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  • 1
    Publication Date: 2013-08-31
    Description: The results of an effort to assess the existing knowledge and plan the required experimentation in the area of turbine blade tip excitation forces is summarized. The work was carried out in three phases. The first was a literature search and evaluation, which served to highlight the state of the art and to expose the need for an articulated theoretical experimental effort to provide not only design data, but also a rational framework for their extrapolation to new configurations and regimes. The second phase was a start in this direction, in which several of the explicit or implicit assumptions contained in the usual formulations of the Alford force effect were removed and a rigorous linearized flow analysis of the behavior of a nonsymmetric actuator disc was carried out. In the third phase a preliminary design of a turbine test facility that would be used to measure both the excitation forces themselves and the flow patterns responsible for them were conducted and do so over a realistic range of dimensionless parameters.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: NASA-CR-171534 , NAS 1.26:171534
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  • 2
    Publication Date: 2013-08-31
    Description: This report documents progress to date in an ongoing study to analyze and model emissions leaving a proposed High Speed Civil Transport (HSCT) from when the exhaust gases leave the engine until they are deposited at atmospheric scales in the stratosphere. Estimates are given for the emissions, summarizing relevant earlier work (CIAP) and reviewing current propulsion research efforts. The chemical evolution and the mixing and vortical motion of the exhaust are analyzed to track the exhaust and its speciation as the emissions are mixed to atmospheric scales. The species tracked include those that could be heterogeneously reactive on the surfaces of the condensed solid water (ice) particles and on exhaust soot particle surfaces. Dispersion and reaction of chemical constituents in the far wake are studied with a Lagrangian air parcel model, in conjunction with a radiation code to calculate the net heating/cooling. Laboratory measurements of heterogeneous chemistry of aqueous sulfuric acid and nitric acid hydrates are also described. Results include the solubility of HCl in sulfuric acid which is a key parameter for modeling stratospheric processing. We also report initial results for condensation of nitric acid trihydrate from gas phase H2O and HNO3.
    Keywords: GEOPHYSICS
    Type: ARI-RR-902 , NASA-CR-189688 , NAS 1.26:189688
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  • 3
    Publication Date: 2013-08-31
    Description: Experimental and theoretical work done as Phase 3 of a program sponsored by MSFC to investigate the magnitude, origin, and parametric variations of destabilizing forces which arise in high power turbines due to blade-tip leakage effects are described. The two facilities which were built for this purpose are first described. The larger one is a closed, 2 atm pressurized Freon-12 flow loop in which is installed a 1:1 replica of the SSME first stage hydrogen turbine, which can be driven by the flow, and which generates about 14 KW of power into a load-absorbing DC generator. The smaller facility is used to measure the forces on labyrinth seals of the same type as those used in our turbine tests with a shrouded turbine. The seals can be kinematically whirled and spun (independently), and the inlet swirl can be set to a variety of values. Air is the working fluid (with atmospheric discharge) and the data are real-time pressure distributions in the seal glands. The five different unshrouded turbine configurations were tested with static offsets, plus one with a shroud band and a two-ridge seal. Theoretical models of various degrees of complexity were developed to help interpreting and extrapolating the data. The notion of partial work done by the fluid leaking through the tip gaps was put on a quantitative basis by examining the leakage vortex roll-up dynamics. This was used to obtain a theory of the work loss due to a uniform gap. Perturbation and multiple scale arguments were then used to extend this to the case of an eccentric turbine. This yields an unsteady, 3-D theory which can predict the distribution of the approach flow, and its effect on work defect, cross-forces, pressure patterns, and dynamic damping. The predictions agree qualitatively with the data and exhibit the correct trends, but the cross-forces are generally under-predicted.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: NAS 1.26:184341 , NASA-CR-184341
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  • 4
    Publication Date: 2018-12-01
    Description: The chemical evolution and mixing and vortical motion of a High Speed Civil Transport's engine exhausts must be analyzed in order to track the gas and its speciation as emissions are mixed to atmospheric scales. Attention is presently given to an analytic model of the wake dynamical processes which accounts for the roll-up of the trailing vorticity, its breakup due to the Crow instability, and the subsequent evolution and motion of the reconnected vorticity. The concentrated vorticity is noted to wrap up the buoyant exhaust and suppress its continued mixing and dilution. The species tracked encompass those which could be heterogeneously reactive on the surfaces of the condensed ice particles, and those capable of reacting with exhaust soot particle surfaces to form active contrail and/or cloud condensation nuclei.
    Keywords: ENVIRONMENT POLLUTION
    Type: AIAA PAPER 91-3158
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  • 5
    Publication Date: 2016-06-07
    Description: Calculations are performed to determine the dynamic effects of mechanical power transmission from the nacelle of a horizontal axis wind machine to the ground or to an intermediate level. It is found that resonances are likely at 2 or 4/REV, but they occur at low power only, and seem easily correctable. Large reductions are found in the harmonic torque inputs to the generator at powers near rated.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Res. Center Wind Turbine Structural Dyn.; p 187-193
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  • 6
    Publication Date: 2017-07-04
    Type: paper
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  • 7
    Publication Date: 2011-08-24
    Description: No abstract available
    Keywords: Man/System Technology and Life Support
    Type: Gravitational and space biology bulletin : publication of the American Society for Gravitational and Space Biology (ISSN 1089-988X); Volume 18; 2; 93-4
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  • 8
    Publication Date: 2016-06-07
    Description: The development of a linear model for the prediction of labyrinth seal forces and on its comparison to available stiffness data is presented. A discussion of the relevance of fluid damping forces and the preliminary stages of a program to obtain data on these forces are examined. Fluid-dynamic forces arising from nonuniform pressure patterns in labyrinth seal glands are known to be potentially destablizing in high power turbomachinery. A well documented case in point is that of the space Shuttle Main Engine turbopumps. Seal forces are also an important factor for the stability of shrouded turbines, acting in that case in conjunction with the effects of blade-tip clearance variations.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Lewis Research Center Rotordynamic Instability Problems in High-Performance Turbomachinery; p 235-256
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  • 9
    Publication Date: 2014-09-24
    Description: As part of a study into turbine blade tip destabilizing forces, a seals test rig was built in which spin rate, circular whirl rate, direction and amplitude of inlet swirl angle, and eccentricity can all be controlled over wide ranges, and measurements can be made at gap Reynolds numbers up to about 2 x 10(exp 4). This facility is described and preliminary data is presented for a one cavity labyrinth seal with a flat, stator mounted land. The impact of different flow coefficients for the first and second knives on the rotordynamic coefficients was found. While this effect is dominant for the direct forces, it should also be incorporated into calculations of cross forces where it has an impact under many conditions.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Lewis Research Center, Rotordynamic Instability Problems in High-Performance Turbomachinery, 1990; p 135-146
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  • 10
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    In:  Other Sources
    Publication Date: 2011-08-18
    Description: A previously reported bias in the right ascension residuals of astrolabe observations of Mars is removed by correcting for equinox motion and relating the observations to the Jet Propulsion Laboratory's planetary ephemeris, DE111. The remaining residuals show a 'phase effect', the magnitude of which is solved for and compared with that previously found for meridian transit observations. The final residuals reveal no significant offset in either right ascension or declination. In modifying the residuals, use is also made of Fricke's (1980) correction for the motion of the FK 4 equinox.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astronomy and Astrophysics; 102; 3, Oc; Oct. 198
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