jets into a main stream do not interact to uplift the cooling film. Preliminary results published else where for normal jets into a cross stream are presented here in order to illustrate the main results of jet interaction. The present investigation extends those preliminary results for jets injected at an angle of 30 degree, typical of gas turbine cooling applications. Copyright © 2012 American Institute of Aeronautics and Astronautics, Inc.

Freitas R.B.,Brazilian Technological Institute of Aeronautics | Fernandes L.M.,Brazilian Technological Institute of Aeronautics | Mendonca M.T.,Brazilian Technological Institute of Aeronautics | Pantaleao A.V.,Vale Solucoes em Energia | Flatschart R.B.,Vale Solucoes em Energia
50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition | Year: 2012

The secondary air system in gas turbines is responsible for distribution of cooling air to hot sections and sealing in roller bearings and gaps between rotating and stationary components. They usually contain labyrinth seals to provide controlled pressured drop along a series of cavities separated by sharp fins. The secondary air system for cooling and sealing can account for more than 20% of the mass flow in the engine, having a significant impact on the thermodynamic efficiency. The precise control of cooling mass flow is mandatory in order to avoid overheating or excessive cooling mass flow. There are a number of empirical correlations relating mass flow to pressure drop as a function of labyrinth seal geometry. Manufacturing cost, maintenance and reliability are other relevant parameters to be considered in seal design. The present analysis aims at the evaluation of a proposed labyrinth seal configuration in terms of fin width to pitch length ratio and cavity geometry. The investigated labyrinth seal is used on the last stage of a five stage axial compressor. A less demanding configuration in terms of manufacturing cost is compared to a more usual configuration to access the sealing quality of the proposed labyrinth. Mass flow versus pressure drop are investigated and correlations for discharge coefficient are compared based on numerical simulations. The flow streamlines in both configurations are compared for the actual topology consisting of a radial inlet followed by a 90 degree bend just before the first fin. Numerical simulations are performed using an open source control volume based CFD code (OpenFoam) to solve the two-dimensional compressible Reynolds averaged Navier-Stokes equations. The results show that the least expensive manufacturing configuration results in flow parameters that are different from the standard configuration by no more than about 5%. Adding grooves to the stationary wall change flow parameters by another 3%. Comparisons between the original design and the modified design reveals that the same discharge coefficient as the original design may be obtained with only three fins after the modifications. Copyright © 2012 by the American Institute of Aeronautics and Astronautics, Inc.

Da Silva E.B.,Brazilian Technological Institute of Aeronautics | Assato M.,Vale Solucoes em Energia | De Lima R.C.,Vale Solucoes em Energia
Proceedings of the ASME Turbo Expo | Year: 2013

Usually, the turbogenerators are designed to fire a specific fuel, depending on the project of these engines may be allowed the operation with other kinds of fuel compositions. However, it is necessary a careful evaluation of the operational behavior and performance of them due to conversion, for example, from natural gas to different low heating value fuels. Thus, this work describes strategies used to simulate the performance of a single shaft industrial gas turbine designed to operate with natural gas when firing low heating value fuel, such as biomass fuel from gasification process or blast furnace gas (BFG). Air bled from the compressor and variable compressor geometry have been used as key strategies by this paper. Off-design performance simulations at a variety of ambient temperature conditions are described. It was observed the necessity for recovering the surge margin; both techniques showed good solutions to achieve the same level of safe operation in relation to the original engine. Finally, a flammability limit analysis in terms of the equivalence ratio was done. This analysis has the objective of verifying if the combustor will operate using the low heating value fuel. For the most engine operation cases investigated, the values were inside from minimum and maximum equivalence ratio range. Copyright © 2013 by ASME.

Santos A.P.,Vale Solucoes em Energia | Andrade C.R.,Brazilian Technological Institute of Aeronautics
Journal of Aerospace Technology and Management | Year: 2012

For geographic regions where significant power demand and highest electricity prices occur during the warm months, a gas turbine inlet air cooling technique is a useful option for increasing output. Inlet air cooling increases the power output by taking advantage of the gas turbine's feature of higher mass flow rate, due the compressor inlet temperature decays. Industrial gas turbines that operate at constant speed are constant-volume-flow combustion machines. As the specific volume of air is directly proportional to the temperature, the increases of the air density results in a higher air mass flow rate, once the volumetric rate is constant. Consequently, the gas turbine power output enhances. Different methods are available for reducing compressor intake air temperature. There are two basic systems currently available for inlet cooling. The first and most cost-effective system is the evaporative cooling. Evaporative coolers make use of the evaporation of water to reduce the gas turbine inlet air temperature. The second system employs two ways to cool the inlet air: mechanical compression and absorption. In this method, the cooling medium flows through a heat exchanger located in the inlet duct to remove heat from the inlet air. In the present study, a thermodynamic analysis of gas turbine performance is carried out to calculate heat rate, power output and thermal efficiency at different inlet air temperature and relative humidity conditions. The results obtained with this model are compared with the values of the condition without cooling herein named of Base-Case. Then, the three cooling techniques are computationally implemented and solved for different inlet conditions (inlet temperature and relative humidity). In addition, the gas turbine was tested under different cooling methods for two Brazilian sites, and comparison between chiller systems (mechanical and absorption) showed that the absorption chiller provides the highest increment in annual energy generation with lower unit energy costs. On the other hand, evaporative cooler offered the lowest unit energy cost but associated with a limited cooling potential.

Monteiro V.G.,Brazilian Technological Institute of Aeronautics | Zaparoli E.L.,Brazilian Technological Institute of Aeronautics | de Andrade C.R.,Brazilian Technological Institute of Aeronautics | de Lima R.C.,Vale Solucoes em Energia
Journal of Aerospace Technology and Management | Year: 2012

This work has presented the first stage performance at design and off-design operating points of an axial turbine, with two stages using a numerical simulation. Experimental methods of predicting the performance of axial turbine is costly and time consuming compared to the computational fluid dynamics approach. Therefore, computational techniques were adopted to determine the stage performance. This study analyzed the first stage performance of an axial flow turbine, using a computational tool for simulating the steady state two/three-dimensional viscous flow. A computational fluid dynamics software was used to solve the rans equations with the spalart-allmaras turbulence model. The computational fluid dynamics results were compared with those obtained from the mean line loss model code. The comparisons have been conducted to provide a pretest performance for the turbine first stage.

Paulino I.,National Institute for Space Research | Takahashi H.,National Institute for Space Research | Vadas S.L.,Colorado Research Associates | Wrasse C.M.,Vale Solucoes em Energia | And 4 more authors.
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2012

Medium-scale gravity waves (MSGWs) observed during the Conjugate Point Experiment (COPEX) at Boa Vista (2.8°N; 60.7°S, dip angle 21.7°) have been ray-traced and studied based on zero wind and model wind conditions. Wind profiles have been used from the TIE-GCM and HWM-07 models. Temperature profiles were used from the NRLMSISE-00 and TIE-GCM models, and TIMED/SABER satellite data. Doppler up-shifted MSGWs, at ~ 87 km of altitude, propagated to higher altitudes into the thermo-sphere-ionosphere domain than waves that were un-shifted. Most MSGWs propagated upwards up to ~ 140 km of altitude and were seen to be unlikely candidates to trigger equatorial plasma bubbles (EPBs) at the F layer bottom side. However, three of them propagated up to heights close to the F layer bottom side, where it could act in the EPB seeding directly. Moreover, three MSGWs, which propagated equatorward, could act on EPB seeding by field-line-integrated effects. © 2012 Elsevier Ltd.

Lopez R.H.,INSA Rouen | Lemosse D.,INSA Rouen | De Cursi J.E.S.,INSA Rouen | Rojas J.,Vale Solucoes em Energia | El-Hami A.,INSA Rouen
Engineering Optimization | Year: 2011

This article aims at optimizing laminated composite plates taking into account uncertainties in the structural dimensions. As laminated composites require a global optimization tool, the Particle Swarm Optimization (PSO) method is employed. A new Reliability Based Design Optimization (RBDO) methodology based on safety factors is presented and coupled with PSO. Such safety factors are derived from the Karush-Kuhn-Tucker optimality conditions of the reliability index approach and eliminate the need for reliability analysis in RBDO. The plate weight minimization is the objective function of the optimization process. The results show that the coupling of the evolutionary algorithm with the safety-factor method proposed in this article successfully performs the RBDO of laminated composite structures. © 2011 Taylor & Francis.

Takahashi H.,National Institute for Space Research | Shiokawa K.,Nagoya University | Egito F.,National Institute for Space Research | Murayama Y.,Japan National Institute of Information and Communications Technology | And 2 more authors.
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2013

Upper mesosphere airglow emissions and temperature observed at Rikubetsu (43.5°N,143.8°E) and mesospheric winds observed at Wakkanai (45.4°N,141.8°E), Japan, from January to December 2005 were used to analyze periodic oscillations of 2-16 days. During the January to March period and after September, both winds and airglow demonstrated clear 8-, 10- and 16-day oscillations. Downward phase progressions observed in the oscillations indicate that these are a signature of Rossby mode planetary waves. The 16-day wave was more evident in the zonal wind than the meridional. The 10-day wave was observed in January and March, on the basis of only a few cycles superposed on the 16-day wave. Airglow OI 557.7nm, O2 and OH(6,2) band emissions and O2 rotational temperature also showed significant amplitude of oscillation induced by the wave passages. For the 10-day wave, OI557.7nm showed an amplitude of oscillation equals to or more than 50% of the mean intensity level, O2 ~45% and OH ~25%. Large amplitudes of oscillation of the airglow during the passage of planetary waves suggest the possible vertical transport of atomic oxygen in addition to the density and temperature variations intrinsic to the wave events. © 2013 Elsevier Ltd.

Prestes A.,University of Paraíba Valley | Rigozo N.R.,National Institute for Space Research | Nordemann D.J.R.,National Institute for Space Research | Echer E.,National Institute for Space Research | And 4 more authors.
Pure and Applied Geophysics | Year: 2014

Evidence of the solar activity modulation of the Earth’s climate has been observed on several parameters, from decadal to millennial time scales. Several proxies have been used to reconstruct the paleoclimate as well as the solar activity. The paleoclimate reconstructions are based on direct and/or indirect effects of global and regional climate conditions. The solar activity reconstructions are based on the production of the 14C isotope due to the interaction of cosmic ray flux and the Earth’s atmosphere. Because trees respond to climate conditions and store 14C, they have been used as proxies for both for climate and solar activity reconstructions. The imprints of solar activity cycles dating back to 10,000 years ago have been observed on tree-ring samples using 14C data, and those dating back to 20 million years ago have been analyzed using fossil tree-growth rings. All this corresponds to the Cenozoic era. However, solar activity imprints on tree rings from earlier than that era have not been investigated yet. In this work, we showed that tree rings from the Mesozoic Era (of ~200 million years ago) recorded 11- and 22-year cycles, which may be related to solar activity cycles, and that were statistically significant at the 95 % confidence level. The fossil wood was collected in the southern region of Brazil. Our analysis of the fossils' tree-ring width series power spectra showed characteristics similar to the modern araucaria tree, with a noticeable decadal periodicity. Assuming that the Earth’s climate responds to solar variability and that responses did not vary significantly over the last ~200 million years, we conclude that the solar–climate connection was likely present during the Mesozoic era. © 2013, Springer Basel.

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