983 resultados para Rocket engines


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"September 1991."

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Converging swirling liquid jets from pressure swirl atomizers injected into atmospheric air are studied experimentally using still and cine photographic techniques in the context of liquid-liquid coaxial swirl atomizers used in liquid rocket engines. The jet exhibits several interesting flow features in contrast to the nonswirling liquid jets (annular liquid jets) studied in the literature. The swirl motion creates multiple converging sections in the jet, which gradually collapse one after the other due to the liquid sheet breakup with increasing Weber number (We). This is clearly related to the air inside the converging jet which exhibits a peculiar variation of the pressure difference across the liquid sheet, DeltaP, with We. The variation shows a decreasing trend of DeltaP with We in an overall sense, but exhibits local maxima and minima at specific flow conditions. The number of maxima or minima observed in the curve depends on the number of converging sections seen in the jet at the lowest We. An interesting feature of this variation is that it delineates the regions of prominent jet flow features like the oscillating jet region, nonoscillating jet region, number of converging sections, and so on. Numerical predictions of the jet characteristics are obtained by modifying an existing nonswirling liquid jet model by including the swirling motion. The comparison between the experimental and numerical measurements shows that the pressure difference across the liquid sheet is important for the jet behavior and cannot be neglected in any theoretical analysis. (C) 2002 American Institute of Physics.

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This paper presents new experimental results on cryogenic jet flames formed by a coaxial injector at a pressure of 70 bar, which approaches the pressures found in rocket engines. This element, fed with liquid oxygen and gaseous hydrogen, is placed in a square combustion chamber equipped with quartz windows. The flame is examined via spectroscopy, OH* emission, and backlighting, the aim being to provide basic information on the flame structure. It is found that some of the OH* emission is absorbed by the OH radicals present in the flame. A detailed examination of this effect is presented, in which it is shown that, for this turbulent flame, the Abel transform gives the position of the intense reaction region, whether or not absorption is signficant. The flame is attached to the oxygen injector, as at low pressure. At high pressure, flame expansion is reduced compared with low pressure and is also less dependent on the momentum flux ratio between the hydrogen and the oxygen streams. An analysis of the relevant Damköhler numbers suggests that this is because the rate of combustion is mainly controlled by large-scale turbulent mixing at high pressure, and it is dominated by jet break-up, atomization, and vaporization at low pressures. Jet break-up is particularly dependent on the momentum flux ratio. Finally, the mean volumetric heat release rates and flame surface density in the experimental facility are estimated.

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The plug nozzle is one of the advanced expansion devices proposed to improve the overall performance of launcher liquid rocket engines. The present work investigates the three-dimensional flow field generated on this kind of nozzle by partitioning the primary nozzle into modules. A linear plug nozzle has been designed together with modules having two different geometries: a rectangular cross section and round-to-square module. Numerical simulations have been carried out considering the case where all modules of the primary nozzle are active and the case where one module is turned off. The solutions are compared and specific three-dimensional flow structures taking place inside the modules and on the plug are identified. The relationship between these structures and the skin friction distribution within the module and along the plug surface is investigated. Finally, the effect on performance of these three-dimensional flow features is emphasized. © 2006 Elsevier Masson SAS. All rights reserved.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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"The technique of modulation, or variable coefficients, is discussed and the analytical formulation is reviewed. Representative numerical results of the use of modulation are shown for the lifting and nonlifting cases. These results include the effects of modulation on peak acceleration, entry corridor, and heat absorption. Results are given for entry at satellite speed and escape speed. The indications are that coefficient modulation on a vehicle with good lifting capability offers the possibility of sizable loading reductions or, alternatively, wider corridors; thus, steep entries become practical from the loading standpoint. The amount of steepness depends on the acceptable heating penalty. The price of sizable fractions of the possible gains does not appear to be excessive."