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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Progress in Protective Coatings for Aircraft Gas Turbines: A Review of NASA Sponsored Research

Problems associated with protective coatings for advanced aircraft gas turbines are reviewed. Metallic coatings for preventing titanium fires in compressors are identified. Coatings for turbine section are also considered, Ductile aluminide coatings for protecting internal turbine-blade cooling passage surface are also identified. Composite modified external overlay MCrAlY coatings deposited by low-pressure plasma spraying are found to be better in surface protection capability than vapor deposited MCrAlY coatings. Thermal barrier coating (TBC), studies are presented. The design of a turbine airfoil is integrated with a TBC, and computer-aided manufacturing technology is applied.

Merutka, J. P.↗
NASA NTRS1981

The atmosphere of Jupiter - An analysis of the Voyager radio occultation measurements

Coherently related S and X band signals of 2.3 and 8.4 GHz, respectively, which were transmitted from Voyagers 1 and 2 were used to probe the Jovian atmosphere. Height profiles of the gas refractivity, molecular number density, pressure, temperature, and microwave absorption in the troposphere and stratosphere were observed at latitudes ranging from 0 to 70 deg S. At 1000 mbar, the temperature was + or - 5 K and the lapse rate was equal to the adiabatic value of 2.1 K/km within the resolution of the measurements. The ammonia abundance in this region was 0.022 + or - 0.008%, which is in good agreement with values derived from cosmic abundance considerations. The tropopause at the 140 mbar level had a temperature of 110 K, which increased with increasing altitude, reaching 160 + or - 20 K in the 10 to 1 mbar region. Significant horizontal density variations were detected in the stratosphere, which implies a nonuniform temperature and aerosol distribution across the Jovian disk or across high- and low-pressure regions due to local atmospheric dynamics.

Lindal, G. F.↗
NASA NTRS1980

Classification, experimental petrology and possible volcanic histories of the Apollo 11 high-K basalts

The Apollo 11 high-K basalt samples are classified into three textural categories: vitrophyric, anti-insertal, and antiophitic. Low-pressure phase equilibrium experiments and cooling rate studies were performed on a synthetic analog of 10085, 832. The dynamic crystallization experiments were designed to study textural development with: (1) a variable cooling rate from a constant initial temperature above the liquidus, and (2) cooling at a constant rate from variable initial temperatures below the liquidus. These experiments show that a variety of cooling rates initiated from temperatures both below and above the liquidus can produce all the observed textures. The results are consistent with the interpretation that all of the high-K basalt samples were derived from a single lava flow or lava lake.

Grove, T. L.↗
NASA NTRS1982

Measurement of cardiopulmonary performance during acute exposure to a 2440-m equivalent atmosphere

Each of 20 subjects (ranging in age from 18 to 38 years, 15 being male, five female) was given two Bruce Protocol symptom-limited maximum treadmill stress tests, breathing sea-level compressed air (20.9% O2) for one test and a 2440-m equivalent (15.5% O2) for the other. A significant difference was found to exist between measured VO2 max (p less than 0.0002) and exercise time (p less than 0.0004) for the two conditions. No significant differences were observed in heart rate or the recovery time to a respiratory quotient of less than 1. Hemoglobin saturation, as measured by an ear oximeter, averaged 95% for sea-level and 91% for the 2440-m equivalent gases. These results support a 2440-m equivalent contingency atmosphere in the Space Shuttle prior to donning a low-pressure suit for the purpose reducing nitrogen washout times.

Levitan, B. M.↗
NASA NTRS1981

Evaluation of Nimbus 7 SMMR sensor with airborne radiometers and surface observations in the Norwegian Sea

Measurements made by the Nimbus 7 SMMR are compared with near simultaneous observations using the airborne SMMR simulator and with surface observations. The area of the test is in the Norwegian Sea between Bear Island and Northern Norway. It is noted that during the observation period two low-pressure systems were located in the test area, giving a spatial wind variation from 3-20 m/s. It is shown that the use of the currently available brightness temperatures and algorithms for SMMR does not give universally satisfactory results for SST and wind speed under extreme weather conditions. In addition, the SMMR simulator results are seen as indicating the need for more work on calibration.

Gloersen, P.↗
NASA NTRS1983

Pyroxene whiskers and platelets in interplanetary dust - Evidence of vapour phase growth

Enstatite crystals with whisker and platelet morphologies have been observed within chondritic porous micrometeorites. Samples of such crystals collected from the stratosphere are described. The samples display unique crystal morphologies and microstructures, such as axial screw dislocations, that strongly suggest that they are primary vapor phase condensates which could have formed either in the solar nebula or in presolar environments. The relationship between the crystal polymorphism and the thermal conditions of growth is discussed, adopting the view that protoenstatite and orthoenstatite are the stable high and low temperature forms, respectively. The kinetic aspects and mechanisms of whisker and platelet growth are considered, and the nature of the likely growth medium for the crystals is addressed. It is concluded that growth from a relatively low-pressure vapor phase is the most likely mode of growth.

Bradley, J. P.↗
NASA NTRS1982

Top-off procedure for space-bound superfluid helium cryostats

Tests have been carried out on the transfer of pressurized liquid helium, slightly above the lambda temperature, in order to determine the optimum transfer parameters for a ground-based top-off just prior to launch. It is shown that the maximum mass fill of a spaceborne cryostat can be accomplished with the low-pressure top-off after initial fill with normal helium. The realistic maximum fill at temperatures below the lambda temperature can be expected to be at least 90 percent, which results in about 40 to 50 percent more mass at launch than without the top-off. In each case, specific ground support equipment is required to satisfy the individual cryostat requirements and extreme care is necessary during the transfer procedure.

Petrac, D.↗
NASA NTRS1984

Analytical fuel property effects: Small combustors

The study performed in Phase 1 of this program applies only to a T700/CT7 engine family type combustor functioning in the engine as defined and does not necessarily apply to other cycles or combustors of differing stoichiometry. The study was not extended to any of the fuel delivery accessories such as pumps or control systems, nor was there any investigation of potential systems problems which might arise as a consequence of abnormal properties such as density which might affect delivery schedules or aromatics content which might affect fuel system seals. The T700/CT7 engine is a front drive turboshaft or turboprop engine in the 1500-1800 shp (1120-1340 kW) class as currently configured with highpower core flows of about 10 lb/sec (4.5 kg/sec). It employs a straight-through annular combustion system less than 5 in. (12.5 cm) in length utilizing a machined ring film cooled construction and twelve low-pressure air blast fuel injectors. Commercial and Naval versions employ two 0.5 Joule capacitive discharge surface gap ignitors.

Cohen, J. D.↗
NASA NTRS1983

The stability of coronal loops - Finite-length and pressure-profile limits

Results are described from a quickly converging, necessary-and-sufficient, MHD-stability test for coronal-loop models. The primary stabilizing influence arises from magnetic line tying at the photosphere, and this end conditions requires a series expansion of possible loop excitations. The stability boundary is shown to quickly approach a limit as the number of terms increases, providing a critical length for the loop in proportion to its transverse magnetic scale. Several models of force-free-field profiles are tested and the stability behavior of a localized current channel, embedded in an external current-free region, is shown to be superior to that of other, broader, current profiles. Pressure-gradient effects, leading to increased or decreased stability, are shown to be amplified by line tying. Long loops must either conduct low net current, or exhibit an axial-field reversal coexisting with a low-pressure core. The limits on stability depend on the magnetic aspect ratio, the plasma-to-magnetic pressure ratio, and the field orientation at the loop edge. Applications of these results to the structure of coronal loops are described.

Einaudi, G.↗
NASA NTRS1984

Simulation of blunt-fin-induced shock wave and turbulent boundary-layer interaction

A supersonic flow over a blunt fin mounted on a flat plate is numerically simulated. The fin shock causes the boundary layer to separate and results in a complicated, three-dimensional shockwave and boundary-layer interaction. The computed result is in good agreement with the measured pressure on the fin and the flat plate. The main features, such as peak pressure on the fin leading edge and a double peak pressure on the plate, are closely predicted. The role of the horseshoe vortex is discussed. The vortex leads to the development of high-speed flow, and, hence, low-pressure regions on the fin and the plate. Different thicknesses of the incoming boundary layer have been studied. Varying the thicknesses by an order of magnitude shows that the size of the horseshoe vortex and therefore the spatial extent of the interaction are inviscid-dominated, and are weakly dependent on the Reynolds number. Colored graphics are used to show details of the interaction flow field.

Hung, C.-M.↗
NASA NTRS1983

Design analysis of Rayleigh-step floating-ring seals

The analysis and design of a 50-mm diameter floating-ring helium buffer seal are described. The seal rings incorporated Rayleigh-step lift pads to provide hydrodynamic forces to separate the rings from the shaft. Maximum surface speed is 183 m/s (600 fps) and maximum buffer gas pressure is 1389 kPa (200 psia). An operating range map was computed as a function of speed and pressure. Contradictory problems arise due to excessive friction preventing ring tracking at low-speed, high-pressure conditions and insufficent friction to retard inertia driven motions at high-speed, low-pressure conditions. Steady-state and dynamic analyses and performance are described, as well as the results of thermal studies.

Artiles, A.↗
NASA NTRS1983

Phenomenological in-situ TEM gas exposure studies of palladium particles on MgO at room temperature

It has been found that very small vapor-deposited catalytically active metal particles in the 1-2 nm size range on metal oxide substrates can undergo significant changes when they are exposed to gases such as oxygen or air, or even when allowed to 'anneal' at room temperature (RT) under vacuum conditions. The present investigation is concerned with continued in-situ gas exposures of as-deposited, 1 to 2 nm size palladium particles on MgO to air, oxygen, nitrogen, hydrogen, CO, and water vapor at RT. It is found that the low-pressure exposure to various gases at RT can significantly affect small palladium particles supported on MgO surfaces. Exposure to oxygen for 3 min at 0.0002 m bar produces a considerable amount of coalescence, flattening of the particles, and some distinct crystallographic particle shapes.

Heinemann, K.↗
NASA NTRS1983

Homogeneous processes of atmospheric interest

Upper atmospheric research programs in the department of chemical kinetics are reported. Topics discussed include: (1) third-order rate constants of atmospheric importance; (2) a computational study of the HO2 + HO2 and DO2 + DO2 reactions; (3) measurement and estimation of rate constants for modeling reactive systems; (4) kinetics and thermodynamics of ion-molecule association reactions; (5) entropy barriers in ion-molecule reactions; (6) reaction rate constant for OH + HOONO2 yields products over the temperature range 246 to 324 K; (7) very low-pressure photolysis of tert-bytyl nitrite at 248 nm; (8) summary of preliminary data for the photolysis of C1ONO2 and N2O5 at 285 nm; and (9) heterogeneous reaction of N2O5 and H2O.

Rossi, M. J.↗
NASA NTRS1983

Deposition of silicon nitride from SiCl4 and NH3 in a low pressure RF plasma

Silicon nitride coatings were deposited in a low-pressure (1-10 Torr) RF plasma from SiCl4 and NH3 in the presence of argon onto stainless martensitic steel grounded and floating substrates at 300 C and 440 C respectively. The heating of the substrates depends mainly on the position and the induced RF power. The coatings were identified as silicon nitride by X-ray investigation and were found to contain chlorine by energy-dispersive analysis of X-rays. The growth rate, the microhardness and the chlorine concentration of the coatings were determined as a function of the total gas pressure, the RF power input and the NH3-to-SiCl4 ratio. It was observed that the coatings on the floating substrates have higher deposition rates and are of superior quality.

Ron, Y.↗
NASA NTRS1984

Thermal barrier coating life prediction model development

Thermal barrier coatings (TBCs) for turbine airfoils in high-performance engines represent an advanced materials technology that has both performance and durability benefits. In order to achieve these benefits, however, the TBC system must be reliable. Prediction of the lives of two types of strain-tolerant and oxidation-resistant TBC systems that are produced by commercial coating suppliers to the gas turbine industry is examined. The plasma sprayed TBC system, composed of a low-pressure plasma spray (LPPS) applied oxidation resistant NiCrAlY bond coating and an air-plasma-sprayed yttria (8 percent) partially stabilized zirconia insulative layer is applied by both Chromalloy and Klock. The second type of TBC is applied by the electron beam-physical vapor depositon (EB-PVD) process by Temescal.

Strangman, T. E.↗
NASA NTRS1957

Nonmetallic Material Compatibility with Liquid Fluorine

Static tests were made on the compatibility of liquid fluorine with several nonmetallic materials at -3200 F and at pressures of 0 and 1500 pounds per square inch gage. The results are compared with those from previous work with gaseous fluorine at the same pressures, but at atmospheric temperature. In general, although environmental effects were not always consistent, reactivity was least with the low-temperature, low-pressure liquid fluorine. Reactivity was greatest with the warm, high-pressure gaseous fluorine. None of the liquids and greases tested was found to be entirely suitable for use in fluorine systems. Polytrifluorochloroethylene and N-43, the formula for which is (C4F9)3N, did not react with liquid fluorine at atmospheric pressure or 1500 pounds per square inch gage under static conditions, but they did react when injected into liquid fluorine at 1500 pounds per square inch gage; they also reacted with gaseous fluorine at 1500 pounds per square inch gage. While water did not react with liquid fluorine at 1500 pounds per square inch gage, it is known to react violently with fluorine under other conditions. The pipe-thread lubricant Q-Seal did not react with liquid fluorine, but did react with gaseous fluorine at 1500 pounds per square inch gage. Of the solids, ruby (Al2O3) and Teflon did not react under the test conditions. The results show that the compatibility of fluorine with nonmetals depends on the state of the fluorine and the system design.

Price, Harold G , Jr↗
NASA NTRS1926

Experimental investigation of the physical properties of medium and heavy oils, their vaporization and use in explosion engines. Part I

While little has been accomplished in obtaining an abundant supply of light oils from coal and heavy oils, progress has been made on engine design to make use of the heavier oils. Progress has been made in two different directions which are outlined in this paper: the group of engines with medium and high-pressure carburetion in the cylinder; and the group of engines with low-pressure carburetion of the heavy oils before reaching the cylinder.

OILS↗
NASA NTRS1940

Stability of Castering Wheels for Aircraft Landing Gears

A theoretical study was made of the shimmy of castering wheels. The theory is based on the discovery of a phenomenon called kinematic shimmy. Experimental checks, use being made of a model having low-pressure tires, are reported and the applicability of the results to full scale is discussed. Theoretical methods of estimating the spindle viscous damping and the spindle solid friction necessary to avoid shimmy are given. A new method of avoiding shimmy -- lateral freedom -- is introduced.

Kantrowitz, Arthur↗