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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 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

On convection-induced viscosity in accretion disks in cataclysmic variables

The vertical structure of accretion disks in cataclysmic variable systems is examined on the assumption that the convection is solely responsible for inducing the viscous heating. The viscous heating is distributed over the entire vertical structure so that purely radiative zones are able to carry a radial mass flux. The convective flux is computed by two different methods in separate calculations and the results from each method are compared. The values of the viscosity obtained are compared with those values inferred from the observed time scales of dwarf nova eruptions. Sequences of equilibrium solutions for constant radius and varying mass accretion rate are examined, the relations between viscosity and surface density are discussed in the context of recent models for the eruptions of dwarf novae.

Cannizzo, John K.↗
NASA NTRS1989

Ballistic transport in planetary ring systems due to particle erosion mechanisms. I - Theory, numerical methods, and illustrative examples

Ballistic transport, defined as the net radial transport of mass and angular momentum due to exchanges of meteoroid hypersonic-impact ejecta by neighboring planetary ring regions on time-scales orders-of-magnitude shorter than the age of the solar system, is presently considered as a problem in mathematical physics. The preliminary results of a numerical scheme for following the combined effects of ballistic transport and viscous diffusion demonstrate that ballistic transport generates structure near sharp edges already present in the ring-mass distribution; the entire ring system ultimately develops an undulatory structure whose length scale is typically of the order of the radial excursion of the impact ejecta.

Durisen, Richard H.↗
NASA NTRS1989

Automated generation of influence functions for planar crack problems

A numerical procedure for the generation of influence functions for Mode I planar problems is described. The resulting influence functions are in a form for convenient evaluation of stress-intensity factors for complex stress distributions. Crack surface displacements are obtained by a least-squares solution of the Williams eigenfunction expansion for displacements in a cracked body. Discrete values of the influence function, evaluated using the crack surface displacements, are curve fit using an assumed functional form. The assumed functional form includes appropriate limit-behavior terms for very deep and very shallow cracks. Continuous representation of the influence function provides a convenient means for evaluating stress-intensity factors for arbitrary stress distributions by numerical integration. The procedure is demonstrated for an edge-cracked strip and a radially cracked disk. Comparisons with available published results demonstrate the accuracy of the procedure.

Sire, Robert A.↗
NASA NTRS1990

Electric current in a unipolar sunspot with an untwisted field

The return flux (RF) sunspot model is applied to a round, unipolar sunspot observed by H. Kawakami (1983). Solving the magnetohydrostatic problem using the gas pressure deficit between the umbral and quiet-sun atmospheres as a source function, a distribution of electric current density in an untwisted, unipolar sunspot as a function of height and radial distance from the sunspot center is observed. Maximum electric current density is about 32 mA/sq m at the bottom of the sunspot.

Osherovich, V. A.↗
NASA NTRS1991

Gas and drop behavior in reacting and non-reacting air-blast atomizer sprays

A detailed study of the two-phase flow produced by a gas-turbine air-blast atomizer is performed with the goal of identifying the interaction between the two phases for both nonreacting and reacting conditions. A two-component phase Doppler interferometry is utilized to characterize three flowfields produced by the atomizer: (1) the single-phase flow, (2) the two-phase nonreacting spray, and (3) the two-phase reacting spray. Measurements of the mean and fluctuating axial and azimuthal velocities for each phase are obtained. In addition, the droplet size distribution, volume flux, and concentration are measured. The results reveal the strong influence of the dispersed phase on the gas, and the influence of reaction on both the gas and the droplet field. The presence of the spray significantly alters the inlet condition of the atomizer. With this alteration quantified, it is possible to deduce that the inertia associated with the dispersed phase damps the fluctuating velocities of the gas. Reaction reduces the volume flux of the droplets, broadens the local volume distribution of the droplets in the region of the reaction zone, increases the axial velocities and radial spread of the gas, and increases the anisotropy in the region of the reaction zone.

Mcdonell, Vincent G.↗
NASA NTRS1992

Two-population model for the sources of gamma-ray bursts

It is shown here that no single class of gamma-ray bursts, either Galactic or cosmological in origin can explain recent observations which suggest that the distribution of gamma-ray burst sources is isotropic about the earth's position but also radially nonuniform. It is argued that the constraints can be reconciled if there are at least two distinct classes of bursts. Two kinds of burst are considered which both originate on Galactic neutron stars but which differ in intrinsic luminosity by a factor of 10 exp 5.

Lingenfelter, R. E.↗
NASA NTRS1997

Enhancement of Nucleate Boiling Heat Flux on Macro/Micro-Structured Surfaces Cooled by Multiple Impinging Jets

An experimental investigation of nucleate boiling heat transfer from modified surfaces cooled by multiple in-line impinging circular jets is reported and found to agree with single jet results. A copper block is heated from the back by two electrical arcs, and cooled on the opposite side by three identical liquid jets of distilled water at subcoolings of 25 C 50 C and 77 C and Freon 113 at 24 C subcooling. Liquid flow rates are held constant at 5, 10, and 15 GPH for each of the three jets with jet velocities ranging from 1.4 m/s to 1 1.2 m/s and jet diameters from 0.95 mm to 2.2 mm. To increase the maximum heat flux (CHF) and heat removal rate, the boiling surface was modified by both macro and micro enhancements. Macro modification consists of machined radial grooves in the boiling surface arranged in an optimally designed pattern to allow better liquid distribution along the surface. These grooves also reduce splashing of liquid droplets, and provide 'channels' to sweep away bubbles. Micro modification was achieved by flame spraying metal powder on the boiling surface, creating a porous, sintered surface. With the addition of both micro and macro structured enhancements, maximum heat flux and nucleate boiling can be enhanced by more than 200%. Examination of each surface modification separately and together indicates that at lower superheats, the micro structure provides the enhanced heat transfer by providing more nucleation sites, while for higher superheats the macro structure allows better liquid distribution and bubble removal. A correlation is presented to account for liquid subcoolings and surface enhancements, in addition to the geometrical and fluid properties previously reported in the literature.

Kugler, Scott Lee↗
NASA NTRS1999

High Pressure Water Stripping Using Multi-Orifice Nozzles

The use of multi-orifice rotary nozzles greatly increases the speed and stripping effectiveness of high pressure water blasting systems, but also greatly increases the complexity of selecting and optimizing the operating parameters. The rotational speed of the nozzle must be coupled with its transverse velocity as it passes across the surface of the substrate being stripped. The radial and angular positions of each orifice must be included in the analysis of the nozzle configuration. Orifices at the outer edge of the nozzle head move at a faster rate than the orifices located near the center. The energy transmitted to the surface from the impact force of the water stream from an outer orifice is therefore spread over a larger area than energy from an inner orifice. Utilizing a larger diameter orifice in the outer radial positions increases the total energy transmitted from the outer orifice to compensate for the wider distribution of energy. The total flow rate from the combination of all orifices must be monitored and should be kept below the pump capacity while choosing orifice to insert in each position. The energy distribution from the orifice pattern is further complicated since the rotary path of all the orifices in the nozzle head pass through the center section. All orifices contribute to the stripping in the center of the path while only the outer most orifice contributes to the stripping at the edge of the nozzle. Additional orifices contribute to the stripping from the outer edge toward the center section. With all these parameters to configure and each parameter change affecting the others, a computer model was developed to track and coordinate these parameters. The computer simulation graphically indicates the cumulative affect from each parameter selected. The result from the proper choices in parameters is a well designed, highly efficient stripping system. A poorly chosen set of parameters will cause the nozzle to strip aggressively in some areas while leaving the coating untouched in adjacent sections. The high pressure water stripping system can be set to extremely aggressive conditions allowing stripping of hard to remove adhesives, paint systems, and even cladding and chromate conversion coatings. The energy force can also be reduced to strip coatings from thin aluminum substrates without causing any damage or deterioration to the substrate's surface. High pressure water stripping of aerospace components has thus proven to be an efficient and cost effective method for cleaning and removing coatings.

Hoppe, David↗
NASA NTRS2001

Airborne Differential Doppler Weather Radar

The Precipitation Radar aboard the Tropical Rain Measuring Mission (TRMM) Satellite has shown the potential for spaceborne sensing of snow and rain by means of an incoherent pulsed radar operating at 13.8 GHz. The primary advantage of radar relative to passive instruments arises from the fact that the radar can image the 3-dimensional structure of storms. As a consequence, the radar data can be used to determine the vertical rain structure, rain type (convective/stratiform) effective storm height, and location of the melting layer. The radar, moreover, can be used to detect snow and improve the estimation of rain rate over land. To move toward spaceborne weather radars that can be deployed routinely as part of an instrument set consisting of passive and active sensors will require the development of less expensive, lighter-weight radars that consume less power. At the same time, the addition of a second frequency and an upgrade to Doppler capability are features that are needed to retrieve information on the characteristics of the drop size distribution, vertical air motion and storm dynamics. One approach to the problem is to use a single broad-band transmitter-receiver and antenna where two narrow-band frequencies are spaced apart by 5% to 10% of the center frequency. Use of Ka-band frequencies (26.5 GHz - 40 GHz) affords two advantages: adequate spatial resolution can be attained with a relatively small antenna and the differential reflectivity and mean Doppler signals are directly related to the median mass diameter of the snow and raindrop size distributions. The differential mean Doppler signal has the additional property that this quantity depends only on that part of the radial speed of the hydrometeors that is drop-size dependent. In principle, the mean and differential mean Doppler from a near-nadir viewing radar can be used to retrieve vertical air motion as well as the total mean radial velocity. In the paper, we present theoretical calculations for the differential reflectivity and Doppler as functions of the center frequency, frequency difference, and median mass diameter. For a fixed pair of frequencies, the detectability of the differential signals can be expressed as the number of independent samples required to detect rain or snow with a particular median mass diameter. Because sampling numbers on the order of 1000 are needed to detect the differential signal over a range of size distributions, the instrument must be confined to a near-nadir, narrow swath. Radar measurements from a zenith directed radar operated at 9.1 GHz and 10 GHz are used to investigate the qualitative characteristics of the differential signals. Disdrometer and rain gauge data taken at the surface, just below the radar, are used to test whether the differential signals can be used to estimate characteristics of the raindrop size distribution.

Meneghini, R.↗
NASA NTRS2018

Aerodynamic Design and Optimization of Fan Stage for Boundary Layer Ingestion Propulsion System

The present paper addresses the process of preliminary design of a low-pressure fan and outlet guide vane (OGV) of a boundary layer ingestion (BLI) propulsion system. The tail-cone thruster systems of NASA's STARC_ABL (Single-aisle Turboelectric Aircraft with an Aft Boundary-Layer propulsor) adopts an axi-symmetric BLI type inlet as opposed to other embedded engine systems. Thus, the focus of the present work is placed on maximizing the efficiency of the fan and OGV stages under a significant radial distortion. A parameterization with B-spline function for camber line angles, metal chord, thickness distribution and stacking axis of blades is presented. The flowpath lines are also parameterized by B-spline function and aggregated in the design system of blades. The design optimization with evolutionary algorithm is performed with constraints of fan pressure ratio, OGV exit swirl angle and nozzle exit properties. The inlet conditions for the turbo-machinery CFD (Computational Fluid Dynamics) domain and the design goal of the fan stage are driven by a propulsion airframe integration (PAI) model that uses a 3-D unstructured RANS (Reynolds Average Navier Stokes) solver and actuator disk model. The expected power saving of the BLI propulsor is quantified via PAI analysis and the resulting preliminary design of the fan stages is compared with a clean-inlet flow propulsor.

Turbo-machinery↗
NASA NTRS2016

Frequency-Range Distribution of Boulders Around Cone Crater: Relevance to Landing Site Hazard Avoidance

Boulders represent a landing hazard that must be addressed in the planning of future landings on the Moon. A boulder under a landing leg can contribute to deck tilt and boulders can damage spacecraft during landing. Using orbital data to characterize boulder populations at locations where landers have safely touched down (Apollo, Luna, Surveyor, and Chang'e-3 sites) is important for determining landing hazard criteria for future missions. Additionally, assessing the distribution of boulders can address broader science issues, e.g., how far craters distribute boulders and how this distribution varies as a function of crater size and age. The availability of new Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) images [1] enables the use of boulder size- and range frequency distributions for a variety of purposes [2-6]. Boulders degrade over time and primarily occur around young or fresh craters that are large enough to excavate bedrock. Here we use NAC images to analyze boulder distributions around Cone crater (340 m diameter) at the Apollo 14 site. Cone crater (CC) was selected because it is the largest crater where astronaut surface photography is available for a radial traverse to the rim. Cone crater is young (approximately 29 Ma [7]) relative to the time required to break down boulders [3,8], giving us a data point for boulder range-frequency distributions (BRFDs) as a function of crater age.

Clegg-Watkins, R. N.↗
NASA NTRS1983

On the equation of state of solar wind ions derived from Helios measurements

The radial evolution of such adiabatic invariants as the ion magnetic moments are studied on the basis of solar wind ion velocity distribution observations made by the Helios spacecraft between 0.3 and 1 AU. Significant differences between proton and alpha-particle parameters in wind velocity dependence are noted, and adiabaticity is on the average found to be violated. This violation is interpreted as evidence that protons are heated perpendicular to the field in fast streams. The contribution of the differential streaming energy to the total internal energy of the ions is also considered, and average heliocentric radial profiles for the ion heat fluxes are presented together with an examination of a possible ion heat flux role in the supply of thermal energy during the winds radial expansion. The present findings suggest that wave-particle interactions, and/or Coulomb collisions, are required to explain solar wind ion thermal energy states and radial temperature profiles.

Marsch, E.↗
NASA NTRS1983

The mass dependence of wave particle interactions as observed with the ISEE-1 energetic ion mass spectrometer

Simultaneous measurements of the O(+) and H(+) distributions from two transverse acceleration events in the high altitude auroral ionosphere are presented. The data were acquired from the energetic ion mass spectrometer on the ISEE-1 satellite, in the dusk sector, on auroral field lines (L = 8-9), at geocentric radial distances of about 3 earth radii. Temporal and/or spatial fluctuations during the measurement cycle resulted in some scatter of the data points, but the transverse velocity distributions are reasonably well represented by maxwellians at energies in the few hundred eV range. The transverse temperatures were about 60 eV in both cases and no significant differences were observed between the temperatures of the O(+) and H(+). The flux intensities of the two ion species were also generally comparable.

Sharp, R. D.↗
NASA NTRS1995

The influence of intermediate-scale variations in the heliospheric magnetic field on the transport of galactic cosmic rays

Variations in the heliospheric magnetic field occur on most scales including those lying intermediate between the gyro-radii of galactic cosmic rays and heliocentric radial distance. It is demonstrated that a correlation exists between these intermediate-scale variations in the magnetic field and the variations in the cosmic ray distribution function that result from the field variations. This correlation will affect the average transport of galactic cosmic rays by significantly altering the patterns of gradient and curvature drifts in the heliosphere. During the current solar cycle, the altered drift patterns can lead to larger radial gradients of the galactic cosmic rays and significantly smaller latitude gradients than is expected only from drifts in the mean magnetic field.

Fisk, L. A.↗
NASA NTRS1991

Plasma transport in the Io torus - The importance of microscopic diffusion

This paper considers the question of whether the distribution of mass in the Io plasma torus is consistent with the concept of interchange eddy transport. Specifically, the flux tube content exhibits a gradual decrease with increasing radial distance from the source near Io without any evidence for substantial density irregularity associated with the plasma source or loss. Using a simple one-dimensional numerical model to simulate macroscopic interchange eddy transport, it is demonstrated that this smooth equilibrium distribution of mass can occur but only with the inclusion of a minimal level of small scale microscopic mixing at a rate approaching Bohm diffusion. Otherwise, the system exhibits a chaotic appearance which never approaches an equilibrium distribution. Various physical mechanisms for the microscopic diffusion process which is required to provide a sufficiently rapid mixing of material between the macroscopic eddies are discussed.

Mei, YI↗
NASA NTRS1994

Observations of nonadiabatic acceleration of ions in Earth's magnetotail

We present observations of the three-dimensional velocity distributions of protons in the energy range 20 eV to 52 keV at locations within and near the current sheet of Earth's magnetotail at geocentric radial distances 35 to 87 R(sub E). These measurements were acquired on December 8, 1990, with a set of electrostatic analyzers on board the Galileo spacecraft during its approach to Earth in order to obtain one of its gravitational assists to Jupiter. It is found that the velocity distributions are inadequately described as quasi-Maxwellian distributions such as those found in the central plasma sheet at positions nearer to Earth. Instead the proton velocity distributions can be categorized into two major types. The first type is the 'lima bean' shaped distribution with high-speed bulk flows and high temperatures that are similar to those found nearer to Earth in the plasma sheet boundary layer. The second type consists of colder protons with considerably lesser bulk flow speeds. Examples of velocity distributions are given for the plasma mantle, a region near the magnetic neutral line, positions earthward and tailward of the neutral line, and the plasma sheet boundary layer. At positions near the neutral line, only complex velocity distributions consisting of the colder protons are found, whereas both of the above types of distributions are found in and near the current sheet at earthward and tailward locations. Bulk flows are directed generally earthward and tailward at positions earthward and tailward of the neutral line, respectively. Only the high-speed, hot distribution is present in the plasma sheet boundary layer. The observations are interpreted in terms of the nonadiabatic acceleration of protons that flow into the current sheet from the plasma mantle. For this interpretation the hot, 'lima bean' shaped distributions are associated with meandering, or Speiser, orbits in the current sheet. It is suggested that the colder, lower-speed proton velocity distributions are the result of fractional or few gyromotions before ejection out of the current sheet, but this speculation must be further investigated with appropriate kinetic simulation of trajectories.

Frank, L. A.↗
NASA NTRS1987

The influence of strong hydromagnetic turbulence on newborn cometary ions

By means of a test particle model, the time evolution of the velocity distribution function of newborn cometary ions in the presence of strong hydromagnetic turbulence is studied. The test particle model employs a realistic spectrum of hydromagnetic turbulence corresponding to the observations of the International Cometary Explorer spacecraft at Comet Giacobini-Zinner. It is found that pitch-angle scattering processes can rapidly result in the formation of the shell distribution which has been observed near Comets Giacobini-Zinner and Halley. The model also indicates that radial diffusion in velocity space develops on a much longer time scale.

Price, C. P.↗
NASA NTRS1992

Analysis of Antarctic stratospheric aerosol properties using SAGE II extinction measurements

Multispectra aerosol extinction data for the fall and spring of 1987 measured by the SAGE II sensor are employed to determine the physical characteristics of aerosols within the springtime Antarctic polar vortex. Attention is given to the physical processes that give rise to the apparent springtime 'cleansing' of the Antarctic stratosphere. The inferred vertical and radial structure compare favorably with in situ measurements but yield a previously unavailable 2D structure to the distribution of aerosols within the polar vortex. The springtime 'cleansing' of the Antarctic stratosphere is found to be a result of both large-scale subsidence and the preferential removal of large particles by the nucleation and subsequent sedimentation of polar stratospheric clouds.

Thomason, Larry W.↗