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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

The derivation of temperature gradient and electron density maps from EUV spectroheliograms.

We discuss spatial variations in electron density at the base of the corona and in the temperature gradient in the chromospheric-coronal transition layer as determined from analysis of maps constructed from Mg X and O VI spectroheliograms. Both the mapping techniques and results of analyzing EUV spectra from OSO 6 observations are presented. Comparisons of these maps with photospheric magnetograms and spectroheliograms made in chromospheric EUV lines and continua indicate that the electron density and temperature gradient in the transition layer tend to be enhanced in areas where the photospheric magnetic field and chromospheric EUV emission are enhanced. Relationships among the coronal electron density, transition-layer temperature gradient, chromospheric emission, and photospheric magnetic field strength are derived.

Withbroe, G. L.↗
NASA NTRS1972

The turbulent boundary layer on a porous plate: An experimental study of the heat transfer behavior with adverse pressure gradients

An experimental investigation of the heat transfer behavior of the near equilibrium transpired turbulent boundary layer with adverse pressure gradient has been carried out. Stanton numbers were measured by an energy balance on electrically heated plates that form the bottom wall of the wind tunnel. Two adverse pressure gradients were studied. Two types of transpiration boundary conditions were investigated. The concept of an equilibrium thermal boundary layer was introduced. It was found that Stanton number as a function of enthalpy thickness Reynolds number is essentially unaffected by adverse pressure gradient with no transpiration. Shear stress, heat flux, and turbulent Prandtl number profiles were computed from mean temperature and velocity profiles. It was concluded that the turbulent Prandtl number is greater than unity in near the wall and decreases continuously to approximately 0.5 at the free stream.

Blackwell, B. F.↗
NASA NTRS1973

A piloted simulation study of the effects of controller force gradient in VTOL hovering flight

A study of the effect of control force gradient on the VTOL visual hovering task was conducted on the NASA-Ames Research Center Six-Degree-of-Freedom Motion Simulator. Lateral control force-gradient characteristics were evaluated in combination with three different types of stabilization systems: An unstabilized (acceleration) system, a rate-stabilized system, and two attitude-stabilized systems. The effects of gust disturbances were included in the control force evaluation for the attitude systems. A force gradient of 1.0 lb/in was within the optimum range for all control systems and conditions evaluated in this study.

Fry, E. B.↗
NASA NTRS1973

The behavior of a compressible turbulent boundary layer in a shock-wave-induced adverse pressure gradient

The results of an experimental investigation of the mean- and fluctuating-flow properties of a compressible turbulent boundary layer in a shock-wave-induced adverse pressure gradient are presented. The turbulent boundary layer developed on the wall of an axially symmetric nozzle and test section whose nominal free-stream Mach number and boundary-layer thickness Reynolds number were 4 and 100,000, respectively. The adverse pressure gradient was induced by an externally generated conical shock wave. Mean and time-averaged fluctuating-flow data, including the complete experimental Reynolds stress tensor and experimental turbulent mass- and heat-transfer rates are presented for the boundary layer and external flow, upstream, within and downstream of the pressure gradient. The mean-flow data include distributions of total temperature throughout the region of interest. The turbulent mixing properties of the flow were determined experimentally with a hot-wire anemometer. The calibration of the wires and the interpretation of the data are discussed. From the results of the investigation, it is concluded that the shock-wave - boundary-layer interaction significantly alters the turbulent mixing characteristics of the boundary layer.

Rose, W. C.↗
NASA NTRS1973

Stochastic estimates of gradient from laser measurements for an autonomous Martian roving vehicle

The general problem of estimating the state vector x from the state equation h = Ax where h, A, and x are all stochastic, is presented. Specifically, the problem is for an autonomous Martian roving vehicle to utilize laser measurements in estimating the gradient of the terrain. Error exists due to two factors - surface roughness and instrumental measurements. The errors in slope depend on the standard deviations of these noise factors. Numerically, the error in gradient is expressed as a function of instrumental inaccuracies. Certain guidelines for the accuracy of permissable gradient must be set. It is found that present technology can meet these guidelines.

Burger, P. A.↗
NASA NTRS1974

Mean and fluctuating flow measurements in axisymmetric supersonic boundary layer flow subjected to distributed adverse pressure gradients

Measurements have been made of the mean flow properties and turbulent fluctuations in adiabatic turbulent boundary layer flows subjected to distributed adverse pressure gradients. In the freestream region upstream of the adverse pressure gradient the Mach number was 3.86, the unit Reynolds number 5.3 million per foot. The boundary layer developed on the wall of an axisymmetric nozzle and straight test section. In order to avoid the effects of streamwise surface curvature the adverse pressure gradients at the test section wall were induced by contoured centerbodies mounted on the wind tunnel centerline. The flow under study simulated that which might be found in an axially symmetric engine inlet of a supersonic aircraft.

Gootzait, E.↗
NASA NTRS1973

Stochastic estimates of gradient from laser measurements for an autonomous Martian Roving Vehicle

The general problem presented in this paper is one of estimating the state vector x from the state equation h = Ax, where h, A, and x are all stochastic. Specifically, the problem is for an autonomous Martian Roving Vehicle to utilize laser measurements in estimating the gradient of the terrain. Error exists due to two factors - surface roughness and instrumental measurements. The errors in slope depend on the standard deviations of these noise factors. Numerically, the error in gradient is expressed as a function of instrumental inaccuracies. Certain guidelines for the accuracy of permissable gradient must be set. It is found that present technology can meet these guidelines.-

Shen, C. N.↗
NASA NTRS1974

Effect of transverse velocity and temperature gradients on sound attenuation in two-dimensional ducts

An investigation is described of the effect of transverse mean-velocity and temperature gradients on sound attenuation in acoustically treated two-dimensional ducts. The results show that cooling the duct walls leads to channeling the sound toward the walls for both downstream and upstream propagation. The effect of mean-temperature gradients on the attenuation rates of the lowest three modes can be as important as the effect of mean-velocity gradients.

Nayfeh, A. H.↗
NASA NTRS1975

An experimental investigation of heat transfer to reusable surface insulation tile array gaps in a turbulent boundary layer with pressure gradient

An experimental investigation was performed to determine the effect of pressure gradient on the heat transfer to space shuttle reusable surface insulation (RSI) tile array gaps under thick, turbulent boundary layer conditions. Heat transfer and pressure measurements were obtained on a curved array of full-scale simulated RSI tiles in a tunnel wall boundary layer at a nominal freestream Mach number of 10.3 and freestream unit Reynolds numbers of 1.6, 3.3, and and 6.1 million per meter. Transverse pressure gradients were induced over the model surface by rotating the curved array with respect to the flow. Definition of the tunnel wall boundary layer flow was obtained by measurement of boundary layer pitot pressure profiles, and flat plate wall pressure and heat transfer. Flat plate wall heat transfer data were correlated and a method was derived for prediction of smooth, curved array heat transfer in the highly three-dimensional tunnel wall boundary layer flow and simulation of full-scale space shuttle vehicle pressure gradient levels was assessed.

Throckmorton, D. A.↗
NASA NTRS1974

Determination of the radial gradient in the region 0.81-1.0 AU using both high- and low-energy /more than 10-GeV and more than 52-MeV/ detectors for the 1-AU monitor

A determination of the radial gradient for alpha particles (31-46 MeV/nuc) and protons with energies above 7.5 MeV and 44-77 MeV in the region 1.0-0.81 AU is presented for the solar-quiet year 1966. The determinations are based on data from the Pioneer 6 space probe. Two different detectors are used: the Deep River neutron monitor and measurements of low energy protons made on the IMP-C satellite. The average energy response of the Deep River monitor is 16 GeV, whereas the IMP-C data is for protons with energies above 50 MeV. The resulting radial gradient is found to be nearly zero for the alpha particles and slightly negative for the protons. The same qualitative results were found using the IMP-C data and the Deep River neutron monitor to measure the temporal variation in the cosmic ray intensity. The present analysis indicates that detectors over a wide range of energies are suitable for measuring the radial gradient, providing sufficient statistical precision is obtained to evaluate short-term modulation and the azimuthal separation of the detectors is not great.

Sheldon, W. R.↗
NASA NTRS1976

Turbulence measurements in axisymmetric supersonic boundary layer flow in adverse pressure gradients

Measurements have been made of the mean-flow and turbulence properties in adiabatic turbulent boundary layer flows subjected to adverse pressure gradients. In the freestream region upstream of the adverse pressure gradient the Mach number was 3.86, the unit Reynolds number 5.3 million per foot. The boundary layer developed on the wall of an axisymmetric nozzle and straight test section. The pressure gradients at the test section wall were induced by contoured centerbodies mounted on the wind tunnel centerline. The flow under study simulated that which might be found in an axially symmetric engine inlet of a supersonic aircraft. The results obtained have shown good agreement to exist between the measured normalized turbulent velocity fluctuations and the results from other recent investigations of compressible boundary layers.

Gootzait, E.↗
NASA NTRS1975

The temperature gradient between 100 and 120 km

Oxygen density profiles inferred from Ogo 6 green nightglow emission vary too sharply between 100 and 120 km to be consistent with temperature gradients in standard model atmospheres, and the eddy diffusion coefficient K determined from these observations reaches its maximum below 115 km. For three atomic oxygen profiles obtained at geographic latitudes of -27.69, +48.89, and +59.10 the temperature profiles required to create a downward flux that varies with altitude as the integrated photolytic production rate above that altitude are calculated, assuming K to be invariant with altitude and latitude. The oxygen distribution can be reconciled with a constant eddy coefficient above 100 km if the temperature gradient reaches a value between 10 and 20 deg K/km for low values of the eddy coefficient (about 500,000 sq cm/sec) or between 30 and 50 deg K/km for a higher eddy coefficient (about 1.6 million sq cm/sec). The maximum gradient for the Jacchia (1971) model is about 10 deg K/km. These temperature profiles predict Ar/N ratios consistent with those measured by sounding rockets. The low K profiles are large enough to remove a large part of the solar energy deposited below 120 km by thermal conduction.

Donahue, T. M.↗
NASA NTRS1976

Effect of velocity gradients on measurements of turbulent shear stress

Experiments were carried out to evaluate the effects of normal velocity gradients on hot wire measurements in a subsonic boundary layer of the same size as the flow investigated by Johnson and Rose (1975). Both hot wire and film anemometers were used to measure the turbulent properties of the boundary layer. A special X-wire probe with one wire vertical and the other at an angle of about 40 deg to the flow was used to demonstrate the gradient effects. The results indicate that major errors are encountered when mean and turbulent velocity gradients exist along the length of hot wire sensors, the problem being more pronounced at high speeds. Although the split film sensor results show a significant improvement over the X-wire sensor, further reduction in the space resolution of sensors by roughly an order of magnitude would appear to be necessary to reduce the error to acceptable values near the wall.

Sandborn, V. A.↗
NASA NTRS1976

Evidence of a large-scale gradient in the solar wind velocity

Measurements of the solar wind velocity are compared at two widely separated locations, using plasma data obtained by Mariner 5, en route to Venus, and with the near-earth satellites Explorer 33, 34, and 35. A previous study of the propagation of interplanetary sector boundaries between Mariner and the earth had implied the existence of large scale velocity gradient which was interpreted as a latitude gradient of approximately 13 km/sec per degree of latitude. The results of the present investigation in which the earlier results were extended to the overall solar wind, without regard to the presence of sector boundaries, suggests that a latitude dependence of the solar wind velocity is the most plausible interpretation of the large-scale velocity gradient.

Rhodes, E. J., Jr.↗
NASA NTRS1976

A turbulence model for nonequilibrium adverse pressure gradient flows

This paper presents a method for calculating compressible adverse pressure gradient boundary layers by using an algebraic eddy viscosity turbulence model that has been modified for variable pressure gradient and turbulence memory effects. The pressure gradient corrections are based on previous incompressible data correlations. Several methods for including the effects of turbulence memory are evaluated. A new lag model, which gives good agreement with available experimental data, is developed. Finally, a correlation is developed for the lag length parameter employed in the model as a function of the known experimental flow variables.

Horstman, C. C.↗
NASA NTRS1976

Effects of a magnetic field gradient on the lower hybrid drift instability

The effect of a magnetic field gradient on the lower hybrid drift instability is examined in the low drift velocity regime (i.e., of the order of the ion thermal velocity). The theoretical model includes density and temperature gradients, and considers only waves propagating perpendicular to the ambient magnetic field with wavelengths of the order of the electron Larmor radius. It is found, for the case of a finite ratio of the electron pressure to the magnetic field pressure, that a magnetic gradient drift-wave resonance can be important and is stabilizing or destabilizing depending upon the physical conditions. Substantial plasma heating and a large anomalous resistivity can also occur.

Huba, J. D.↗
NASA NTRS1977

Influence of two-dimensional hygrothermal gradients on interlaminar stresses near free edges

Interlaminar stresses are determined for mechanical loading, uniform hygrothermal loading, and gradient moisture loading through implementation of a finite element computer code. Nonuniform two-dimensional hygroscopic gradients are obtained from a finite difference solution of the diffusion equation. It is shown that hygroscopic induced stresses can be larger than those resulting from mechanical and thermal loading, and that the distribution of the interlaminar normal stress may be changed significantly in the presence of a two-dimensional moisture gradient in the boundary layer of a composite laminate.

Farley, G. L.↗
NASA NTRS1976

Cosmic-ray gradients from Pioneer-10 and Pioneer-11

The paper reports Pioneer 10 and 11 observations of the variation with heliocentric distance of the intensity of cosmic-ray protons, alpha particles, and high-Z nuclei with kinetic energies of at least 480 MeV/nucleon as well as cosmic-ray electrons with energies exceeding 6 MeV. The observations were with three-channel Cerenkov counters at distances between 1.02 and 4.66 AU while the spacecraft traveled from earth to Jupiter. During the 4.5-month observation period, all the counting rates rose steadily, except when they were modified by solar events, Forbush decreases, and Jovian electron events. Two methods are employed to determine the cosmic-ray integral intensity gradient for the observation period from simultaneous data obtained by the two spacecraft; effects of solar particles, Forbush decreases, and Jovian electrons are eliminated in various ways. A radial gradient of 0.15 + or - 2.3% per AU is determined, which is considered to be consistent with zero. Theoretical gradients are computed, and the observed values are found to be an order of magnitude below the expected values. Several reasons for the discrepancy are suggested.

Axford, W. I.↗