Search NASA⌕ Search

SEARCH · Search NASA

Results for “surface additives”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

An Exploratory Study of the Microstructure of Mullite Fibers

The microstructures of mullite composition fibers were examined by transmission electron microscopic techniques and by X-ray diffraction analyses. Both spun and monofilament fiber structures contained little porosity, nor did the degree of porosity change after heating the monofilament to 1205 C for one half hour. Thermal exposure produced crystallite growth and nucleation from the amorphous phase in all three of the spun fibers. After 116 hours at 1426 C, the crystallites of the standard spun fibers became contiguous. In addition, the surface crystallites of these fibers were found to be more than twice as large as the interior crystallites.

Santoro, G.↗
NASA NTRS1974

Comparison of theoretical and experimental boundary-layer development in a Mach 2.5 mixed-compression inlet

An analytical investigation was made of the boundary layer flow in an axisymmetric Mach 2.5 mixed compression inlet, and the results were compared with experimental measurements. The inlet tests were conducted in the Lewis 10- by 10-foot supersonic wind tunnel at a unit Reynolds number of 8.2 million/m. The inlet incorporated porous bleed regions for boundary layer control, and the effect of this bleed was taken into account in the analysis. The experimental boundary layer data were analyzed by using similarity laws from which the skin friction coefficient was obtained. The boundary layer analysis included predictions of laminar and turbulent boundary layer growth, transition, and the effects of the shock boundary layer interactions. In addition, the surface static pressures were compared with those obtained from an inviscid characteristics program. The results of investigation showed that the analytical techniques gave satisfactory predictions of the boundary layer flow except in regions that were badly distorted by the terminal shock.

Hingst, W. R.↗
NASA NTRS1974

Design, fabrication, and operation of a test rig for high-speed tapered-roller bearings

A tapered-roller bearing test machine was designed, fabricated and successfully operated at speeds to 20,000 rpm. Infinitely variable radial loads to 26,690 N (6,000 lbs.) and thrust loads to 53,380 N (12,000 lbs.) can be applied to test bearings. The machine instrumentation proved to have the accuracy and reliability required for parametric bearing performance testing and has the capability of monitoring all programmed test parameters at continuous operation during life testing. This system automatically shuts down a test if any important test parameter deviates from the programmed conditions, or if a bearing failure occurs. A lubrication system was developed as an integral part of the machine, capable of lubricating test bearings by external jets and by means of passages feeding through the spindle and bearing rings into the critical internal bearing surfaces. In addition, provisions were made for controlled oil cooling of inner and outer rings to effect the type of bearing thermal management that is required when testing at high speeds.

Signer, H. R.↗
NASA NTRS1975

Sikorsky interactive graphics surface design/manufacturing system

An interactive graphics system conceived to be used in the design, analysis, and manufacturing of aircraft components with free form surfaces was described. In addition to the basic surface definition and viewing capabilities inherent in such a system, numerous other features are present: surface editing, automated smoothing of control curves, variable milling patch boundary definitions, surface intersection definition and viewing, automatic creation of true offset surfaces, digitizer and drafting machine interfaces, and cutter path optimization. Documented costs and time savings of better than six to one are being realized with this system. The system was written in FORTRAN and GSP for use on IBM 2250 CRT's in conjunction with an IBM 370/158 computer.

Robbins, R.↗
NASA NTRS1976

An analytical study of reduced-gravity flow dynamics

Addition of surface tension forces to a marker-and-cell code and the performance of four incompressible fluid simulations in reduced gravity, were studied. This marker-and-cell code has a variable grid capability with arbitrary curved boundaries and time dependent acceleration fields. The surface tension logic includes a spline fit of surface marker particles as well as contact angle logic for straight and curved wall boundaries. Three types of flow motion were simulated with the improved code: impulsive settling in a model Centaur LH2 tank, continuous settling in a model and full scale Centaur LO2 tank and mixing in a Centaur LH2 tank. The impulsive settling case confirmed a drop tower analysis which indicated more orderly fluid collection flow patterns with this method providing a potential savings in settling propellants. In the LO2 tank, fluid collection and flow simulation into the thrust barrel were achieved. The mixing simulation produced good results indicating both the development of the flow field and fluid interface behavior.

Bradshaw, R. D.↗
NASA NTRS1976

Remote sensing of soil moisture

The surface emissivity and reflectivity of soil are strong functions of its moisture content. Changes in emissivity, observed by passive microwave techniques (radiometry), and changes in reflectivity, observed by active microwave techniques (radar), can provide information on the moisture content of the 0 to 5 cm surface layer. In addition, the thermal inertia of the surface layer, which can be remotely sensed by observing the diurnal range of surface temperature, is an indicator of soil moisture content. The thermal infrared approach to remote sensing of soil moisture has little utility in the presence of cloud cover, but provides soil moisture data at high spatial resolutions and thermal data which are a potentially useful indicator of crop status. Microwave techniques can penetrate cloud covers. The passive technique has been demonstrated by both aircraft and spacecraft instruments, but spatial resolution is limited by the size of the antenna which can be flown. Active microwave systems offer the possibility of better spatial resolution, but have yet to be demonstrated from aircraft or spacecraft platforms.

Schmugge, T.↗
NASA NTRS1978

Surface acoustic wave stabilized oscillators: Additional aging results

Updated aging data for SAW oscillators with aluminum transducers on ST-cut quartz, for gold transducers on ST-cut quartz, and for aluminum transducers on SiO2/LiTaO3. Devices with gold transducers age differently (both and shape of curve) from those having a aluminum transducers indicating the transducer metallization can represent an important aging mechanism.

Source record↗
NASA NTRS1977

High temperature environmental effects on metals

The current status of knowledge and ability to predict high-temperature environmental attack of metals is reviewed with particular reference to the gas turbine engine. Environmental attack is caused by high temperatures, combustion products, and impurities. A schematic representation of life-limiting factors of turbine components shows that environmental attack can lead to very early failures. Attention is given to high-temperature oxidation with prevailing modes of oxidation attack, and to hot corrosion and other impurity effects. Erosion attack results from the direct mechanical removal of component material by impact of hard substances like ash, sand, or dirt. Solutions to hot-corrosion problems can be found semiempirically by using improved alloys or ceramics, protective surface coatings, additives to the engine environment, and air/fuel cleanup to eliminate detrimental impurities.

Grisaffe, S. J.↗
NASA NTRS1978

Heat pipes in space and on earth

The performance of heat pipes used in the thermal control system of spacecraft such as OAO-III and ATS-6 is discussed, and applications of heat pipes to permafrost stabilization on the Alaska Pipeline and to heat recovery systems are described. Particular attention is given to the ATS-6, launched in 1974, which employs 55 heat pipes to carry solar and internal power loads to radiator surfaces. In addition, experiments involving radiative cooling based on cryogenic heat pipes have been planned for the Long Duration Exposure Facility spacecraft and for Spacelab. The role of heat pipes in Space Shuttle heat rejection services is also mentioned.

Ollendorf, S.↗
NASA NTRS1978

Interactive multi-mode blade impact analysis

The theoretical methodology used in developing an analysis for the response of turbine engine fan blades subjected to soft-body (bird) impacts is reported, and the computer program developed using this methodology as its basis is described. This computer program is an outgrowth of two programs that were previously developed for the purpose of studying problems of a similar nature (a 3-mode beam impact analysis and a multi-mode beam impact analysis). The present program utilizes an improved missile model that is interactively coupled with blade motion which is more consistent with actual observations. It takes into account local deformation at the impact area, blade camber effects, and the spreading of the impacted missile mass on the blade surface. In addition, it accommodates plate-type mode shapes. The analysis capability in this computer program represents a significant improvement in the development of the methodology for evaluating potential fan blade materials and designs with regard to foreign object impact resistance.

Alexander, A.↗
NASA NTRS1979

Fundamental mechanisms that influence the estimate of heat transfer to gas turbine blades

Estimates of the heat transfer from the gas to stationary (vanes) or rotating blades poses a major uncertainty due to the complexity of the heat transfer processes. The gas flow through these blade rows is three dimensional with complex secondary viscous flow patterns that interact with the endwalls and blade surfaces. In addition, upstream disturbances, stagnation flow, curvature effects, and flow acceleration complicate the thermal transport mechanisms in the boundary layers. Some of these fundamental heat transfer effects are discussed. The chief purpose of the discussion is to acquaint those in the heat transfer community, not directly involved in gas turbines, of the seriousness of the problem and to recommend some basic research that would improve the capability for predicting gas-side heat transfer on turbine blades and vanes.

Graham, R. W.↗
NASA NTRS1979

Fundamental mechanisms that influence the estimate of heat transfer to gas turbine blades

Heat tranfer problems in aircraft gas turbines required for improved prediction of turbine blade or vane gas-side heat transfer are examined. Estimates of the heat transfer from the gas to vanes or rotating blades are uncertain due to the complexity of the heat transfer processes, since the gas flow is three dimensional with complex secondary viscous flow patterns that interact with the endwalls and blade surfaces. In addition, upstream disturbances, stagnation flow, curvature effects, and flow acceleration complicate the thermal transport mechanisms in the boundary layers. The thermal state and flow characteristics of the hot gases that enter the turbine blade row, analytical methods for calculating the gas-side heat transfer to turbine blades, and flow phenomena such as stagnation, curvature effects, acceleration, secondary flows, and transition that influences local heat transfer rates are discussed.

Graham, R. W.↗
NASA NTRS1979

Field-aligned current sources in the high-latitude ionosphere

The paper determines the electric potential in a plane which is fed current from a pair of field-aligned current sheets. The ionospheric conductivity is modelled as a constant with an enhanced conductivity annular ring. It is shown that field-aligned current distributions are arbitrary functions of azimuth angle (MLT) and thus allow for asymmetric potential configurations over the pole cap. In addition, ionospheric surface currents are computed by means of stream functions. Finally, the discussion relates these methods to the electrical characteristics of the magnetosphere.

Barbosa, D. D.↗
NASA NTRS1980

Three dimensional spline-generated coordinate transformations for grids around wing-body configurations

A direct algebraic method was developed and applied to generate three dimensional grids around wing-body configurations. The method used is a generalized transfinite interpolation method which generates the desired coordinate transformation using geometric data only on the boundaries of the domain of interest. The geometric data that can be specified includes not only coordinates on the boundaries but also out-of-surface parametric derivatives that give a very precise control over the transformation in the vicinity of the surface. In addition to this, the method gives good control over the stretching of the mesh between different boundaries.

Eriksson, L. E.↗
NASA NTRS1981

Interactive multi-mode blade impact analysis

This paper describes the theoretical methodology used in developing an analysis for the response of turbine engine fan blades subjected to soft body (bird) impacts and the computer program that was developed using this methodology as its basis. This computer program is an outgrowth of two programs that were previously developed for the purpose of studying problems of a similar nature (a three-mode beam impact analysis and a multi-mode beam impact analysis). The present program utilizes an improved missile model that is interactively coupled with blade motion which is more consistent with actual observations. It takes into account local deformation at the impact area, blade camber effects, and the spreading of the impacted missile mass on the blade surface. In addition, it accommodates plate-type mode shapes. The analysis capability in this computer program represents a significant improvement in the development of the methodology for evaluating potential fan blade materials and designs with regard to foreign object impact resistance.

Alexander, A.↗
NASA NTRS1981

Genesis of recent silicic magmatism in the Medicine Lake Highland, California - Evidence from cognate inclusions found at Little Glass Mountain

Sparse, granular inclusions of early-formed minerals found within the Little Glass Mountain rhyolite flows in northern California are shown to provide a means of characterizing the physical conditions, at depth, beneath the Medicine Lake Highland during the latest phase of volcanic activity. Mineral compositions, in combination with thermodynamic calculations and experiments, suggest crystalization at a pressure of 5,200 bars within a 966-836 C temperature range; implying that mineral segregation and equilibration occurred at a depth of 15-18 km beneath the surface. In addition, mass balance calculations indicate that the Medicine Lake flow is a close approximation to the parental magma for the latest silicic lavas.

Mertzman, S. A.↗
NASA NTRS1981

Progress in radar snow research

Multifrequency measurements of the radar backscatter from snow-covered terrain were made at several sites in Brookings, South Dakota, during the month of March of 1979. The data are used to examine the response of the scattering coefficient to the following parameters: (1) snow surface roughness, (2) snow liquid water content, and (3) snow water equivalent. The results indicate that the scattering coefficient is insensitive to snow surface roughness if the snow is drv. For wet snow, however, surface roughness can have a strong influence on the magnitude of the scattering coefficient. These observations confirm the results predicted by a theoretical model that describes the snow as a volume of Rayleig scatterers, bounded by a Gaussian random surface. In addition, empirical models were developed to relate the scattering coefficient to snow liquid water content and the dependence of the scattering coefficient on water equivalent was evaluated for both wet and dry snow conditions.

Stiles, W. H.↗
NASA NTRS1982

Infrared emission spectrophotometric study of the changes produced by TiN coating of metal surfaces in an operating EHD contact

Infrared emission spectra and related measurements were obtained from an operating ball/plate elastohydrodynamic (EHD) sliding contact under a variety of operating conditions. In order to be able to compare the effect of the ball surface, some of the balls were coated with a thin layer of titanium nitride (TiN) by vapor deposition. Polyphenyl ether (5P4E) was used as lubricant and 1 percent of 1,1,2-trichloroethane (TCE) as a surface-probing additive. TiN is chemically inert and its thermal conductivity is lower than that of steel. Therefore, the overall temperatures with TiN coated balls were higher. Nevertheless, no scuffing was observed with the coated balls under conditions giving rise to scuffing with the uncoated balls. Tractions were lower with the TiN coated balls and always when TCE was added to the 5P4E. These findings were found to be inversely related to the degree of polarization of the spectral emission bands. The intensity and the dichrosim of these bands were related to shear rates and inlet conditions of the EHD contact.

Keller, L. E.↗