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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 451 records · Page 25
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NASA NTRS1979

International planetary patrol observations of Saturn's rings. II - Four color phase curves and their analysis

New phase curves for Saturn's rings at an intermediate tilt angle B of about 17 deg are presented. Quantitative results for each of the A and B rings are reported in terms of the opposition effect, phase coefficient, and best logarithmic fit to the phase curve. There was no significant difference between the shape of the phase curves for the two rings in each of the four colors, and a four-parameter multiple scattering model of the rings was consistent with the observations. In this model, the difference in the phase curves for different colors can be explained by a variation in the single scattering albedo with wavelength. The observations allow the particles to have the same composition in the A and B rings, so that their different photometric behavior is explained by differences in optical depth and volume density in the two rings.

Esposito, L. W.↗
NASA NTRS1979

First results of a study on turbulent boundary layers in oscillating flow with a mean adverse pressure gradient

The development of a turbulent unsteady boundary layer with a mean pressure gradient strong enough to induce separation, in order to complete the extend results obtained for the flat plate configuration is presented. The longitudinal component of the velocity is measured using constant temperature hot wire anemometer. The region where negative velocities exist is investigated with a laser Doppler velocimeter system with BRAGG cells. The boundary layer responds by forced pulsation to the perturbation of potential flow. The unsteady effects observed are very important. The average location of the zero skin friction point moves periodically at the perturbation frequency. Average velocity profiles from different instants in the cycle are compared. The existence of a logarithmic region enables a simple calculation of the maximum phase shift of the velocity in the boundary layer. An attempt of calculation by an integral method of boundary layer development is presented, up to the point where reverse flow starts appearing.

Houdeville, R.↗
NASA NTRS1980

Asynchronous vibration problem of centrifugal compressor

An unstable asynchronous vibration problem in a high pressure centrifugal compressor and the remedial actions against it are described. Asynchronous vibration of the compressor took place when the discharge pressure (Pd) was increased, after the rotor was already at full speed. The typical spectral data of the shaft vibration indicate that as the pressure Pd increases, pre-unstable vibration appears and becomes larger, and large unstable asynchronous vibration occurs suddenly (Pd = 5.49MPa). A computer program was used which calculated the logarithmic decrement and the damped natural frequency of the rotor bearing systems. The analysis of the log-decrement is concluded to be effective in preventing unstable vibration in both the design stage and remedial actions.

Fujikawa, T.↗
NASA NTRS1980

Effect of fluid forces on rotor stability of centrifugal compressors and pumps

A simple two dimensional model for calculating the rotordynamic effects of the impeller force in centrifugal compressors and pumps is presented. It is based on potential flow theory with singularities. Equivalent stiffness and damping coefficients are calculated for a machine with a vaneless volute formed as a logarithmic spiral. It is shown that for certain operating conditions, the impeller force has a destablizing effect on the rotor.

Colding-Jorgensen, J.↗
NASA NTRS1979

Solar cycle variations in IMF intensity

Annual averages of logarithms of hourly interplanetary magnetic field (IMF) intensities, obtained from geocentric spacecraft between November 1963 and December 1977, reveal the following solar cycle variation. For 2-3 years at each solar minimum period, the IMF intensity is depressed by 10-15% relative to its mean value realized during a broad 9-year period centered at solar maximum. No systematic variations occur during this 9-year period. The solar minimum decrease, although small in relation to variations in some other solar wind parameters, is both statistically and physically significant.

King, J. H.↗
NASA NTRS1979

Pioneer-Venus solar flux radiometer

The paper presents the design and performance characteristics of the Solar Flux Radiometer flown on the Large Probe of the Pioneer-Venus Multiprobe spacecraft. Radiance measurements of the Venusian atmosphere in spectral channels between 400 and 1800 nm as a function of altitude were made, along with elevation and azimuthal measurements of the radiation field performed with five optical channels. Filtered Si and Ge photovoltaic detector output currents were processed with logarithmic transimpedance converters prior to being multiplexed and digitized. Atmospheric sampling in elevation and azimuth was done according to a Gaussian integration scheme; the received data were used to determine the deposition of solar energy in the Venus atmosphere along with upward and downward fluxes and radiances with an altitude resolution of several hundred meters between 67 km and the surface.

Palmer, J. M.↗
NASA NTRS1979

Asteroid taxonomy and the distribution of the compositional types

Physical observations of minor planets documented in the TRIAD computer file are used to classify 752 objects into the broad compositional types C, S, M, E, R, and U (unclassifiable) according to the prescriptions adopted by Bowell et al. (1978). Diameters are computed from the photometric magnitude using radiometric and/or polarimetric data where available, or else from albedos characteristic of the indicated type. An analysis of the observational selection effects leads to tabulation of the actual number of asteroids, as a function of type and diameter, in each of 15 orbital element zones. For the whole main belt the population is 75% of type C, 15% of type S, and 10% of other types, with no belt-wide dependence of the mixing ratios on diameter. In some zones the logarithmic diameter-frequency relations are decidedly nonlinear. The relative frequency of S-type objects decreases smoothly outward through the main belt, with exponential scale length 0.5 AU. The rarer types show a more chaotic, but generally flatter, distribution over distance. Characteristic type distributions, contrasting with the background population, are found for the Eos, Koronis, Nysa and Themis families.

Zellner, B.↗
NASA NTRS1980

Pioneer Venus Sounder Probe Solar Flux Radiometer

The Solar Flux Radiometer aboard the Pioneer Venus Sounder Probe operated successfully during its descent through the atmosphere of Venus. The instrument measured atmospheric radiance over the spectral range from 400 to 1800 nm as a function of altitude. Elevation and azimuthal measurements on the radiation field were made with five optical channels. Twelve filtered Si and Ge photovoltaic detectors were maintained near 30 C with a phase-change material. The detector output currents were processed with logarithmic transimpedance converters and digitized with an 11-bit A/D converter. Atmospheric sampling in both elevation and azimuth was done according to a Gaussian integration scheme. The serial output data averaged 20 bits/sec, including housekeeping (sync, spin period, sample timing and mode). The data were used to determine the deposition of solar energy in the atmosphere of Venus between 67 km and the surface along with upward and downward fluxes and radiances with an altitude resolution of several hundred meters. The results allow for more accurate modeling of the radiation balance of the atmosphere than previously possible.

Tomasko, M. G.↗
NASA NTRS1980

Preliminary measurements of aerodynamic damping of a transonic compressor rotor

The aeroelastic behavior of a transonic compressor rotor operated in the MIT Blowdown Compressor Facility has been examined by means of piezoelectric motion sensors at the base of each of the 23 blades. Excitation has been observed due to rotating stall, due to an incipient flutter, and due to the facility startup transient. A method has been found for determining the aerodynamic damping force by modal analysis of the blade motion. Application of this technique to the example of excitation by rotating stall has led to the conclusions that the blade loading decreases in the stall cell, and that the damping force on the blades in the clean flow is in phase with blade velocity but opposite it in sign, leading to a logarithmic decrement of 0.2. This method of force derivation has quite general applicability as it requires only blade motion data such as are routinely acquired with strain gages. It is argued that models are needed for aerodynamic damping which focus on the effects of near neighbors of a given blade, since flutter often results in large response of isolated blades or small groups of blades.

Crawley, E. F.↗
NASA NTRS1980

On the stability of three-dimensional compressible nonparallel boundary layers

A compressible linear stability theory is presented for three-dimensional nonuniform boundary layers. The amplitude, phase, and wavenumber equations which govern the motion of the disturbance are obtained by using the method of multiple scales. Group velocity trajectories are used to identify the disturbance growth direction. The spatial stability theory is applied to the flow on a laminar flow control supercritical sweptback wing of infinite span. Three different methods are used to calculate the absolute maximum logarithmic amplitude ratio N. In the front crossflow instability region, the method of maximum spatial growth rate predicts large difference in N compared with the method of fixed wavelength and the method of fixed spanwise component of wavelength. This difference decreases in the middle streamwise instability region, and almost vanishes in the rear crossflow instability region. Compressibility of the medium reduces N by about 15% in both the front and rear regions, and by about 40% in the middle region of the wing. Nonuniformity of the medium has large effects specially in the rear region.

El-Hady, N. M.↗
NASA NTRS1982

Log-Output Signal Processor Scans Eight Decades

Processor has automatic range switching and continuous readout over eight decades. Comparator output switches logarithmic converter to detector of interest and enables blinder grid to protect more-sensitive detector when operating in high-input range. Could be used to process any wide-varying signal that is to be read on a limited-range recording device such as a strip-chart recorder.

Hayden, J. L.↗
NASA NTRS1980

Incipient Failure Detection (IFD) of antifriction ball bearings

Two methods were investigated for retrieving the ball bearing signals buried by the overall signature of an operating large engine such as the main space shuttle engine. The signal averaging method averages n** signals over a time duration equaling the known period of the ball bearing defect frequency. With this method, the desired ball bearing defect signal will be enhanced over the noise by a factor of the square root of n. A second method is to perform a further frequency analysis on the logarithmic spectrum in order to detect and separate different families of harmonics and sidebands, thereby giving information about modulating frequencies. These two alternate IFD methods were carried out with a Norland 3001 waveform and data system. The obtained results are then compared with the power spectral density (PSD) of the overall machine signals and conclusions are made accordingly.

Wang, D. Y.↗
NASA NTRS1981

Determination of wind from NIMBUS 6 satellite sounding data

Objective methods of computing upper level and surface wind fields from NIMBUS 6 satellite sounding data are developed. These methods are evaluated by comparing satellite derived and rawinsonde wind fields on gridded constant pressure charts in four geographical regions. Satellite-derived and hourly observed surface wind fields are compared. Results indicate that the best satellite-derived wind on constant pressure charts is a geostrophic wind derived from highly smoothed fields of geopotential height. Satellite-derived winds computed in this manner and rawinsonde winds show similar circulation patterns except in areas of small height gradients. Magnitudes of the standard deviation of the differences between satellite derived and rawinsonde wind speeds range from approximately 3 to 12 m/sec on constant pressure charts and peak at the jet stream level. Fields of satellite-derived surface wind computed with the logarithmic wind law agree well with fields of observed surface wind in most regions. Magnitudes of the standard deviation of the differences in surface wind speed range from approximately 2 to 4 m/sec, and satellite derived surface winds are able to depict flow across a cold front and around a low pressure center.

Carle, W. E.↗
NASA NTRS1981

Surface geometry of circular cut spiral bevel gears

The tooth surface principal radii of curvature of crown (flat) gears were determined. Specific results are presented for involute, straight, and hyperbolic cutter profiles. It is shown that the geometry of circular cut spiral bevel gears is somewhat simpler than a theoretical logarithmic spiral bevel gear.

Huston, R. L.↗
NASA NTRS1981

Development and design of three monitoring instruments for spacecraft charging

A set of instruments which provide early detection of potentially dangerous geomagnetic substorm conditions and monitor the spacecraft response are discussed. The set consists of a sensor that measures the characteristic energy of collected electrons or ions from + 100 to - 20,000 V, a logarithmic current density sensor that measures local electron flux and a transient events counter that counts the spurious pulses from electrostatic discharges that couple into the spacecraft wiring harness. Design details and performance characteristics of the three instruments are given. Size, weight, and power requirements are minimized.

Sturman, J. C.↗
NASA NTRS1980

History of the mass of Mercury

This paper discusses the calculation of the masses of planets, as a means to construct reliable tables for their positions. Emphasis is placed on the four inner planets and the moon, with additional consideration given to the history of the masses of Jupiter and Saturn. A smooth curve can be drawn with the logarithm of the masses of the earth, Venus, Mars, and the moon, but the point for Mercury lies substantially off the curve. An investigation of the material content, surface examination, and planet radius for the planets leads to a reexamination of the history of the value for the mass of Mercury.

Lyttleton, R. A.↗
NASA NTRS1981

Turbulent boundary layer over solid and porous surfaces with small roughness

The turbulent boundary layer over a smooth, solid wall is examined along with a sandpaper-roughened, solid wall, and a porous wall. Suitable results are obtained with the smooth, solid wall for the Law of the Wall, the Defect Law, and the axial and turbulence intensities. The logarithmic portion of the Wall Law is shifted in the sandpaper-roughened, solid wall and an increase in the normal turbulence intensity and Reynolds stress is observed. An increase in the local skin friction values and all the turbulence values is found with the porous wall. The influence of a slightly rough, porous wall of sintered metal on the boundary layer is compared with a solid sandpaper-roughened wall in the same nominal K(+) range.

Kong, F. Y.↗
NASA NTRS1981

Organized motion in turbulent flow

A review of organized motion in turbulent flow indicates that the transport properties of most shear flows are dominated by large-scale vortex nonrandom motions. The mean velocity profile of a turbulent boundary layer consists of a viscous sublayer, buffer layer, and a logarithmic outer layer; an empirical formula of Coles (1956) applies to various pressure gradients. The boundary layer coherent structure was isolated by the correlation methods of Townsend (1956) and flow visualization by direct observations of complex unsteady turbulent motions. The near-wall studies of Willmart and Wooldridge (1962) used the space-time correlation for pressure fluctuations at the wall under a thick turbulent boundary layer; finally, organized motion in free shear flows and transition-control of mixing demonstrated that the Reynolds number invariance of turbulence shows wide scatter.

Cantwell, B. J.↗