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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Calibrator tests of heat flux gauges mounted in SSME blades

Measurements of heat flux to space shuttle main engine (SSME) turbine blade surfaces are being made in the Lewis heat flux calibration facility. Surface heat flux information is obtained from transient temperature measurements taken at points within the gauge. A 100-kW Vortek arc lamp is used as a source of thermal radiant energy. Thermoplugs, with diameters of about 0.190 cm and lengths varying from about 0.190 to 0.320 cm, are being investigated. The thermoplug is surrounded on all surfaces except the active surface by a pocket of air located in the circular annulus and under the back cover. Since the thermoplug is insulated, it is assumed that heat is conducted in a one-dimensional manner from the hot active surface to the cooler back side of the thermoplug. It is concluded that the miniature plug-type gauge concept is feasible for measurement of blade surface heat flux. It is suggested that it is important to measure heat flux near the hub on the suction surface and at the throat on SSME blades rotating in engines because stress and heat transfer coefficients are high in this region.

Liebert, Curt H.↗
NASA NTRS1991

Liquid atomization by coaxial rocket injectors

The atomization characteristics of a scaled-down version of a coaxial rocket injector was investigated using a phase Doppler particle analyzer (PDPA). The injector was operated in the conventional mode with liquid being injected through its inner orifice and gas being injected through its outer annulus. The shearing action occurring at the liquid-gas interface causes the liquid jet to atomize. In this study, two different liquid-air systems, namely a water-air system and a liquid nitrogen-gaseous nitrogen system, were chosen for detailed investigation. This paper discusses the performance characteristics of the coaxial injector under different flow and geometric conditions. Specifically, the effects of injection gas pressure and the injector cavity size on variables such as the mean particle diameter, Sauter mean diameter, number density, volume flux, and velocity have been presented.

Sankar, S. V.↗
NASA NTRS1991

Fluid-structure interaction forces at pump-impeller-shroud surfaces for axial vibration analysis

The axial forces developed on a pump impeller shroud surfaces are analyzed using a bulk-flow model of the leakage path between the impeller and the housing. Shear stresses at the impeller and the housing surfaces are modeled according to Hirs's turbulent lubrication model. The calculated results yield predictions of resonance peaks of the fluid within the annulus formed by the impeller shroud and housing. Numerical results are presented for a double-suction single-stage pump, showing that the direct stiffness of the perturbed impeller shroud forces is negligible; the forces become important only for pumps with very low axial natural frequencies in comparison to the running speed.

Childs, D. W.↗
NASA NTRS1991

Flow visualization of a rocket injector spray using gelled propellant simulants

A study was conducted at NASA-Lewis to compare the atomization characteristics of gelled and nongelled propellant simulants. A gelled propellant simulant composed of water, sodium hydroxide, and an acrylic acid polymer resin (as the gelling agent) was used to simulate the viscosity of an aluminum/PR-1 metallized fuel gel. Water was used as a comparison fluid to isolate the rheological effects of the water-gel and to simulate nongelled RP-1. The water-gel was injected through the central orifice of a triplet injector element and the central post of a coaxial injector element. Nitrogen gas flowed through the outer orifices of the triplet injector element and through the annulus of the coaxial injector element and atomized the gelled and nongelled liquids. Photographs of the water-gel spray patterns at different operating conditions were compared with images obtained using water and nitrogen. A laser light was used for illumination of the sprays. The results of the testing showed that the water sprays produced a finer and more uniform atomization than the water-gel sprays. Rheological analysis of the water-gel showed poor atomization caused by high viscosity of water-gel delaying the transition to turbulence.

Green, James M.↗
NASA NTRS1991

Morphology and evolution of coronae and ovoids on Venus

Coronae and ovoids on Venus were first identified in Venera 15/16 data. They are distinctive and apparently unique to the planet, and may be important indicators of processes operating in the Venusian mantle. Magellan images have provided the first high resolution views of coronae and ovoid morphology. Herein, the general geologic character is described of coronae and ovoids, and some inferences are drawn about their geologic evolution. Coronae are circular to elongate features surrounded by an annulus of deformational features, with a relatively raised or indistinct topographic signature and, commonly, a peripheral trough or moat. Ovoids are circular to elongate features other than coronae with either positive or negative topographic signatures, associated with tectonic deformation and volcanism. The relationship of these two geologic features to each other and to Venusian geology is briefly discussed.

Squyres, Steven W.↗
NASA NTRS1991

Radar backscattering by the icy Galilean satellites and the radar glory effect

Radar echoes from the icy Galilean satellites are unique in character and they may be explained by a phenomenon that was called the radar glory effect. The radar glory backscattering from buried craters was analyzed as a possible model for this effect. These craters have a smaller refractive index below the crater than above. The possibility exists that the rays will be totally internally reflected at the crater walls. The rays which contribute to the backscattering will come from a circular annulus, when viewed before the refraction occurs at the ice-vacuum surface, in a plane orthogonal to the rays reflected from the crater.

Gurrola, Eric M.↗
NASA NTRS1991

Velocity and pressure characteristics of a model SSME high pressure fuel turbopump

Under the present effort an experiment rig has been constructed, an instrumentation package developed and a series of mean and rms velocity and pressure measurements made in a turbopump which modelled the first stage of the Space Shuttle Main Engine (SSME) High Pressure Fuel Turbopump. The rig was designed so as to allow initial experiments with a single configuration consisting of a bell-mouth inlet, a flight impeller, a vaneless diffuser and a volute. Allowance was made for components such as inlet guide vanes, exit guide vanes, downstream pumps, etc. to be added in future experiments. This flexibility will provide a clear baseline set of experiments and allow evaluation in later experiments of the effect of adding specific components upon the pump performance properties. The rotational speed of the impeller was varied between 4260 and 7680 rpm which covered the range of scaled SSME rotation speeds when due allowance is made for the differing stagnation temperature, model to full scale. The results at the inlet obtained with rotational speeds of 4260, 6084 and 7680 rpm showed that the axial velocity at the bell-mouth inlet remained roughly constant at 2.2 of the bulk velocity at the exit of the turbopump near the center of the inlet, but it decreased rapidly with increasing radius at all three speeds. Reverse flow occurred at a radius greater than 0.9 R for all three speeds and the maximum negative velocity reduced from 1.3 of the bulk velocity at the exit of the turbopump at 4260 rpm to 0.35 at 7680 rpm, suggesting that operating at a speed closer to the design condition of 8700 rpm improved the inlet characteristics. The reverse flow caused positive prerotation at the impeller inlet which was negligibly small near the center but reached 0.7 of the impeller speed at the outer annulus. The results in the diffuser and the volute obtained at 7680 rpm show that the hub and shroud walls of the diffuser were characterized by regions of transient reverse flow with negative revolution-averaged velocity of 8 percent of the maximum forward revolution-averaged velocity at the center of the diffuser passage near the shroud wall.

Tse, D. G-N.↗
NASA NTRS1991

Analysis of radiative and phase-change phenomena with application to space-based thermal energy storage

The simplified geometry for the analysis is an infinite, axis symmetric annulus with a specified solar flux at the outer radius. The inner radius is either adiabatic (modeling Flight Experiment conditions), or convective (modeling Solar Dynamic conditions). Liquid LiF either contacts the outer wall (modeling ground based testing), or faces a void gap at the outer wall (modeling possible space based conditions). The analysis is presented in three parts: Part 3 considers and adiabatic inner wall and linearized radiation equations; part 2 adds effects of convection at the inner wall; and part 1 includes the effect of the void gap, as well as previous effects, and develops the radiation model further. The main results are the differences in melting behavior which can occur between ground based 1 g experiments and the microgravity flight experiments. Under 1 gravity, melted PCM will always contact the outer wall having the heat flux source, thus providing conductance from this source to the phase change front. In space based tests where a void gap may likely form during solidification, the situation is reversed; radiation is now the only mode of heat transfer and the majority of melting takes place from the inner wall.

Lund, Kurt O.↗
NASA NTRS1992

Computer code for preliminary sizing analysis of axial-flow turbines

This mean diameter flow analysis uses a stage average velocity diagram as the basis for the computational efficiency. Input design requirements include power or pressure ratio, flow rate, temperature, pressure, and rotative speed. Turbine designs are generated for any specified number of stages and for any of three types of velocity diagrams (symmetrical, zero exit swirl, or impulse) or for any specified stage swirl split. Exit turning vanes can be included in the design. The program output includes inlet and exit annulus dimensions, exit temperature and pressure, total and static efficiencies, flow angles, and last stage absolute and relative Mach numbers. An analysis is presented along with a description of the computer program input and output with sample cases. The analysis and code presented herein are modifications of those described in NASA-TN-D-6702. These modifications improve modeling rigor and extend code applicability.

Glassman, Arthur J.↗
NASA NTRS1992

Ultrasoft x ray bursts: A clue to the origin of gamma ray bursts?

A search was conducted for short timescale (less than or approx. 10 s) faint X ray bursts in the complete 201,000,000 photon Einstein Observatory imaging proportional counter (IPC) data base. Some 73,000,000 events were extracted which were distributed among 11,230 observing intervals with an average observing time of approx. 1400 seconds. To exclude all sources, only those spatial pixels were searched with a count rate less than 6 x 10(exp -4) counts/sec sq arcmin. The mean count rate was much less. All files with less than 400 secs of observing time were excluded. The data was then binned into overlapping cells 4'.3 by 4'.3 by 10 secs in volume, and all the space-time cells were searched to locate cells with more than 5 counts in a 10 sec interval; i.e., a minimum flux enhancement of 50 over the mean rate for that point in space. Some 52 such events were found. An annulus was inspected around the event to see if it coincided with a general rise in the counter's event rate. Ten events did coincide with counter phenomena; these were associated with sunrise, sunset, or the approach of the South Atlantic Anomaly and were excluded. The remaining 42 events were then examined in an attempt to associate them with instrumental or environmental artifacts. The event occurrence times are uniformly distributed over the course of the mission and show no correlation with local solar time; their positions are randomly distributed in geographic, Galactic, and celestial coordinates. Their summed radial distribution is consistent with the point response function of the IPC for a soft source, indicating that the events are focused by the Observatory's mirror system. The integrated spectrum is, indeed, quite soft and is very similar to that of the cataclysmic variable star U Gem in outburst. Most of the events have risetimes of less than or approx. 1 sec and decay times ranging from 1 to 20 sec. Their positions are not associated with any class of catalogued objects. Several possible origins are discussed for the events; if they are associated with gamma ray bursters, they provide interesting constraints on the space density and repetition rate of the underlying source population.

Helfand, D. J.↗
NASA NTRS1991

Numerical prediction of wakes in cascades and compressor rotors including the effects of mixing. II - Rotor passage flow and wakes including the effects of spanwise mixing

The results of a numerical investigation to predict the flow field including wakes and mixing in axial-flow compressor rotors are presented. The wake behavior in a moderately loaded compressor rotor is studied numerically using a 3D incompressible Navier-Stokes solver with a high Reynolds number form of a turbulence model. The equations are solved using a time dependent implicit technique. The agreement between the measured data and the predictions is good; including the blade boundary-layer profiles, wake mean-velocity profiles, and decay. The ability of the pseudocompressibility scheme to predict the entire flow field including the near and far wake profiles and its decay characteristics, effect of loading, and the viscous losses of a 3D rotor flow field are demonstrated. The mixing in the downstream regions away from the hub and annulus walls is dominated by wake diffusion. In regions away from the walls the radial mixing is predominantly caused by the transport of mass, momentum, and energy by the radial component of velocity in the wake.

Lakshminarayana, B.↗
NASA NTRS1991

Supercritical baroclinic disturbances under the influence of topography

An Eady model modified to include Ekman dissipation and sloping horizontal boundaries is used to investigate the nonlinear evolution of baroclinic waves in the presence of surface topography. The effectiveness of the topography to phase lock and equilibrate a given mode vs that of baroclinity to propagate and vacillate that mode is found to depend on the topographic height, its zonal structure, and the level of supercriticality. When topography is sinusoidal and of the same wavelength as the baroclinically most unstable mode, it induces a short-period amplitude modulation whose envelope represents the baroclinic evolution. The dynamics of this modulation is explored analytically. When the sinusoidal topography is of a longer zonal wavelength, a 'mixed' wave state persists with amplitude dominance shifting between the topographic mode and the baroclinic mode, depending on the relative strength of form drag and baroclinicity. Model results are also compared, in appropriate parameter limits, with near-resonance asymptotic results and annulus experiments.

Chou, Shih-Hung↗
NASA NTRS1992

Infrared observations and thermal models of the Beta Pictoris disk

Measurements of the flux from the central portion of the Beta Pic disk performed via photometry at 3.5-20 microns in 4- and 8-arcsec apertures are presented. The 10.1- and 20-micron measurements show an excess which is extended, with significant flux located in the annulus between 4- and 8-arcsec diameter centered on the star. Disk models are calculated to reproduce the ground-based IR data, IRAS fluxes, IRAS 60-micron scan profile widths, and optical scattered light distribution. The color temperature and angular scale of the disk are found to be inconsistent with emission from large ('blackbody') particles: most of the thermal emission originates from particles which are inefficient radiators, with sizes near 1 micron. A simple disk with a single power-law spatial distribution is inconsistent with the combined optical and IR data. The inner disk component represents a gross deficit of material relative to an inward extrapolation of the outer component.

Backman, D. E.↗
NASA NTRS1992

Natural convection between concentric spheres

A finite-difference solution for steady natural convective flow in a concentric spherical annulus with isothermal walls has been obtained. The stream function-vorticity formulation of the equations of motion for the unsteady axisymmetric flow is used; interest lying in the final steady solution. Forward differences are used for the time derivatives and second-order central differences for the space derivatives. The alternating direction implicit method is used for solution of the discretization equations. Local one-dimensional grid adaptation is used to resolve the steep gradients in some regions of the flow at large Rayleigh numbers. The break-up into multi-cellular flow is found at high Rayleigh numbers for air and water, and at significantly low Rayleigh numbers for liquid metals. Excellent agreement with previous experimental and numerical data is obtained.

Garg, Vijay K.↗
NASA NTRS1992

Venus volcanism: A global overview from Magellan data

A preliminary analysis of a global survey of Magellan data covering over 90 percent of the surface and designed to document the characteristics, location, and dimensions of all major volcanic features on Venus has revealed over 1660 landforms and deposits. These include over 550 shield fields (concentrations of small volcanos less than 20 km in diameter), 274 intermediate volcanos between 20 and 100 km diameter with a variety of morphologies, 156 large volcanos in excess of 100 km diameter, 86 calderalike structures independent of those associated with shield volcanos and typically 60-80 km in diameter, 175 coronae (annulus of concentric ridges or fractures), 259 arachnoids (inner concentric and outer radial network pattern of fractures and ridges), 50 novae (focused radial fractures forming stellate patterns), and 53 lava flood-type flow fields, and 50 sinuous lava channels (all of which are in excess of 10(exp 2)-10(exp 3) km in length). The near-global coverage of Magellan data analyzed in this study confirms and extends the results of earlier observations that showed that volcanism is a widespread and significant process on the surface of Venus for the period of time in the presently observed record (less than about the last one billion years).

Head, James W., III↗
NASA NTRS1992

Observables for anticipating tornadogenesis in mesocyclones

We seek to identify an observable for anticipating tornadogenesis in mesocyclones, because such tornadoes are characterized by particularly long life, long and wide path, and high wind speed. We associate tornadogenesis with the transition from a one-cell vortex to a two-cell vortex. In such a transition, 'insertion' of a virtually nonrotating, slowly recirculating core displaces that high-swirl-speed air which is rapidly ascending along a moist-adiabatic locus of thermodynamic states, to an annulus at small but finite distance from the axis of rotation. Such a transition, on a vastly larger lateral scale, is known to characterize intensification of a tropical storm to a typhoon. We examine analytically a quasisteady axisymmetric model of a four-part vortex structure consisting of a bulk potential vortex, near-ground inflow layer, 'eyewall', and 'eye'. We inquire whether such a four-part intense vortex, formed in convectively unstably stratified air, is self-sustaining. In particular, we inquire whether the vertical profile of the angular momentum at the periphery is a discriminant for identifying self-sustaining vortices.

Carrier, G.↗
NASA NTRS1993

Laboratory and theoretical models of planetary-scale instabilities and waves

Research work is proceeding in theoretical, numerical, and experimental geophysical fluid dynamics leading up to a reflight of the GFFC (Geophysical Fluid Flow Cell Experiment) on USML-2. The work is intended not only to generate ideas for future space experiments, but to provide fundamental results concerned with nonlinear and chaotic properties of thermal convection and baroclinic waves in terrestrial and planetary atmospheres. The major efforts are focussed on thermal convection in a rapidly rotating annulus relevant to Jovian atmospheric dynamics, and on the chaotic behavior of baroclinic waves relevant to the Earth's atmosphere. The approach, in preparation for USML-2, is primarily theoretical and numerical. Mechanistic process models are solved numerically in order to identify physical mechanisms that may be observed in the GFFC, and which are important in real geophysical applications. The results from numerical simulations of geophysical fluid flow (subject to rotation and stratification) are compared with previous GFFC experiments on Spacelab-3 and with existing and proposed terrestrial laboratory experiments of various types. Pattern recognition algorithms have been employed to generate low-dimensional descriptions of the highly nonlinear and turbulent numerical simulations. Such empirically truncated descriptions provide for simplified but robust physical interpretations of the dynamics, as well as yielding highly efficient computations of these chaotic flows.

Hart, John E.↗
NASA NTRS1993

Flex-Gears

Flex-Gears are being developed as an alternative to brushes and slip rings to conduct electricity across a rotating joint. Flex-Gears roll in the annulus of sun and ring gears for electrical contact while maintaining their position by using a novel application of involute gears. A single Flex-Gear is predicted to transfer up to 2.8 amps, thereby allowing a six inch diameter device, holding 30 Flex-Gears, to transfer over 80 amps. Semi-rigid Flex-Gears are proposed to decrease Flex-Gear stress and insure proper gear meshing.

Tsai, Lung-Wen↗