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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 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Test and evaluation of water vapor radiometers

The accuracy of very long baseline interferometry in geodetic and astrometric applications is primarily limited by the propagation delays through the troposphere. The part of this delay that is most difficult to predict is due to atmospheric water vapor which can contribute up to about 40 cm of excess propagation path at microwave frequencies. The water vapor content in the atmosphere is variable and is not well correlated with surface meteorological variables. The brightness temperature measured near the transition of water vapor at 22.2 GHz and the propagation delay due to water vapor, or wet path length, are well correlated. This correlation is not perfect because the absorption coefficient and index of refraction do not have the same dependence on temperature and pressure.

Moran, J.↗
NASA NTRS1981

Effects of solid particles suspended in fluid flow through an axial flow compressor stage

An approximate method for calculating the flow properties of gas-particle mixture flowing over blades in a cascade is studied. Using an analytical method, the solid particle trajectory and location of collisions between the solid particles and the blade surfaces are determined. In addition an experimental investigation of the trajectories and velocities of solid particles suspended in a fluid passing through an axial flow compressor cascade was performed. The cascade blades were made of 2024 aluminum alloy and the solid particles used were quartz sand with average diameter of 165 microns. The following parameters were investigated: blade pressure distribution, and total pressure loss coefficient, both depending on the degree of erosion. In addition, a theoretical estimation of the blade erosion is compared with the experimental data.

Tabakoff, W.↗
NASA NTRS1981

Basic lubrication equations

Lubricants, usually Newtonian fluids, are assumed to experience laminar flow. The basic equations used to describe the flow are the Navier-Stokes equation of motion. The study of hydrodynamic lubrication is, from a mathematical standpoint, the application of a reduced form of these Navier-Stokes equations in association with the continuity equation. The Reynolds equation can also be derived from first principles, provided of course that the same basic assumptions are adopted in each case. Both methods are used in deriving the Reynolds equation, and the assumptions inherent in reducing the Navier-Stokes equations are specified. Because the Reynolds equation contains viscosity and density terms and these properties depend on temperature and pressure, it is often necessary to couple the Reynolds with energy equation. The lubricant properties and the energy equation are presented. Film thickness, a parameter of the Reynolds equation, is a function of the elastic behavior of the bearing surface. The governing elasticity equation is therefore presented.

Hamrock, B. J.↗
NASA NTRS1982

Aerosound from corner flow and flap flow

Noise generation at the edge of a wing flap is analyzed. The phenomenon as a single vortex moving around a corner in an incompressible, potential flow is modelled. Vortex image retarding effects are proposed as an explanation for small Strouhal numbers. The model surface pressures, sound pressures (using Curle's theory), and Mach number dependencies agree with wind tunnel experiments. A double pressure peak is found in the model (credited to image action) which is qualitatively similar to measured sound correlations. Incompressible flow aerosound calculations are discussed. The effects of a series of vortices moving in the same idealized potential flow are also studied. The vortices are assumed to be statistically independent so their intensities can be added. The frequency of appearance of the vortices are determined from measurements. Diffraction effects caused by the presence of the wing near the dipole sound radiators on the flap surfaces are included.

Meecham, W. C.↗
NASA NTRS1983

Nonlinear interactions in superfluid dynamics: Nonstationary heat transfer due to second sound shock waves

Second sound techniques were used to study superfluid helium. Second sound shock waves produced relative velocities in the bulk fluid. Maximum counterflow velocities produced in this way are found to follow the Langer-Fischer prediction for the fundamental critical velocity in its functional dependence on temperature and pressure. Comparison of successive shock and rotating experiments provides strong evidence that breakdown results in vorticity production in the flow behind the shock. Schlieren pictures have verified the planar nature of second sound shocks even after multiple reflections. The nonlinear theory of second sound was repeatedly verified in its prediction of double shocks and other nonlinear phenomena.

Liepmann, H. W.↗
NASA NTRS1983

Magnetism and thermal evolution of the terrestrial planets

The absence in the cases of Venus and Mars of the substantial intrinsic magnetic fields of the earth and Mercury is considered, in light of thermal history calculations which suggest that, while the cores of Mercury and the earth are continuing to freeze, the cores of Venus and Mars may still be completely liquid. It is noted that completely fluid cores, lacking intrinsic heat sources, are not likely to sustain thermal convection for the age of the solar system, but cool to a subadiabatic, conductive state that cannot maintain a dynamo because of the gravitational energy release and the chemically driven convection that accompany inner core growth. The models presented include realistic pressure- and composition-dependent freezing curves for the core, and material parameters are chosen so that correct present-day values of heat outflow, upper mantle temperature and viscosity, and inner core radius, are obtained for the earth.

Stevenson, D. J.↗
NASA NTRS1983

Multicolor laser altimeter for barometric measurements over the ocean - Theoretical

It is noted that the optical path length from a satellite to the earth's surface strongly depends on the atmospheric pressure along the propagation path. The theoretical basis of a surface pressure measurement technique, which uses a two-color laser altimeter to observe the change with wavelength in the optical path length from a satellite to the ocean surface, is evaluated. The statistical characteristics of the ocean-reflected pulses and the expected measurement accuracy are analyzed in terms of the altitude parameters. The results show that it is feasible to obtain a pressure accuracy of a few millibars.

Gardner, C. S.↗
NASA NTRS1987

Structural tailoring using the SSME/STAEBL code

Space Shuttle Main Engine/Structural Tailoring of Engine Blades (SSME/STAEBL) was developed by systematically modifying and enhancing the STAEBL code developed by Pratt and Whitney under contract to NASA Lewis Research Center. STAEBL was designed for application to gas turbine blade design. Typical design variables include blade thickness distribution and root chord. Typical constraints include resonance margins, root stress, and root to chord ratios. In this program, the blade is loaded by centrifugal forces only. Additions and modifications of STAEBL included in SSME/STAEBL include (1) thermal stress analysis; (2) gas dynamic (pressure) loads; (3) temperature dependent material and thermal properties; (4) forced vibrations; (5) tip displacement constraints; (6) single crystal material analysis; (7) blade cross section stacking offsets; and (8) direct time integration algorithm for transient dynamic response. Capabilities are also included which permit data transfer from finite element models and stand-alone analysis.

Rubinstein, Robert↗
NASA NTRS1987

Inerting and atmospheres

It is argued that fires are dependent primarily on the concentration of oxygen, whereas life is dependent on the partial pressure of oxygen. It follows that in an inhabited capsule it should be possible to exercise a certain amount of willful control over fire and still maintain habitability by proper selection of the composition of the atmosphere. This leads to two concepts in the control of fires in confined spaces by controlling atmospheric composition: the first, to lower the overall potential hazard by maintaining the percent of oxygen in the capsule below that of air, and second, to provide for the emergency extinguishment of a fire by sudden flooding with nitrogen. Several relevant charts and graphs are presented.

Carhart, Homer W.↗
NASA NTRS1987

Performance test of a laboratory pump liquid transfer based on the fountain effect

A laboratory scale pump has been tested in detail in order to determine the flow characteristics of a heater-activated all-metal thermomechanical pump (fountain effect pump, FEP). The emphasis is on the functional dependence of the fountain pressure difference versus mass throughput. A modified Vote et al. (1971) power law approximation is employed for a simplified description of the flow rate as a function of the driving force. Flow rates of up to 10 liters/(hr/sq cm) have been obtained despite a large nominal pore size of the porous plug of 2 microns (filtration rating) used for the FEP.

Chen, W. E. W.↗
NASA NTRS1988

Performance test of a laboratory pump for liquid transfer based on the fountain effect

A laboratory scale pump which determines the flow characteristics of a heater-activated all-metal thermomechanical fountain-effect pump (FEP) is evaluated. Results are presented on the functional dependence of the fountain pressure difference versus mass throughput. A modified Vote et al. (1971) power law approximation is used to obtain the flow rate as a function of the driving force. Despite a large nominal pore size of the porous plug used for the FEP, flow rates of up to 10 liter/hr sq cm have been obtained.

Chen, W. E. W.↗
NASA NTRS1988

Aerodynamic pressures and heating rates on surfaces between split elevons at Mach 6.6

An aerothermal study was performed in the Langley 8-Foot High Temperature Tunnel at Mach number 6.6 to define the pressures and heating rates on the surfaces between split elevons similar to those used on the Space Shuttle. Tests were performed with both laminar and turbulent boundary layers on the wing surface upstream of the elevons. The flow in the chordwise gap between the elevons was characterized by flow separation at the gap entrance and flow reattachment at a depth into the gap inversely proportional to the gap width. The gap pressure and heating rate increased significantly with decrease of elevon gap width, and the maximum gap heating rate was proportional to the maximum gap pressure. Correlation of the present results indicate that the gap heating was directly proportional to the elevon windward surface pressure and was not dependent upon whether the boundary layer on the windward elevon surface was laminar or turbulent.

Hunt, L. Roane↗
NASA NTRS1990

Requirements for long-life operation of inert gas hollow cathodes: Preliminary report

An experimental investigation was initiated to establish conditioning procedures for reliable hollow cathode operation via the characterization of critical parameters in a representative cathode test facility. From vacuum pumpdown rates, it was found that approximately 1.5 hours were required to achieve pressure levels within 5 percent of the lowest attainable pressure for this facility, depending on the purge conditions. The facility atmosphere was determined by a residual gas analyzer to be composed of primarily air and water vapor. The effects of vacuum pumping and inert gas purging were evaluated. A maximum effective leakage rate of 2.0 x 10(exp -3)sccm was observed and its probable causes were examined. An extended test of a 0.64 cm diameter Mo-Re hollow cathode was successfully completed. This test ran for 504 hours at an emission current of 23.0 amperes and a xenon flow rate of 6.1 sccm. Discharge voltage rose continuously from 15 to 21 volts over the course of the test. The temperature of the cathode body during the test was relatively stable at 1160 C. Post-test examination revealed ion-bombardment texturing of the orifice plate to be the only detectable sign of wear on the hollow cathode.

Verhey, Timothy R.↗
NASA NTRS1989

Photochemistry of CO and H2O - Analysis of laboratory experiments and applications to the prebiotic earth's atmosphere

The role photochemical reactions in the early earth's atmosphere played in the prebiotic synthesis of simple organic molecules was examined, extending an earlier calculation of formaldehyde production rates to more reduced carbon species, such as methanol, methane, and acetaldehyde. The experimental results of Bar-Nun and Chang (1983) are simulated as an aid in the construction of the photochemical scheme and as a way of validating the model. The results indicate that some fraction of CO2 and H2 present in the primitive atmosphere could have been converted to simple organic molecules. The exact amount is dependent on the partial pressure of CO2 and H2 in the atmosphere and on what assumptions are made concerning the shape of the absorption spectra of CO2 and H2O.

Wen, Jun-Shan↗
NASA NTRS1990

Requirements for long-life operation of inert gas hollow cathodes - Preliminary results

An experimental investigation was initiated to establish conditioning procedures for reliable hollow cathode operation via the characterization of critical parameters in a representative cathode test facility. From vacuum pumpdown rates, it was found that approximately 1.5 hours were required to achieve pressure levels within 5 percent of the lowest attainable pressure for this facility, depending on the purge conditions. The facility atmosphere was determined by a residual gas analyzer to be composed of primarily air and water vapor. The effects of vacuum pumping and inert gas purging were evaluated. A maximum effective leakage rate of 2.0 x 10 (exp -3) sccm was observed and its probable causes were examined. An extended test of a 0.64 cm diameter Mo-Re hollow cathode was successfully completed. This test ran for 504 hours at an emission current of 23.0 amperes and a xenon flow rate of 6.1 sccm. Discharge voltage rose continuously from 15 to 21 volts over the course of the test. The temperature of the cathode body during the test was relatively stable at 1160 C. Post-test examination revealed ion-bombardment texturing of the orifice plate to be the only detectable sign of wear on the hollow cathode.

Verhey, Timothy R.↗
NASA NTRS1990

Hybrid laminar flow control tests in the Boeing Research Wind Tunnel

The hybrid laminar flow control (HLFC) concept has undergone wind tunnel testing at near full-scale Reynolds number on an infinite wing of 30-deg sweep on which boundary-layer suction was furnished over the first 20 percent of chord of the upper surface. Depending on the external pressure distribution, the HLFC extended the laminarity of the boundary layer as far back as 45 percent of chord; this corresponds to a transition Reynolds number of about 11 million. The maximum chordwise extent of laminar run was found to be insensitive to the suction level over a wide range.

Parikh, P. G.↗
NASA NTRS1992

Propagation velocity and space-time correlation of perturbations in turbulent channel flow

A database obtained from direct numerical simulation of a turbulent channel flow is analyzed to extract the propagation velocity V of velocity, vorticity, and pressure fluctuations from their space-time correlations. A surprising result is that V is approximately the same as the local mean velocity for most of the channel, except for the near-wall region. For y(+) is less than or equal to 15, V is virtually constant, implying that perturbations of all flow variables propagate like waves near the wall. In this region V is 55 percent of the centerline velocity U(sub c) for velocity and vorticity perturbations and 75 percent of U(sub c) for pressure perturbations. Scale-dependence of V is also examined by analyzing the bandpass filtered flow fields. Comprehensive documentation of the propagation velocities and space-time correlation data, which should prove useful in the evaluation of Taylor's hypothesis is presented. An attempt was made to explain some of the data in terms of our current understanding of organized structures, although not all of the data can be explained this way.

Kim, John↗