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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 91 records · Page 5

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NASA NTRS1980

Cold-air investigation of a 4 1/2 stage turbine with stage-loading factor of 4.66 and high specific work output. 2: Stage group performance

The stage group performance of a 4 1/2 stage turbine with an average stage loading factor of 4.66 and high specific work output was determined in cold air at design equivalent speed. The four stage turbine configuration produced design equivalent work output with an efficiency of 0.856; a barely discernible difference from the 0.855 obtained for the complete 4 1/2 stage turbine in a previous investigation. The turbine was designed and the procedure embodied the following design features: (1) controlled vortex flow, (2) tailored radial work distribution, and (3) control of the location of the boundary-layer transition point on the airfoil suction surface. The efficiency forecast for the 4 1/2 stage turbine was 0.886, and the value predicted using a reference method was 0.862. The stage group performance results were used to determine the individual stage efficiencies for the condition at which design 4 1/2 stage work output was obtained. The efficiencies of stages one and four were about 0.020 lower than the predicted value, that of stage two was 0.014 lower, and that of stage three was about equal to the predicted value. Thus all the stages operated reasonably close to their expected performance levels, and the overall (4 1/2 stage) performance was not degraded by any particularly inefficient component.

Whitney, W. J.↗

NASA NTRS1980

Shuttle orbiter Ku-band radar/communications system design evaluation. Ku band bent-pipe channel performance evaluation

Because of difficulties with the bit detector of the SPA mode 1 channel 3 input port, a new bit synchronizer was required. The two prime candidate designs are described and analyzed. The selected design is a modification of one which utilizes a phase frequency detector to track the received data clock frequency and a mid-bit transition point sample detector to generate a bit timing error (phase error) signal to control the relative phase between the local clock and the local data stream. The model used to calculate the effects of cable attenuation and rise time degradation is discussed.

Holmes, J. K.↗

NASA NTRS1982

Particle physics meets cosmology - The search for decaying neutrinos

The fundamental physical implications of the possible detection of massive neutrinos are discussed, with an emphasis on the Grand Unified Theories (GUTs) of matter. The Newtonian and general-relativistic pictures of the fundamental forces are compared, and the reduction of electromagnetic and weak forces to one force in the GUTs is explained. The cosmological consequences of the curved-spacetime gravitation concept are considered. Quarks, leptons, and neutrinos are characterized in a general treatment of elementary quantum mechanics. The universe is described in terms of quantized fields, the noninteractive 'particle' fields and the force fields, and cosmology becomes the study of the interaction of gravitation with the other fields, of the 'freezing out' of successive fields with the expansion and cooling of the universe. While the visible universe is the result of the clustering of the quark and electron fields, the distribution of the large number of quanta in neutrino field, like the mass of the neutrino, are unknown. Cosmological models which attribute anomalies in the observed motions of galaxies and stars to clusters or shells of massive neutrinos are shown to be consistent with a small but nonzero neutrino mass and a universe near the open/closed transition point, but direct detection of the presence of massive neutrinos by the UV emission of their decay is required to verify these hypotheses.

Henry, R. C.↗

NASA NTRS1983

Three-dimensional effects on airfoils

The effects of boundary layer flows along the walls of wind tunnels were studied to validate the transfer of two dimensional calculations to three dimensional transonic flowfield calculations. Results from trials in various wind tunnels were examind to determine the effects of the wall boundary flow on the control surfaces of an airfoil. Models sliding along a groove in the wall of a channel at sub- and transonic speeds were examined, with the finding that with either nonuniformities in the groove, or even if the channel walls are uniform, the lateral boundary layer can cause variations in the central flow region or alter the onset of shock at the transition point. Models for the effects in both turbulence and in the absence of turbulence are formulated, and it is noted that the characteristics of individual wind tunnels must be studied to quantify any existing three dimensional effects.

Chevallier, J. P.↗

NASA NTRS1984

Mach 6 flow-field and boundary-layer surveys beneath the forebody of an airbreathing missile

A wind tunnel investigation has been conducted to determine the flow characteristics of the shock layer beneath the forebody of a hypersonic, airbreathing missile incorporating an aft-mounted inlet. In the inviscid part of the flow field, the measured parameters were in agreement with those predicted by a three-dimensional Method of Characteristics theory. At test conditions matching full scale Mach and Reynolds numbers at an altitude for maximum L/D cruise, boundary layer transition occurred downstream of the inlet face. While this means that a full size vehicle would have a more easily separated boundary layer, it is noted that the Reynolds number discrepancy between wind tunnel and actual flight conditions may result in a movement of the transition point to somewhere upstream of the inlet.

Johnston, P. J.↗

NASA NTRS1984

Ionospheric electron density irregularities observed by satellite-to-satellite, dual-frequency, low-low Doppler tracking link

A low-low, satellite-to-satellite, dual-frequency, Doppler tracking experiment was performed. The data are analyzed here for irregularities in electron density at the altitude of 212 km. The differential Doppler data with the relative motion term removed are integrated to obtain a representation of the electron density variation along the satellite path. Well-known large-scale features such as the equatorial geomagnetic anomaly and day/night ionization level differences are clearly observed in the integrated data. The larger crest of the morning geomagnetic anomaly is seen to occur in the southern (winter) hemisphere in agreement with previous observations. In addition, a sharp peak in the electron density at the day-to-night transition point is observed in two consecutive revolutions. This effect may be due to the previously postulated atmospheric shock wave generated by supersonic motion of the terminator.

Estes, R. D.↗

NASA NTRS1984

A comparison of specularly reflected gyrating ion orbits with observed shock foot thicknesses

ISEE 1 and 2 flux gate magnetometer data has been used to measure the length or thickness of the 'foot' of 60 quasi-perpendicular supercritical bow shocks along the shock normal. These bow shock crossings are contrasted with 10 quasi-perpendicular subscritical shocks which do not exhibit the precursor foot. The extent of the foot structure is compared to the orbit of an ion having solar wind velocity and undergoing simple specular reflection about the shock normal. Good quantitative agreement between the measured value of the foot and the predicted value of about 0.7 ion gyroradii is evident. The foot thickness normalized to this predicted value is compared to the ratio of fast Mach number to critical fast Mach number. There is no dependence of the normalized foot thickness on Mach number other than at the transition point between subcritical and supercritical regimes. No dependence of the normalized foot thickness on upstream ion Beta is noted.

Livesey, W. A.↗

NASA NTRS1985

Combustor turbulence

The turbulence entering the turbine is produced in the combustor. High turbulence levels from the combustor can alter the location of the transition point on the turbine vane. The dynamics of turbulence and the progress being made in computing the flow are discussed.

Marek, C. J.↗

NASA NTRS1985

Where is the continuum in lattice quantum chromodynamics?

A Monte Carlo calculation of the quark-liberating phase transition in lattice quantum chromodynamics is presented. The transition temperature as a function of the lattice coupling g does not scale according to the perturbative beta function for 6/g-squared less than 6.1. Finite-size scaling is used in analyzing the properties of the lattice system near the transition point.

Kennedy, A. D.↗

NASA NTRS1986

Gallium-bearing sphalerite in a metal-sulfide nodule of the Qingzhen (EH3) chondrite

The composition and possible history of the Qingshen (EH3) chondrite is presented. The chondrite contains a population of spheroidal metal-sulfide nodules, which display textural evidence of reheating and melting. Evidence of metal sulfuration is also present, suggesting replacement of metal by sulfide during melting. This process has led to the nucleation of perryite along metal-sulfide interfaces. The Ga-bearing sphalerite that was found may have formed by injection of molten sulfide droplets into the metal followed by subsolidus diffusion of Ga from the metal into the sulfide. The latter may occur because of Ga supersaturation in the metal during progressive sulfuration and its decreased affinity for the metal phase during cooling below the taenite-kamacite transition point.

Rambaldi, E. R.↗

NASA NTRS1987

The right wing of the LEFT airplane

The NASA Leading-Edge Flight Test (LEFT) program addressed the environmental issues which were potential problems in the application of Laminar Flow Control (LFC) to transport aircraft. These included contamination of the LFC surface due to dirt, rain, insect remains, snow, and ice, in the critical leading-edge region. Douglas Aircraft Company designed and built a test article which was mounted on the right wing of the C-140 JetStar aircraft. The test article featured a retractable leading-edge high-lift shield for contamination protection and suction through perforations on the upper surface for LFC. Following a period of developmental flight testing, the aircraft entered simulated airline service, which included exposure to airborne insects, heavy rain, snow, and icing conditions both in the air and on the ground. During the roughly 3 years of flight testing, the test article has consistently demonstrated laminar flow in cruising flight. The experience with the LEFT experiment was summarized with emphasis on significant test findings. The following items were discussed: test article design and features; suction distribution; instrumentation and transition point reckoning; problems and fixes; system performance and maintenance requirements.

Powell, Arthur G.↗

NASA NTRS1990

Self-organized criticality in sandpiles - Nature of the critical phenomenon

The scaling behavior of sandpile models is investigated analytically. First, it is shown that sandpile models contain a set of domain walls, referred to as troughs, which bound regions that can experience avalanches. It is further shown that the dynamics of the troughs is governed by a simple set of rules involving birth, death, and coalescence events. A simple trough model is then introduced, and it is proved that the model has a phase transition with the density of the troughs as an order parameter and that, in the thermodynamic limit, the trough density goes to zero at the transition point. Finally, it is shown that the observed scaling behavior is a consequence of finite-size effects.

Carlson, J. M.↗

NASA NTRS1991

A numerical investigation of supersonic nozzle boundary layer transition

The boundary layer stability within the high-area-ratio nozzle at NASA Lewis was tested at five chamber pressure conditions. For all nozzle conditions examined, Taylor-Goertler vortices grew more rapidly than Tollmien-Schlichting waves. The experimental heat flux was accurately predicted by a laminar boundary layer computation, thereby confirming the laminar nature of the nozzle boundary layer flow. When the chamber pressure was increased in a series of cases, the transition point occurred farther upstream. The number of vortices contained in the dominant instability increased with chamber pressure.

Pauley, Laura L.↗

NASA NTRS1993

Advancements in the LEWICE Ice Accretion Model

Recent evidence has shown that the NASA/Lewis Ice Accretion Model, LEWICE, does not predict accurate ice shapes for certain glaze ice conditions. This paper will present the methodology used to make a first attempt at improving the ice accretion prediction in these regimes. Importance is given to the correlations for heat transfer coefficient and ice density, as well as runback flow, selection of the transition point, flow field resolution, and droplet trajectory models. Further improvements and refinement of these modules will be performed once tests in NASA's Icing Research Tunnel, scheduled for 1993, are completed.

Icing↗

NASA NTRS1993

Advancements in the LEWICE Ice Accretion Model

Wright, William B.↗

NASA NTRS1992

Transition of oscillatory flow in tubes - An empirical model for application to Stirling engines

Attention is given to an empirical model for transition to turbulence in oscillatory flows in straight tubes. Designed after a correlation for transition of a boundary layer on a flat plate, the model yields the laminar flow momentum thickness Reynolds number that must be met before transition to turbulence will occur. The transition point is located by comparing this to the actual momentum thickness Reynolds number. A scheme is proposed for estimating the momentum thickness Reynolds number in terms of the position within the cycle, the maximum value of the diameter Reynolds within the cycle, Re(max), and the dimensionless frequency, Valensi number. Results from an experimental study of oscillatory flow in a tube are employed to develop the model. When the flow is determined to be turbulent, it is proposed that a fully-developed, steady flow friction coefficient be applied. When the flow is laminar, the assumption of fully developed flow cannot be made; thus, a method is suggested for estimating the friction factor.

Simon, T. W.↗

NASA NTRS1993

Numerical modeling of crystal growth on a centrifuge for unstable natural convection configurations

The fluid mechanics associated with crystal growth processes on centrifuges is modeled using 2D and 3D models. Two-dimensional calculations show that flow bifurcations exist in such crystal growth configurations where the ampoule is oriented in the same direction as the resultant gravity vector and a temperature gradient is imposed on the melt. A scaling analysis is formulated to predict the flow transition point from the natural convection dominated regime to the Coriolis force dominated regime. Results of 3D calculations are presented for two thermal configurations of the crystal growth cell: top heated and bottom heated with respect to the centrifugal acceleration. In the top heated configuration, a substantial reduction in the convection intensity within the melt can be attained by centrifuge operations, and close to steady diffusion-limited thermal conditions can be achieved over a narrow range of the imposed microgravity level. In the bottom heated configuration the Coriolis force has a stabilizing effect on fluid motion by delaying the onset of unsteady convection.

Ramachandran, N.↗

NASA NTRS1957

Effect of bluntness on transition for a cone and a hollow cylinder at Mach 3.1

Bluntness was more effective in displacing transition downstream on a cylinder than on a cone. The downstream displacement of transition is related to the formation of a shock layer within which the Reynolds and Mach numbers are reduced and to pressure gradients that exist over the forward part of the model. Round bluntness in general had a favorable effect, whereas sharp-cornered flat bluntness above a certain size had unfavorable effects on the location of the transition point.

BODIES - SHAPE VARIABLES↗