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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 1,567 records · Page 87
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Coherent Doppler Lidar Data Products from Space-Based Platforms

Coherent Doppler lidar is a promising technique for the global measurements of winds using a space-based platform. Doppler lidar produces estimates of the radial component of the velocity vector averaged over the resolution volume of the measurement. Profiles of the horizontal vector winds are produced by scanning the lidar beam or stepping the lidar beam through a sequence of different angles (step-stare). The first design for space-based measurements proposed a conical scan which requires a high power laser to produce acceptable signal levels for every laser pulse. Performance is improved by fixing the laser beam and accumulating the signal from many lidar pulses for each range-gate. This also improves the spatial averaging of the wind estimates and reduces the threshold signal energy required for a good estimate. Coherent Doppler lidar performance for space-based operation is determined using computer simulations and including the wind variability over the measurement volume as well as the variations of the atmospheric aerosol backscatter.

Frehlich, Rod↗
NASA NTRS2003

Transient Relativistically-Shifted Lines as a Probe of Black Hole Systems

X-ray spectra of Seyfert-type Active Galaxies have revealed a new type of X-ray spectral feature, one which appears to offer important new insight into the black hole system. XMM revealed several narrow emission lines redward of Fe Kalpha in NGC 3516. Since that discovery in NGC 3516, the phenomenon has been observed in other Seyfert galaxies, e.g. NGC 7314 and ESO 198-G24. We present new evidence for a redshifted Fe line in XMM spectra of Mrk 766. These data reveal the first evidence for a significant shift in the energy of a redshift Fe line, the shift occurs over just a few tens of kiloseconds. This shift may be interpreted as deceleration of ejected gas, the velocity of the material lies just above the escape velocity at the implied radial location of the emitter.

Turner, T. J.↗
DOE OSTI2024

Wall modes and the transition to bulk convection in rotating Rayleigh-Bénard convection

We investigate states of rapidly rotating Rayleigh-Bénard convection in a cylindrical cell over a range of Rayleigh numbers 3 × 10 5 ≤ Ra ≤ 5 × 10 9 and Ekman numbers 10 − 6 ≤ Ek ≤ 10 − 4 for Prandtl number Pr = 0.8 and aspect ratios 1 / 5 ≤ Γ ≤ 5 using direct numerical simulations. We characterize, for perfectly insulating sidewall boundary conditions, the first transition to convection via wall mode instability and the nonlinear growth and instability of the resulting wall mode states, including a secondary transition to time dependence. We show how the radial structure of the vertical velocity u z and the temperature T is captured well by the linear eigenfunctions of the wall mode instability where the radial width of u z is δ u z ∼ Ek 1 / 3 r / H whereas δ T ∼ e − k r ( k is the wave number of a laterally infinite wall mode state). The disparity in spatial scales for Ek = 10 − 6 means that the heat transport is dominated by the radial structure of u z since T varies slowly over the radial scale δ u z . We further describe how the transition to a state of bulk convection is influenced by the presence of the wall mode states. We use temporal and spatial scales as measures of the local state of convection and the Nusselt number Nu as representative of global transport. Our results elucidate the evolution of the wall state of rotating convection and confirm that wall modes are strongly linked with the boundary zonal flow being the robust remnant of nonlinear wall mode states. We also show how the heat transport ( Nu ) contributions of wall modes and bulk modes are related and discuss approaches to disentangling their relative contributions. Published by the American Physical Society 2024

58 GEOSCIENCES↗
NASA NTRS1991

Descriptions of the neutral gas outflow in Comets P/Halley and Wilson (1987 VII) from analyses of velocity-resolved H2O line profiles

The spatial distribution and expansion velocity of the Comets Wilson (1987 VII) and pre- and postperihelion P/Halley are derived on the bases of velocity-resolved H2O spectral line profiles, using a kinematic model which synthesizes line profiles for comparison with observed line shapes. The results thus obtained demonstrate that the spherically symmetric outflow at constant velocity is a poor characterization of cometary neutral-gas outflow. While the radial dependence of the H2O expansion velocity is noted to be consistent with theoretically envisioned trends, the high H2O outflow velocity observed in Comet Wilson resists reconciliation with any existing kinematic model.

Larson, Harold P.↗
NASA NTRS1984

Impact experiments in viscous fluid media

Available phase and group velocity data are inverted by a procedure which includes the effects of transverse anisotropy, anelastic dispersion, sphericity, and gravity. The resulting models, for average Earth, average ocean, and oceanic regions divided according to the age of the ocean floor, are quite different from previous results which ignore the above effects. The models show a low-veocity zone with age dependent anisotropy and velocities higher than derived in previous surface wave studied. The correspondence between the anisotropy variation with age and a physical model based on flow aligned olivine is suggestive. For most of the Earth SHSV in the vicinity of the low-velocity zone. Near the East Pacific Rise, however, SVSH at depth, consistent with ascending flow. Anisotropy is as important as temperature in causing radial and lateral variations in velocity. The models have a high velocity nearly isotropic layer at the top of the mantle that thickens with age. This layer defines the LID, or seismic lithosphere. In the Pacific, the LID thickens with age to a maximum thickness of about 50 km. This thickness is comparable to the thickness of the elastic lithosphere. The LID thickness is thinner than derived using isotropic or pseudo-isotropic procedures A new model for Average Earth is obtained which includes a thin LID. This model extends the fit of a P.R.E.M. type model to shorter period surface waves.

Greeley, R.↗
NASA NTRS1976

The August 1972 solar-terrestrial events - Interplanetary magnetic field observations

Interplanetary-magnetic-field measurements made by Pioneers 9 and 10, HEOS 2, and Explorer 41 during early August 1972 are reviewed. It is noted that the two Pioneers were nearly radially aligned during the flare events, with Pioneer 9 at a distance of 0.78 AU from the sun and Pioneer 10 at a distance of 2.2 AU. The data obtained by Pioneer 9, Pioneer 10, and the two near-earth satellites are analyzed separately, and the major flare-associated shocks are identified. An attempt is made to identify corresponding shocks at the different locations and to determine their propagation velocities in the region between 0.8 and 2.2 AU. It is found that there was an obvious tendency for the average shock velocities to decrease with increasing radial distance from the sun and that the local velocities at the Pioneer locations were significantly smaller than the appropriate average values. A comparison of these local velocities indicates that there was a large deceleration of the shocks between the sun and some distance within 0.8 AU but little, if any, deceleration beyond that distance. A plot of average shock velocities from the sun to 1.0 AU as a function of longitude separation between the flares and Pioneer 9 is shown to suggest a pronounced deviation of the shock fronts from spherical symmetry.

Smith, E. J.↗
NASA NTRS1957

Induced Velocities Near a Lifting Rotor with Nonuniform Disk Loading

A method is given for converting known uniformly loaded rotor induced velocities to correspond with arbitrary axisymmetric nonuniform disk load distributions. Numerical results for two specific distributions are given in chart form. Symmetry relations and relations between radial disk loading and wake velocities are developed. Experimental flow measurements are presented and compared with theory. Reasonable agreement is shown in the forward part of the flow when nonuniform loading is assumed, but far behind the rotor the flow is more like that of a wing.

Heyson, Harry H↗
NASA NTRS1990

Numerical modeling of an arcjet thruster

A numerical model of an arcjet thruster was developed and the results of calculations using this model are compared to the experimental data from a 30 kW arcjet using ammonia as a propellant. The model contains equations for the conservation of mass, radial, axial, and azimuthal momentum, energy, and the radial component of the magnetic field and provides a solution for three components of velocity, temperature, and the axial and radial current as a function of position in an axisymmetric flowfield. The model predicts 12 percent more specific impulse than the experiment when the mass flow and power input are constrained to the experimental values. A major conclusion of this study is that improved procedures for calculating transport properties are necessary if the accuracy of the model is to be improved.

Rhodes, Robert P.↗
DOE OSTI2022

Experimental measurements of fluid flow in an 84-pin hexagonal rod bundle with spacer grid for a gas-cooled fast modular reactor

A 50 MW e helium-cooled fast modular reactor (FMR) is under development, and as part of the Department of Energy Integrated Research Project (IRP), Texas A&M University is conducting the thermal-hydraulic characterization of its baseline core configuration. Here, we experimentally investigated the axial and cross flow fields characteristics in the hexagonal fuel rod bundle composed of 84 rods, a central rod, and spacer grids at a Reynolds number of 12,000. A fully transparent experimental facility resembling of one unit of the fuel assembly was constructed. Time-resolved particle image velocimetry (TR-PIV) measurements were performed to characterize hydraulic behavior downstream the spacer grid. Velocity measurements were conducted in the axial and radial direction of the rod bundle. From the PIV velocity vector fields, the full-field flow statistics were computed for the mean velocity, vorticity, and Reynolds stresses. An analysis of the energy decay downstream of the spacer grid was conducted with calculations of secondary-flow intensities, turbulent kinetic energy, power spectrum, and spatial-temporal velocity cross correlations. The vorticity field was obtained and pairs of counter-rotating vortexes were identified using a 3D reconstruction of several measurement planes. The data from this experimental campaign will be used to validate numerical models based on Computational Fluid Dynamics and other codes.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS1981

Application of unsteady airfoil theory to rotary wings

A clarification is presented on recent work concerning the application of unsteady airfoil theory to rotary wings. The application of this theory may be seen as consisting of four steps: (1) the selection of an appropriate unsteady airfoil theory; (2) the resolution of that velocity which is the resultant of aerodynamic and dynamic velocities at a point on the elastic axis into radial, tangential and perpendicular components, and the angular velocity of a blade section about the deformed axis; (3) the expression of lift and pitching moments in terms of the three components; and (4) the derivation of explicit expressions for the components in terms of flight velocity, induced flow, rotor rotational speed, blade motion variables, etc.

Kaza, K. R. V.↗
NASA NTRS1972

Velocity diagrams

The selection and design of velocity diagrams for axial flow turbines are considered. Application is treated in two parts which includes: (1) mean-section diagrams, and (2) radial variation of diagrams. In the first part, the velocity diagrams occurring at the mean section are assumed to represent the average conditions encountered by the turbine. The different types of diagrams, their relation to stage efficiency, and their selection when staging is required are discussed. In the second part, it is shown that in certain cases the mean-section diagrams may or may not represent the average flow conditions for the entire blade span. In the case of relatively low hub- to tip-radius ratios, substantial variations in the velocity diagrams are encountered. The radial variations in flow conditions and their effect on the velocity diagrams are considered.

Whitney, W. J.↗
NASA NTRS2004

Impact Processes in the Solar System

Our laboratory has previously conducted impact fracture and dynamic failure tests. Polanskey and Ahrens [1990] mapped the fractures from a series of laboratory craters (Fig. 1) and Ahrens and Rubin [ 1993] inferred that the usually further extending radial cracks resulted from tensional failure during the compression of the shock propagation. The radial spreading induced by the particle velocity field caused the stresses perpendicular to the shock front to become sufficiently large and tensile. This induces "radial fractures." The concentric fractures are attributed to the tensional failure occurring after the initial compressive phase. Upon radial propagation of the stress wave the negative tension behind the stress-wave front caused failure along the quasi-spherical concentric fractures. The near-surface and spall fractures are attributed to the fractures described by Melosh [1984]. These are activated by impact and can launch relatively unshocked samples of planetary surfaces to speeds exceeding escape velocity. In the case of Mars, some of these surface samples presumably become the SNC (Mars) meteorites.

Ahrens, Thomas J.↗
NASA NTRS1979

Sunspots and the physics of magnetic flux tubes. III - Aerodynamic lift

The aerodynamic lift exerted on a magnetic flux tube by the asymmetric flow around the two sides of the tube is calculated as part of an investigation of the physics of solar flux tubes. The general hydrodynamic forces on a rigid circular cylinder in a nonuniform flow of an ideal fluid are derived from the first derivatives of the velocity field. Aerodynamic lift in a radial nonuniform flow is found to act in the direction of the flow, toward the region of increased flow velocity, while in a shear flow, lift is perpendicular to the free stream and directed toward increasing flow velocity. For a general, three dimensional, large-scale stationary incompressible equilibrium flow, an expression is also derived relating the lift per unit length to the dynamical pressure, cylinder radius and the gradient of the free-stream velocity. Evidence from an asymmetric airfoil in a uniform flow indicates that lift is enhanced in a real fluid in the presence of turbulence.

Parker, E. N.↗
NASA NTRS1974

A technique for generating shear waves in cylindrical shells under radial impact

Experimental techniques are developed to study and measure the shear-wave velocity in an aluminum cylindrical shell subjected to a radial impact. The radial impact is obtained by exploding an electrical detonator inserted in plastic plugs mounted on the end of the shell. Strain gages, mounted on the outside surface of the shell at various axial locations, are used to obtain oscilloscope traces from which the shear-wave velocity can be calculated.

Blum, A.↗
NASA NTRS1977

Revised FORTRAN program for calculating velocities and streamlines on the hub-shroud midchannel stream surface of an axial-, radial-, or mixed-flow turbomachine or annular duct. 1: User's manual

A FORTRAN 4 computer program was developed that obtains a detailed subsonic or shock-free transonic flow solution on the hub-shroud midchannel stream surface of a turbomachine. The blade row may be fixed or rotating, and the blades may be twisted and leaned. Flow may be axial, mixed, or radial. Upstream and downstream flow variables may vary from hub to shroud, and provision is made to correct for loss of stagnation pressure. The results include velocities, streamlines, and flow angles on the stream surface as well as approximate blade surface velocities. Subsonic solutions are obtained by a finite-difference, stream-function solution. Transonic solutions are obtained by a velocity-gradient method that uses information from a finite-difference, stream-function solution at a reduced mass flow.

Katsanis, T.↗
NASA NTRS1977

Revised FORTRAN program for calculating velocities and streamlines on the hub-shroud midchannel stream surface of an axial-, radial-, or mixed-flow turbomachine or annular duct. 2: Programmer's manual

A FORTRAN IV computer program has been developed that obtains a detailed subsonic or shock free transonic flow solution on the hub-shroud midchannel stream surface of a turbomachine. The blade row may be fixed or rotating, and the blades may be twisted and leaned. Flow may be axial, mixed, or radial. Upstream and downstream flow variables may vary from hub to shroud, and provisions are made to correct for loss of stagnation pressure. The results include velocities, streamlines, and flow angles on the stream surface and approximate blade surface velocities.

Katsanis, T.↗