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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Spacelab experiment definition study on phase transition and critical phenomena in fluids: Interim report on experimental justification

Pure fluids and fluid mixtures near critical points are identified and are related to the progress of several disciplines. Consideration is given to thermodynamic properties, transport properties, and the complex nonlinear phenomena which occur when fluids undergo phase transitions in the critical region. The distinction is made between practical limits which may be extended by advances in technology and intrinsic ones which arise from the modification of fluid properties by the earth's gravitational field. The kinds of experiments near critical points which could best exploit the low gravity environment of an orbiting laboratory are identified. These include studies of the index of refraction, constant volume specific heat, and phase separation.

Moldover, M. R.↗
NASA NTRS1976

Convection phenomena at reduced gravity of importance for materials processing

The basic aspects of convection processes are delineated. It is shown that even in weak gravitational fields buoyancy can induce fluid motions. Furthermore, at reduced gravity other nongravity forces such as surface or interfacial tensions, g-jitter, therma-volume expansions, density differences due to phase changes, and magnetic and electric fields can induce fluid motions. The various types of flow possible with these various driving forces are described and criteria for determining the extent and nature of the resulting flows and heat transfer are presented. The various physical mechanisms that can occur separately and in combination are indicated and the present state of knowledge of each of the phenomena is outlined.

Ostrach, S.↗
NASA NTRS1976

Simulated traveling interplanetary disturbances initiated by various solar phenomena

Earlier studies have shown that interplanetary disturbances observed by spacecraft at large heliocentric distances from the sun can be directly associated with various solar activities such as surges, sprays, eruptive prominences, and flares. A digital computer code to simulate these phenomena is developed. This numerical code solves a set of conservation equations for an adiabatic time-dependent spherically-symmetric fluid flow. The solar events are simulated by perturbations in the dependent variables at the lower boundary of the quiet sun corona, and the time-dependent numerical solution simulates the coronal response. Three physical cases are simulated by using the proposed numerical code: (1) part of a surge, spray and prominence; (2) a single flare; and (3) two flares whose interplanetary consequences interact in space. Results for the first two cases are compared with both ground-based and space probe observations. Fairly good agreement with observations is found. A comparison of the third case with observations is presently under way.

Dryer, M.↗
NASA NTRS1976

Effects of propagation phenomena and frequency allocation on the growth of satellite communications

The development of new allocations and new frequency and orbit sharing criteria for satellite communications below 10 GHz is discussed. These criteria are dependent on the outcome of current spectrum and orbit utilization and propagation studies addressing such problems as intersystem interference, satellite spacing, positioning, and repositioning, spillover of radio signals across geographic boundaries, and the adverse effects of propagation phenomena. These problems are discussed in relation to preparations for the 1979 General World Administrative Radio Conference.

Freibaum, J.↗
NASA NTRS1977

Convection phenomena of importance for materials processing in space

The basic aspects of convection processes are delineated. It is shown that even in weak gravitational fields buoyancy can induce fluid motion. Furthermore, at reduced gravity, other nongravity forces such as surface or interfacial tensions, g jitter, thermal volume expansions, density differences due to phase changes, and magnetic and electric fields can induce fluid motions. The types of flows possible with these various driving forces are described, and criteria for determining the extent and nature of the resulting flows and heat transfer are presented. The different physical mechanisms that can occur separately and in combination are indicated, and the present state of knowledge of each of the phenomena is outlined. Specific research problems are described for many of the types of convection that are necessary to obtain greater understanding of their implications for space processing.

Ostrach, S.↗
NASA NTRS1978

Some flow phenomena in a constant area duct with a Borda type inlet including the critical region

Mass limiting flow characteristics for a 55 L/D tube with a Borda type inlet were assessed over large ranges of temperature and pressure, using fluid nitrogen. Under certain conditions, separation and pressure drop at the inlet was sufficiently strong to permit partial vaporization and the remaining fluid flowed through the tube as if it were a free jet. An empirical relation was determined which defines conditions under which this type of flow can occur. A flow coefficient is presented which enables estimations of flow rates over the experimental range. A flow rate stagnation pressure map for selected stagnation isotherms and pressure profiles document these flow phenomena.

Hendricks, R. C.↗
NASA NTRS1977

Martian Dynamical Phenomena During June-November 1976: Viking Orbiter Imaging Results

A summary is presented of the orbital imaging observations of dynamical phenomena on Mars during the Viking primary mission. Clouds in the Tharsis/Amazonis regions are examined and the observation of an area of unusually high brightness to the southwest of Arsia Mons is considered. Attention is given to clouds and surface frost in the south polar region, the north polar cap, and aspects of dust storm activity.

Briggs, G.↗
NASA NTRS1977

Optical design of a stigmatic spectroheliometer for photometric studies of dynamic phenomena at extreme-ultraviolet wavelengths

The design of a stigmatic spectroheliometer for photometric studies of dynamic phenomena in the solar atmosphere at extreme ultraviolet (EUV) wavelengths is described. The normal-incidence spectrometer requires only one reflective surface, and is equipped with a series of exit slits and associated one-dimensional detector arrays that are mounted at the secondary (vertical) foci of the concave diffraction grating. It is shown that such a spectrometer mounted at the focus of an off-axis paraboloid telescope mirror of the size employed in the EUV spectroheliometer flown on Skylab could record monochromatic images of a 2 x 2 (arcmin) sq field-of-view with a spatial resolution element of 1 x 1 (arcsec) sq in a time of 4 s, 24 s, or 4 min, depending on whether the region studied is flaring, active, or quiet. The resulting spectroheliograms would have an average photometric precision of 10% and a spectral purity of 0.1 A.

Huber, M. C. E.↗
NASA NTRS1978

Visual phenomena induced by relativistic carbon ions with and without Cerenkov radiation

Exposing the human eye to individual carbon ions moving at relativistic speeds results in visual phenomena that include point flashes, streaks, and larger diffuse flashes. The diffuse flashes have previously been observed by astronauts in space but not in laboratory experiments with particles of high atomic number and energy. They are observed only when the nucleus moves fast enough to generate Cerenkov radiation.

Mcnulty, P. J.↗
NASA NTRS1976

Large Area Crop Inventory Experiment (LACIE). Detection of episodic phenomena on LANDSAT imagery

The author has identified the following significant results. Episodic phenomena such as rainfall shortly before data pass, thin translucent clouds, cloud shadows, and aircraft condensation trails and their shadows are responsible for changes in the spectral reflectivities of some surfaces. These changes are readily detected on LANDSAT full-frame imagery. Histograms of selected areas in Kansas show a distinct decrease in mean radiance values, but also, an increase in scene contrast, in areas where recent rains had occurred. Histograms from a few individual fields indicate that the mean radiance values for winter wheat followed a different trend after a rainfall than alfalfa or grasses.

Chesnutwood, C. M.↗
NASA NTRS1978

Significance of radiation models in investigating the flow phenomena around a Jovian entry body

Formulation is presented to demonstrate the significance of a simplified radiation model in investigating the flow phenomena in the viscous radiating shock layer of a Jovian entry body. The body configurations used are a 55 degree sphere cone and 50 degree hyperboloid. A nongray absorption model for hydrogen-helium gas is developed which consists of 30 steps over the spectral range of 0 to 20 eV. By employing this model, results were obtained for temperature, pressure, density, the shock layer and along the body surface. These are compared with results of two sophisticated radiative transport models available in the literature.

Tiwari, S. N.↗
NASA NTRS1979

Some aspects of a free jet phenomena to 105 L/D in a constant area duct

Under certain conditions, inlets with a Borda type geometry were shown to exhibit sufficiently strong separation effects to permit the working fluid to flow through the duct as if it were a free jet. Mass limiting flow data and associated pressure profiles for tubes of 14, 53, 64, 73, and 105 L/D with a Borda type inlet were taken to determine bounds of the free jet phenomena. For a given tube roughness, the limits appear to be one dimensional and dependent only on inlet stagnation conditions. For smooth tubes the upper L/D boundary is related by P sub R roughly equal to CT to the 17th power and sub R, C roughly equal to 00017 (L/D) to the 2.5 power where F sub R = P/P sub c is reduced pressure and T sub R = T/T sub c is reduced temperature. The lower bound appears to be saturation conditions at the inlet. Similar free jet effects were found for fluid hydrogen indicating that fluid jetting may be common to all fluids. While limited data on surface roughness show a decrease in the upper L/D limit, nevertheless fluid jetting still occurred.

Hendricks, R. C.↗
NASA NTRS1979

Free jet phenomena in a 90 degree-sharp edge inlet geometry

Under certain conditions, inlets with a sharp edge or geometric corner were shown to exhibit sufficiently strong separation effects to permit the working fluid to flow through the duct as if it were a free jet. Mass limiting flow data and associated pressure profiles for tubes of 53, 64, 73, and 105 length/diameter with a 90 deg sharp edge or orifice type inlet were taken and compared to Borda type inlet data to determine bounds of the free jet phenomena. For smooth tubes the limits appear to be one dimensional and dependent only on inlet stagnation conditions. Similar free jet effects were found for fluid hydrogen indicating that fluid jetting may common to all fluids flowing through 90 deg sharp edge inlet geometries.

Hendricks, R. C.↗
NASA NTRS1978

Some flow phenomena in a constant area duct with a Borda type inlet including the critical region

Mass limiting flow characteristics for a 55 L/D tube with a Borda type inlet have been assessed over large ranges of temperature and pressure using fluid nitrogen. Under certain conditions, separation and pressure drop at the inlet was sufficiently strong to permit partial vaporization and the remaining fluid flowed through the tube as if it were a free jet. An empirical relation was determined which defines conditions under which this type of flow can occur. A flow coefficient is presented which enables one to estimate flow rates over the experimental range. A flow rate stagnation pressure map for selected stagnation isotherms and pressure profiles document these flow phenomena.

Hendricks, R. C.↗
NASA NTRS1979

Higher-order skewness and excess coefficients of some probability distributions applicable to optical propagation phenomena

Expressions are derived for higher-order skewness and excess coefficients using central moments and cumulants up to 8th order. These coefficients are then calculated for three probability distributions: (1) Log-normal, (2) Rice-Nakagami, and (3) Gamma distributions. Curves are given to shown the variation of skewness with excess coefficients for these distributions. These curves are independent of the particular distribution parameters. This method is useful for studying fluctuating phenomena, which obey non-Gaussian statistics.

Majumdar, A. K.↗
NASA NTRS1979

Mars atmospheric phenomena during major dust storms, as measured at surface

Meteorological instrumentation aboard the Viking Mars Landers measures wind, temperature, and pressure. Two global dust storms occurred during northern autumn and winter, observed both by the orbiters and by the landers. The meteorological data from the landers has been analyzed for the period just before first storm arrival to just after second storm arrival, with the objectives of defining the meteorological phenomena during the storm period, determining those associated with storm and dust arrival, and evaluating the effects on synoptic conditions and the general circulation. Times of dust arrival over the sites could be defined fairly closely from optical and pressure (solar tide) data, and dust arrival was also accompanied by changes in diurnal temperature range, temperature maxima, and temperature minima. The arrivals of the storms at Viking Lander 1 were accompanied by significant increases in wind speed and pressure. No such changes were observed at Viking Lander 2. It is possible that surface material could have been raised locally at Viking Lander 1. Throughout the period except for the time following the second dust storm the synoptic picture at Viking Lander 2 was one of eastward moving cyclonic and anticyclonic systems. These disappeared following the second storm, a phenomenon which may be related to the storm.

Ryan, J. A.↗
NASA NTRS1979

Effects of probe shape change on flow phenomena during Jovian entry

The effects of probe shape change on the flow phenomena around a Jovian entry body is investigated. The initial body shapes considered are: 45-degree sphere cone, 35-degree hyperboloid, and 45-degree ellipsoid. The radiating shock-layer flow is assumed to be axisymmetric, inviscid, and in chemical and local thermodynamic equilibrium. The radiative transfer is calculated with an existing nongray radiation model that accounts for molecular band, atomic line, and continuum transitions. The results indicate that the shock-standoff distance, shock temperature and density, wall pressure distribution and radiative heating to the body are influenced significantly because of the probe shape change. The effect of shape change on radiative heating of the afterbody was considerably larger for the sphere cone and ellipsoid than for the hyperboloid. For the peak heating conditions, the net radiative heating to the body was found to be highest for the ellipsoid

Tiwari, S. N.↗