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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 1,603 records · Page 89

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NASA NTRS1974

Fretting in aircraft turbine engines

Fretting usually produces both polished and pitted areas. Fretting occurs in connection with the relative motion between contacting surface elements. Particular attention is given to fretting in seals, splines, fans, compressors, and turbine blades. Recommended approaches to mitigate fretting problems include a reduction of the adhesion between two surfaces. Approaches for doing this may include the development of alloys which spontaneously generate a self-healing surface film, different in composition from the bulk alloy. Other fundamental adhesion studies have shown that surface crystal structure and crystallographic orientation significantly affect the adhesion properties of alloys.

Johnson, R. L.↗

NASA NTRS1975

Application of remote sensing technology to land evaluation, planning utilization of land resources, and assessment of wildlife areas in eastern South Dakota

A soils map for land evaluation in Potter County (Eastern South Dakota) was developed to demonstrate the use of remote sensing technology in the area of diverse parent materials and topography. General land use and soils maps have also been developed for land planning LANDSAT, RB-57 imagery, and USGS photographs are being evaluated for making soils and land use maps. LANDSAT fulfilled the requirements for general land use and a general soils map. RB-57 imagery supplemented by large scale black and white stereo coverage was required to provide the detail needed for the final soils map for land evaluation. Color infrared prints excelled black and white coverage for this soil mapping effort. An identification and classification key for wetland types in the Lake Dakota Plain was developed for June 1975 using color infrared imagery. Wetland types in the region are now being mapped via remote sensing techniques to provide a current inventory for development of mitigation measures.

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NASA NTRS1977

Thermal stress analysis of a graded zirconia/metal gas path seal system for aircraft gas turbine engines

A ceramic/metallic aircraft gas turbine outer gas path seal designed to enable improved engine performance is studied. Flexible numerical analysis schemes suitable for the determination of transient temperature profiles and thermal stress distributions in the seal are outlined. An estimation of the stresses to which a test seal is subjected during simulated engine deceleration from sea level takeoff to idle conditions is made. Experimental evidence has indicated that the surface layer of the seal is probably subjected to excessive tensile stresses during cyclic temperature loading. This assertion is supported by the analytical results presented. Brief consideration is given to means of mitigating this adverse stressing.

Taylor, C. M.↗

NASA NTRS1977

Inventory of wetland habitat using remote sensing for the proposed Oahe irrigation unit in eastern South Dakota

An inventory of wetlands for the area included in the proposed Oahe irrigation project was conducted to provide supplemental data for the wildlife mitigation plan. Interpretation techniques for inventoring small wetlands in the low relief terrain of the Lake Dakota Plain were documented and data summaries included. The data were stored and tabulated in a computerized spatial data analysis system.

Best, R. G.↗

NASA NTRS1977

Preliminary study of cyclic thermal shock resistance of plasma-sprayed zirconium oxide turbine outer air seal shrouds

Several experimental concepts representing potential high pressure turbine seal material systems were subjected to cyclic thermal shock exposures similar to those that might be encountered under severe engine start-up and shut-down sequences. All of the experimental concepts consisted of plasma-sprayed yttria stabilized ZrO2 on the high temperature side of the blade tip seal shroud. Between the ZrO2 and a cooled, dense metal backing, various intermediate layer concepts intended to mitigate thermal stresses were incorporated. Performance was judged on the basis of the number of thermal shock cycles required to cause loss of seal material through spallation. The most effective approach was to include a low modulus, sintered metal pad between the ZrO2 and the metallic backing. It was also found that reducing the density of the ZrO2 layer significantly improved the performance of specimens with plasma-sprayed metal/ceramic composite intermediate layers.

Bill, R. C.↗

NASA NTRS1978

Cold-air performance of free power turbine designed for 112-kilowatt automotive gas-turbine engine 3: Effect of stator vane end clearances on performance

An experimental investigation of a free power turbine designed for a 112-kW, automotive, gas turbine engine was made to determine the penalty in performance due to the stator vane end clearances. Tests were made over a range of mean section stator vane angles from 26 deg to 50 deg (as measured from the plane of rotation) with the vane end clearances filled. These results were compared with test results of the same turbine with vane end clearances open. At design equivalent values of rotative speed and pressure ratio and at a vane angle of 35 deg, the mass flow with the vane and clearances filled was about 8 percent lower than mass flow with vane end clearances open. The decrease in mass flow was mitigated by increasing the vane angle. With the vane end clearances filled, there was about a 66 percent reduction in mass flow when the vane angle was decreased from 40 deg to 26 deg. For the same decrease in vane angle the stator throat area decreased by about 50 percent. This result indicates that the rotor losses were increasing with decreasing vane angle.

Kofskey, M. G.↗

NASA NTRS1979

Solar Power Satellite (SPS) pilot beam and communication link subsystem investigation study, phase 1

A preliminary engineering model of ionospheric interactions with the pilot beam was established and used to demonstrate that the dual frequency baseline pilot beam system might not be viable in the presence of an unstable transmission path. Alternate approaches to remove this difficulty are described. Although ionospheric fluctuations will not significantly degrade beam pointing or raise the sidelobe levels, they will reduce transmission efficiency by upwards of 25%. Mitigating strategies to substantially reduce this effect are proposed. Based on the Klystron noise spectrum, the pilot beam transmitter power was determined as a function of frequency offset from the power beam carrier frequency. The RFI from the pilot beam, on the ground and at geosynchronous orbit is shown. Noise levels on the earth's surface due to the SPS are presented as a function of frequency and the number of SPS systems. Analysis of the communication subsystem indicates that a standard telemetry line of 1.544 MB/s would satisfy both voice and data link requirements. Additional links would be required for TV and radio transmissions.

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NASA NTRS1979

Potential for cogeneration of heat and electricity in California industry, phase 2

The nontechnical issues of industrial cogeneration for 12 California firms were analyzed under three categories of institutional settings: (1) industrial ownership without firm sales of power; (2) industrial ownership with firm sales of power; and (3) utility or third party ownership. Institutional issues were analyzed from the independent viewpoints of the primary parties of interest: the industrial firms, the electric utilities and the California Public utilities Commission. Air quality regulations and the agencies responsible for their promulgation were examined, and a life cycle costing model was used to evaluate the economic merits of representative conceptual cogeneration systems at these sites. Specific recommendations were made for mitigating measures and regulatory action relevant to industrial cogeneration in California.

Davis, H. S.↗

NASA NTRS1978

Super enrichments of Fe-group nuclei in solar flares and their association with large He-3 enrichments

Data on solar flares and perodic particle intensity enhancements in the energy range from 1 to 20 MeV/n are examined. It is found that: (1) Fe/He-4 ratios range from about 1 to 1000 times the solar ratio of 0.0004; (2) these high ratios mitigate against extended storage and large amounts of nuclear processing; (3) the CNO/He-4 ratio has a much smaller range of variability and a mean value of 0.02; (4) large He-3 and Fe enrichments are strongly associated, but not on a one-to-one basis; (5) large Fe enhancements sometimes occur without correspondingly large He-3 enrichments; and (6) none of the models so far advanced adequately explains the observed He-3 and heavy-nucleus enrichments.

Anglin, J. D.↗

NASA NTRS1978

The effects of copper and titanium on silicon solar cells

Copper-doped N/P silicon solar cells fabricated from the Czochralski grown single-crystal wafers were found to have good electrical characteristics, but the titanium-doped N/P silicon solar cells has considerably lower conversion efficiency. However, in the copper/titanium-doped solar cells, copper seems to mitigate the unfavorable effects of titanium. To explain this behavior, microstructural tests were performed on silicon wafers and solar cells doped with copper, titanium and copper/titanium. Dark forward and reverse I-V measurements were performed on the solar cells to correlate the microstructural defects with the p-n junction properties. It was found that copper precipitates were formed in the copper-doped and copper/titanium-doped wafers and cells. There was a significant voltage drop in the dark reverse I-V measurements of the titanium solar cells. Also, there were some electronically active defects in the depletion region of some titanium-doped cells. Reasons that lead to the above results are given in detail.

Salama, A. M.↗

NASA NTRS1980

Multistage depressed collector with efficiency of 90 to 94 percent for operation of a dual-mode traveling wave tube in the linear region

An axisymmetric, multistage, depressed collector of fixed geometric design was evaluated in conjunction with an octave bandwidth, dual mode traveling wave tube (TWT). The TWT was operated over a wide range of conditions to simulate different applications. The collector performance was optimized (within the constraint of fixed geometric design) over the range of TWT operating conditions covered. For operation of the TWT in the linear, low distortion range, 90 percent and greater collector efficiencies were obtained leading to TWT overall efficiencies of 20 to 35 percent, as compared with 2 to 5 percent with an undepressed collector. With collectors of this efficiency and minimized beam interception losses, it becomes practical to design dual mode TWT's such that the low mode can represent operation well below saturation. Consequently, the required pulse up in beam current can be reduced or eliminated, and this mitigates beam control and dual mode TWT circuit design problems. For operation of the dual mode TWT at saturation, average collector efficiencies in excess of 85 percent were obtained for both the low and high modes across an octave bandwidth, leading to a three to fourfold increase in the TWT overall efficiency.

Ramins, P.↗

NASA NTRS1980

Composite wall concept for high temperature turbine shrouds: Heat transfer analysis

A heat transfer analysis was made of a composite wall shroud consisting of a ceramic thermal barrier layer bonded to a porous metal layer which, in turn, is bonded to a metal base. The porous metal layer serves to mitigate the strain differences between the ceramic and the metal base. Various combinations of ceramic and porous metal layer thicknesses and of porous metal densities and thermal conductivities were investigated to determine the layer thicknesses required to maintain a limiting temperature in the porous metal layer. Analysis showed that the composite wall offered significant air cooling flow reductions compared to an all impingement air cooled, all metal shroud.

Stepka, F. S.↗

NASA NTRS1980

A methodology for the environmental assessment of advanced coal extraction systems

Procedures developed to identify and assess potential environment impacts of advanced mining technology as it moves from a generic concept to a more systems definition are described. Two levels of assessment are defined in terms of the design stage of the technology being evaluated. The first level of analysis is appropriate to a conceptual design. At this level it is assumed that each mining process has known and potential environmental impacts that are generic to each mining activity. By using this assumption, potential environmental impacts can be identified for new mining systems. When two or more systems have been assessed, they can be evaluated comparing potential environmental impacts. At the preliminary stage of design, a systems performance can be assessed again with more precision. At this level of systems definition, potential environmental impacts can be analyzed and their significane determined in a manner to facilitate comparisons between systems. At each level of analysis, suggestions calculated to help the designer mitigate potentially harmful impacts are provided.

Sullivan, P. J.↗

NASA NTRS1980

Possible existence and chemistry of ClO.O2 in the stratosphere

The influence of the existence and chemistry of the possible atmospheric constituent ClO.O2 on current models of stratospheric photochemistry is discussed. It is suggested that the formation of an asymmetric ClO.O2 complex may explain the observed suppression of the quantum yield in the chlorine-photosensitized decomposition of ozone in the presence of O2, and that the presence of the ClO.O2 formed may account for the current discrepancy between measurements and theoretical predictions of stratospheric ClO mixing ratio profiles. The presence of stratospheric ClO.O2 is also invoked as a possible mitigating influence on present estimates of ozone destruction due to chlorofluoromethane release.

Prasad, S. S.↗

NASA NTRS1980

Satellite Power System (SPS) laser studies. Volume 2: Meteorological effects on laser beam propagation and direct solar pumped lasers for the SPS

The primary emphasis of this research activity was to investigate the effect of the environment on laser power transmission/reception from space to ground. Potential mitigation techniques to minimize the environment effect by a judicious choice of laser operating parameters was investigated. Using these techniques, the availability of power at selected sites was determined using statistical meteorological data for each site.

Beverly, R. E., III↗

NASA NTRS1980

Coal gasification systems engineering and analysis, volume 2

The major design related features of each generic plant system were characterized in a catalog. Based on the catalog and requirements data, approximately 17 designs and cost estimates were developed for MBG and alternate products. A series of generic trade studies was conducted to support all of the design studies. A set of cost and programmatic analyses were conducted to supplement the designs. The cost methodology employed for the design and sensitivity studies was documented and implemented in a computer program. Plant design and construction schedules were developed for the K-T, Texaco, and B&W MBG plant designs. A generic work breakdown structure was prepared, based on the K-T design, to coincide with TVA's planned management approach. An extensive set of cost sensitivity analyses was completed for K-T, Texaco, and B&W design. Product price competitiveness was evaluated for MBG and the alternate products. A draft management policy and procedures manual was evaluated. A supporting technology development plan was developed to address high technology risk issues. The issues were identified and ranked in terms of importance and tractability, and a plan developed for obtaining data or developing technology required to mitigate the risk.

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NASA NTRS1981

A theoretical study of microwave beam absorption by a rectenna, introduction

The conditions required for a large rectenna array (i.e., reference design) to absorb nearly 100% of transmitted energy were studied. Design parameters including element spacing, and the manner in which these affect scatter were formulated. Amplitudes and directions of scatter and development of strategies for mitigation were also investigated. The effects on rectenna behavior of external factors such as weather and aircraft overflights were determined.

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NASA NTRS1981

Potential effects of the introduction of the discrete address beacon system data link on air/ground information transfer problems

This study of Aviation Safety Reporting System reports suggests that benefits should accure from implementation of discrete address beacon system data link. The phase enhanced terminal information system service is expected to provide better terminal information than present systems by improving currency and accuracy. In the exchange of air traffic control messages, discrete address insures that only the intended recipient receives and acts on a specific message. Visual displays and printer copy of messages should mitigate many of the reported problems associated with voice communications. The problems that remain unaffected include error in addressing the intended recipient and messages whose content is wrong but are otherwise correct as to format and reasonableness.

Grayson, R. L.↗