Resumo em Inglês:

ABSTRACT: The research for low toxicity and no damage to the environment has stimulated the development of specific investigation lines in many areas. Inevitably, the criteria for safe handling, sensitivity and, above all, specific impulse (efficiencies) of propellant compositions are still superior in relation to ecological appeals. Nowadays, however, the solid or liquid propulsion, as aerospace as military, has already compounds to efficiency and eco-friendly characteristics. This study aimed at describing “green” alternatives to propulsive systems.

Resumo em Inglês:

ABSTRACT: The present work is primarily concerned with studying the effects of artificial dissipation and of certain diffusive terms in the turbulence model formulation on the capability of representing turbulent boundary layer flows. The flows of interest in the present case are assumed to be adequately represented by the compressible Reynolds-averaged Navier-Stokes equations, and the Spalart-Allmaras eddy viscosity model is used for turbulence closure. The equations are discretized in the context of a general purpose, density-based, unstructured grid finite volume method. Spatial discretization is based on the Steger-Warming flux vector splitting scheme and temporal discretization uses a backward Euler point-implicit integration. The work discusses in detail the theoretical and numerical formulations of the selected model. The computational studies consider the turbulent flow over a flat plate at 0.3 freestream Mach number. The paper demonstrates that the excessive artificial dissipation automatically generated by the original spatial discretization scheme can deteriorate boundary layer predictions. Moreover, the results also show that the inclusion of Spalart-Allmaras model cross-diffusion terms is primarily important in the viscous sublayer region of the boundary layer. Finally, the paper also demonstrates how the spatial discretization scheme can be selectively modified to correctly control the artificial dissipation such that the flow simulation tool remains robust for high-speed applications at the same time that it can accurately compute turbulent boundary layers.

Resumo em Inglês:

ABSTRACT This work presents a numerical analysis of the gas dynamic problem of localized and steady energy addition to uniform high-speed airflows. Firstly, the general effects caused by a localized energy deposition on the flow were investigated, then an extensive parametric analysis concerning the effects of energy deposition rate and dispersion for different free stream flow speeds was performed. As a general result, localized and steady energy deposition generates compression waves and constant property flow stream tube downstream to the source. The parametric analysis results have shown that either increasing the rate or decreasing dispersion in the orthogonal direction to the flow of the deposited energy has the effect of enhancing property flow changes, which is even more pronounced for lower flow speeds. In contrast, energy dispersion in the flow direction has presented very little effect on the flow changes. The results of this numerical analysis should be very helpful in studies of energy addition applications in hypersonic.

Resumo em Inglês:

ABSTRACT: A turbulent reacting flow in a channel with an obstacle was simulated computationally with large eddy simulation turbulence modeling and the Xi turbulent combustion model for premixed flame. The numerical model was implemented in the open source software OpenFoam. Both inert flow and reactive flow simulations were performed. In the inert flow, comparisons with velocity profile and recirculation vortex zone were performed as well as an analysis of the energy spectrum obtained numerically. The simulation with reacting flow considered a pre-mixture of propane (C 3 H 8) and air such that the equivalence ratio was equal to 0.65, with a theoretical adiabatic flame temperature of 1,800 K. The computational results were compared to experimental ones available in the literature. The equivalence ratio, inlet flow velocity, pressure, flame-holder shape and size, fuel type and turbulence intensity were taken from an experimental set up. The results shown in the present simulations are in good agreement with the experimental data.

Resumo em Inglês:

ABSTRACT: Concerns about the rising fuel price and environmental changes have led to the search for alternative fuels and energy sources. The interest in improving the performance of power generation, with the aim of reducing costs, increasing operating efficiency, and reducing the emissions of pollutants, has driven the scientific community to work on new burning technologies. Flameless combustion is one of the best alternative new technologies for a clean and efficient one. The burning of liquid fuels in power generation and propulsion systems depends on the effective atomization to increase the surface area of the fuel and thus to achieve high rates of mixing and evaporation. This work described the spray characteristics of hydrous ethanol in a blurry injector for applications in a flameless compact combustion chamber. The experimental results are obtained over a range of relatively low flow rates with different air-toliquid mass flow ratios.

Resumo em Inglês:

ABSTRACT: This paper addresses the subject of fiber optic chromatic dispersion effect on the performance of analog optical link with dual-drive electro-optic Mach-Zehnder modulator, aiming at aerospace applications. Thus, a direct detection link model that emphasizes both the modulator electronic drive and the dispersion characteristic of a linear optical fiber is discussed. Furthermore, a mathematical approach yielding a rather insightful analysis of the link performance for either optical double or single sideband modulation formats is fully discussed. It is worthwhile to point out that such modeling has the special feature of relying on a uniform nomenclature, which enables one to quickly retrieve a wide range of known results regarding optical fiber link performance that are already available on an ample literature. The model usefulness is illustrated by predicting the performance dependence of a direct detection fiber optic link with respect to the radiofrequency and link length. Results of numerical simulations for a link that comprises commercial optoelectronic components with potential for practical application on electronic warfare field were also provided.

Resumo em Inglês:

ABSTRACT: Autonomous star trackers are optical-electronic devices used for attitude determination of artificial satellites, having as a reference for this computation the positions of stars. There is one autonomous star tracker in development at the Aerospace Electronics Division of the Brazilian National Institute for Space Research. The autonomous star tracker imager is a complementary metal-oxide-semiconductor active pixel sensor, consisting of an integrated circuit with an array of them. Each pixel has a photodetector and an active amplifier. Since it has many amplifiers, the active pixel sensor has an additional fixed pattern noise, therefore its characterization is different from the traditional method used for the charge coupled devices. With this experiment, it was observed that the mean value per columns of fixed pattern noise is ~100% greater than the mean value of the pixel one. Taking into account this result, modeling the pixel fixed pattern noise will not be important to improve the autonomous star tracker sensibility. Furthermore, the random noise value was less than 1% of the fixed pattern noise range data, being possible to estimate it. In this work, we presented the fixed pattern noise new parametric model, which has a good agreement when compared with the experimental data. It was calculated Pearson’s product-moment correlation coefficient between the model and the observed data, in order to quantify the model accuracy and it was obtained 99% for flat field and 79% for dark current.

Resumo em Inglês:

ABSTRACT: The lead crack concept is adopted as the basis for a new fatigue lifeing method using the safe life philosophy. As part of its management strategy, a full-scale fatigue test is conducted to identify high-risk locations in the airframe, and for each item the time for retirement or structural repair is dictated by the safe life limit. A scatter factor is defined to account for the scatter in the material fatigue performance. The fatigue life variation of any given region of aircraft metallic structures is assumed to primarily correlate to the distribution of the equivalent pre-crack size of the fatigue crack initiators. By assuming that the sizes of these crack initiators are independent from each other, the present paper estimates the scatter factor by calculating safe life limit based on known growth characteristics of critical cracks.

Resumo em Inglês:

ABSTRACT: The toughening of polyamide 6 is desirable for many applications and may be obtained by adding a phase to the elastomeric matrix. However, this leads to a loss in its rigidity characteristics. Therefore, this study aimed at developing blends of polyamide 6/compound by recycled rubber (SBR-R), with the addition of compatibilizer graphitized polyethylene and polypropylene with maleic anhydride method by mixing in the molten state in order to obtain a balance between stiffness and toughness. The systems were prepared in several compositions, and their rheological properties and spectroscopy in the Fourier transform infrared were studied by means of rheological curves obtained in an internal mixer of Haake Buchler. The results obtained with the rheological study and Fourier transform infrared showed that mixtures of polyamide 6/graphitized polyethylene with maleic anhydride presented the best results compared to those of polyamide 6/ graphitized polypropylene with maleic anhydride, probably indicating reaction between the components. Thus, it was chosen graphitized polypropylene with maleic anhydride as a compatibilizing agent for carrying out other characterizations. Blends of polyamide 6/compound by recycled rubber/ graphitized polypropylene with maleic anhydride and their properties were analyzed by means of mechanical tests (tensile and impact), dynamic mechanical thermal analysis, differential scanning calorimetry, and scanning electron microscopy. The impact strength and elastic modulus of the blends compatibilized reduced somewhat when compared to polyamide 6. Therefore, these results indicate a good prospect of application of industrial waste, minimizing the negative effect on the environment and adding value to a disposable material.

Resumo em Inglês:

ABSTRACT: The aim of this study was to investigate the effects of hygrothermal exposure, ultraviolet (UV) radiation, salt spray and thermal shock aging on the thermomechanical behavior of glass fiber reinforced by poly (ether-imide) (PEI) composites. Dynamic mechanical (DMA) and Thermomechanical (TMA) analyses have been performed on the aged PEI composites after being submitted to the climatic chambers. Additional techniques have been used to characterize the laminates, such as optical microscopy and infrared spectroscopy (FT-IR) in order to evaluate possible structural changes in these materials. Slight changes were observed both in glass transition temperature and in thermal expansion coefficient as a result from the environmental conditioning used (hygrothermal, salt spray, UV radiation and thermal shock conditioning). Thus, when exposed to these conditions, PEI/glass fiber laminates maintain its compromise with the performance component.