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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 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Turbulent drag reduction research at NASA Langley - Progress and plans

Prospective research efforts planned at NASA-Langley in view of results obtained to date in passive turbulent drag reduction experiments are discussed. It has been established that conventional flow-aligned riblets are effective even in the presence of a degree of flow inclination and pressure gradients, and at transonic speeds. No increase in net drag reduction is expected from nonconventional riblet geometries. Large eddy breakup devices promise drag reductions in the 8-15 percent range. Heat transfer-augmentation, noise-reduction, turboprop/fuselage interaction noise reduction, are other advantages expected from this line of research.

Wilkinson, S. P.↗
NASA NTRS1988

Nonlinear 3-D evolution of bounded kinetic Alfven waves due to shear flow and collisionless tearing instability

The three-dimensional nonlinear simulation of the evolution of a kinetic Alfven wave is presented for simple boundary conditions that resemble those of a discrete auroral breakup arc. The model used is a variant of the reduced megnetohydrodynamic description that includes, in addition, the important dispersive effect of electron inertia. It is found that with a 'generator' boundary condition corresponding to a current generator and a fully conducting 'load' boundary, the wave evolves three-dimensionally through a combination of shear flow and collisionless tearing mode instability.

Seyler, Charles E., Jr.↗
NASA NTRS1988

Marine gravity of the Southern Ocean and Antarctic margin from Geosat

Geosat altimeter data, collected from an orbit with a ground rack that repeated every 17 days and overlayed one of the 17-day Seasat ground tracks, were used to map the gravity field of the Southern Ocean and the continental margin of Antarctica. The combination of ascending an descending profiles produced a typical Geosat ground track spacing of 70 km at the equator, with the best coverage occurring between the latitudes of 60 and 72 deg in both the Northern and Southern hemispheres. The new data reveal many previously uncharted seamounts and fracture zones in the extreme Southern Ocean areas adjacent to Antarctica, showing the detailed gravity signatures of the passive and active continental margins of Antarctica. Seven large age-offset fracture zones apparent in the Geosat data record the early breakup of Gondwana.

Sandwell, David T.↗
NASA NTRS1988

Fluid spray simulation with two-fluid nozzles

Two-phase interacting flow inside a two-fluid fuel atomizer was investigated and a correction of aerodynamic and liquid-surface forces with characteristic drop diameter was obtained for liquid-jet breakup in Mach 1 gas flow. Nitrogen gas mass-flux was varied from 6 to 50 g/sq cm sec by using four differently sized two-fluid atomizers with nozzle diameters varyig from 0.32 to 0.56 cm. The correlation was derived by using the acoustic gas velocity, V sub c, as a basic parameter in defining and evaluating the dimensionless product of the Weber (We) and Reynolds (Re) numbers. By using the definition of WeRe, it was found that the ratio of orifice diameter to Sauter mean drop diameter could be correlated with the dimensionless ratio WeRe and the gas to liquid density ratio.

Ingebo, Robert D.↗
NASA NTRS1988

Controlled reentry of the Gamma Ray Observatory (GRO)

Reentry of the GRO satellite must be controlled because it is expected that a great portion of the massive spacecraft would survive the reentry into the earth's atmosphere with the debris possibly causing harm to human life and property. The intent of this paper is to present a technique, results, and conclusion for a controlled reentry scenario for GRO. The planned impact would occur in an uninhabited portion of the South Pacific Ocean. Two major areas were analyzed. First, targeting analysis examined conditions under which the orbital maneuver study was done. Finally, the debris scatter involved analyzing effects of the breakup of the spacecraft on the impact area. These two areas were the basis from which the controlled reentry study was accomplished.

Brown, Evette R.↗
NASA NTRS1988

Investigation of spray dispersion and particulate formation in diesel fuel flames

An experimental study of electrostatical atomized and dispersed diesel fuel jets was conducted at various back pressures to 40 atm. A new electrostatic injection technique was utilized to generate continuous, stable fuel sprays at charge densities of 1.5 to 2.0 C/m3 of fluid at one atm, and about 1.0 C/m3 at 40 atm. Flowrates were varied from 0.5 to 2.5 ml/s and electric potentials to -18 kV. Visual observations showed that significant enhanced dispersion of charged fuel jets occurred at high back pressures compared to aerodynamic breakup and dispersion. The average drop size was about the same as the spray triode orifice diameter, and was between the Kelly theory and the Rayleigh limit. The ignition tests, done only at one atm, indicated stable combustion of the electrostatically dispersed fuel jets.

Back, L. H.↗
NASA NTRS1988

Remote sensing of ocean color in the Arctic

The main objectives of the research are: to increase the understanding of biological production (and carbon fluxes) along the ice edge, in frontal regions, and in open water areas of the Arctic and the physical factors controlling that production through the use of satellite and aircraft remote sensing techniques; and to develop relationships between measured radiances from the Multichannel Aircraft Radiometer System (MARS) and the bio-optical properties of the water in the Arctic and adjacent seas. Several recent Coastal Zone Color Scanner (CZCS) studies in the Arctic have shown that, despite constraints imposed by cloud cover, satellite ocean color is a useful means of studying mesoscale physical and biological oceanographic phenomena at high latitudes. The imagery has provided detailed information on ice edge and frontal processes such as spring breakup and retreat of the ice edge, influence of ice on ice effects of stratification on phytoplankton production, river sediment transport, effects of spring runoff, water mass boundaries, circulation patterns, and eddy formation in Icelandic waters and in the Greenland, Barents, Norwegian, and Bering Seas.

Maynard, N. G.↗
NASA NTRS1989

Preliminary measurements of auroral energy deposition and middle atmosphere electrodynamic response during MAC/Epsilon

On the nights of October 21 and 28, 1987 (UT), two Nike Orion payloads (NASA 31.066 and 31.067) were launched from Andoya, Norway, as part of the MAC/Epsilon campaign, to study auroral energetics and their effect on the middle atmosphere. Each payload carried instrumentation to measure relativistic electrons from 0.1 to 1.0 MeV in 12 differential channels, and Bremsstrahlung X-rays from greater than 5 to greater than 80 KeV in 5 integral channels. In addition, instrumentation to measure ion densities and electric fields were also included on these and, in the case of 31.066, on other near simultaneous payloads. The first flight, 31.066, was launched under pre-magnetic midnight conditions during relatively stable auroral conditions. Flight 31.067 was launched during post-breakup conditions at which time pulsations of approx. 100 seconds duration were evident. The measured radiations including their spectral characteristics are compared for these two events, to appraise their effect on the electrodynamic properties of the middle atmosphere as determined by other rocket-borne measurements.

Goldberg, R. A.↗
NASA NTRS1988

Computational and experimental studies of LEBUs at high device Reynolds numbers

The present paper summarizes computational and experimental studies for large-eddy breakup devices (LEBUs). LEBU optimization (using a computational approach considering compressibility, Reynolds number, and the unsteadiness of the flow) and experiments with LEBUs at high Reynolds numbers in flight are discussed. The measurements include streamwise as well as spanwise distributions of local skin friction. The unsteady flows around the LEBU devices and far downstream are characterized by strain-gage measurements on the devices and hot-wire readings downstream. Computations are made with available time-averaged and quasi-stationary techniques to find suitable device profiles with minimum drag.

Bertelrud, Arild↗
NASA NTRS1988

Cloud field classification based upon high spatial resolution textural features. I - Gray level co-occurrence matrix approach

Stratocumulus, cumulus, and cirrus clouds were identified on the basis of cloud textural features which were derived from a single high-resolution Landsat MSS NIR channel using a stepwise linear discriminant analysis. It is shown that, using this method, it is possible to distinguish high cirrus clouds from low clouds with high accuracy on the basis of spatial brightness patterns. The largest probability of misclassification is associated with confusion between the stratocumulus breakup regions and the fair-weather cumulus.

Welch, R. M.↗
NASA NTRS1989

Fuel spray simulation with two-fluid nozzles

Two-phase interacting flow inside a two-fluid fuel atomizer was investigated and a correction of aerodynamic and liquid-surface forces with characteristic drop diameter was obtained for liquid-jet breakup in Mach 1 gas flow. Nitrogen gas mass-flux was varied from 6 to 50 g/sq cm sec by using four differently sized two-fluid atomizers with nozzle diameters varying from 0.32 to 0.56 cm. The correlation was derived by using the acoustic gas velocity, V sub c, as a basic parameter in defining and evaluating the dimensionless product of the Weber (We) and Reynolds (Re) numbers. By using the definition of WeRe, it was found that the ratio of orifice diameter to Sauter mean drop diameter could be correlated with the dimensionless ratio WeRe and the gas to liquid density ratio.

Ingebo, Robert D.↗
NASA NTRS1989

Time-dependent convection with non-Newtonian viscosity

A numerical model of bottom-heated, two-dimensional convection in boxes of aspect ratios 2.5 and 4.0 was used to study the differences in time-dependent convection between Newtonian and stress-dependent viscosity. The onset of time dependence due to boundary layer instability is found at approximately the same effective Rayleigh number for both rheologies. However, with increasing Rayleigh number, the temporal and spatial fluctuations in the flow field become much more pronounced with non-Newtonian rheology; also, the tendency for breakup of long cells into smaller ones is stronger. The presence of stress-dependent rheology can cause long-wavelength lateral viscosity variations up to an order of magnitude; this result could have strong implications for the interpretation of mantle viscosity from postglacial rebound.

Christensen, Ulrich R.↗
NASA NTRS1989

Investigation of an excited jet diffusion flame at elevated pressure

Experiments are carried out for studying the relationship between flow structure, flow excitation, and the reaction process in the near field of a low-speed coflowing jet diffusion flame. The effect of axial forcing and increasing pressure on the structure and controllability of the flame is studied to elucidate some of the underlying control mechanisms. The experiments are conducted in a variable-pressure flow facility permitting the study of reacting flows in the 10-1000 kPa (0.1-10 atm) pressure range. The flame is excited by a small-amplitude periodic fluctuation added to the central fuel jet exit velocity. Among the varied excitation frequencies employed, a narrow band is found in which several of the flow instabilities seem to be in coincidence, causing periodic breakup of the flame into a series of distinct eddies. This is called the strongly-coupled state. Effects of excitation frequencies at and above the strongly-coupled range are presented.

Strawa, Anthony W.↗
NASA NTRS1989

Nonlinear a Tollmien-Schlichting/vortex interaction in boundary layers

The nonlinear reaction between two oblique three-dimensional Tollmien-Schlichting (TS) waves and their induced streamwise-vortex flow is considered theoretically for an incompressible boundary layer. The same theory applies to the destabilization of an incident vortex motion by subharmonic TS waves, followed by interaction. The scales and flow structure involved are addressed for high Reynolds numbers. The nonlinear interaction is powerful, starting at quite low amplitudes with a triple-deck structure for the TS waves but a large-scale structure for the induced vortex, after which strong nonlinear amplification occurs. This includes nonparallel-flow effects. The nonlinear interaction is governed by a partial differential system for the vortex flow coupled with an ordinary-differential one for the TS pressure. The solution properties found sometimes produce a breakup within a finite distance and sometimes further downstream, depending on the input amplitudes upstream and on the wave angles, and that then leads to the second stages of interaction associated with higher amplitudes, the main second stages giving either long-scale phenomena significantly affected by nonparallelism or shorter quasi-parallel ones governed by the full nonlinear triple-deck response.

Hall, P.↗
NASA NTRS1989

Ultraviolet spectroscopy of pre-main-sequence accretion disks

Low-resolution, ultraviolet spectra of the pre-main-sequence objects Z Canis Majoris, V1057 Cygni, and FU Orionis are presented. Ultraviolet absorption features indicate spectral types of A5 I for FU Ori and F5 I for Z CMa. These results are in reasonable agreement with predictions of simple accretion disk models. The lack of significant veiling of ultraviolet absorption features implies that a hot boundary layer at the inner edge of the disk contributes less than 20 percent of the radiation at 2600-3200 A, which is significantly smaller than expected. It is suggested that accretion has significantly modified the structure of the underlying pre-main-sequence stars in these systems (perhaps by expanding the photosphere or by spinning up a radiative photosphere close to breakup velocity, or both), or that the boundary layer region is much more extended above the disk midplane than standard thin disk theories predict.

Kenyon, S. J.↗
NASA NTRS1989

Gas-phase flowrate effect on disintegrating cryogenic liquid-jets

Two phase liquid and gaseous nitrogen flow in a pneumatic two fluid atomizer was investigated. Characteristic dropsize for cryogenic sprays were measured with a scattered light scanning instrument developed at NASA-Lewis. Tests were conducted primarily in the aerodynamic stripping regime of liquid jet atomization. At a sampling distance of bar-x=1.3 cm, the Sauter mean, D(sub 32), and volume median, D(sub v.5), drop diameters were measured and correlated with nitrogen gas flowrate, W(sub n), to give the following expressions: D sub 32 to the -1=210W(sub n) to the -1.33 and D(sub v.5) to the -1=150 W(sub n to the -1.33, where reciprocal diameters and gas flowrate are in cm (-1) and g/sec, respectively. The exponent 1.33 for nitrogrn gas flowrate, W(sub n), is the same as that predicted by atomization theory for liquid-jet breakup in high velocity gasflow. When the spray was sampled at axial distances of bar-x=2.5 and 4.5 cm downstream of the atomizer, the exponent decreased to 1.2 and 0.9, respectively. This was attributed to the loss of small droplets due to their rapid vaporization.

Ingebo, Robert D.↗
NASA NTRS1990

Effects of turbulence mixing, variable properties, and vaporization on spray droplet combustion

Combustion of liquid fuels in the form of spray droplets is simulated numerically. Various vaporization models are examined as to their performance in finite element calculations involving a turbulent flow field. The Eulerian coordinate for the gas and Lagrangian coordinate for the liquid spray droplets are coupled through source terms being updated in the equations of continuity, momentum, and energy. The k-epsilon and modified eddy breakup models are used for simulating turbulent spray combustion flow field. Numerical results for the droplet trajectories, droplet heating, recirculation characteristics, and effects of evaporation models are evaluated. It is also shown that the finite element method is advantageous in dealing with complex geometries, complex boundary conditions, adaptive unstructured grids.

Kim, Y. M.↗
NASA NTRS1990

Optical characterization of clouds of fine liquid-nitrogen particles

Characteristic drop size, D sub 32, of clouds of fine liquid nitrogen particles was measured with a scattered light scanning instrument developed at NASA-Lewis. Calibration of the instrument was accomplished with suspensions of monosized polystyrene spheres and the scattered light scanner was then used to investigate the mechanism of liquid nitrogen jet disintegration in high velocity gas flow. The Sauter mean diameter, D sub 32, was found to vary inversely with nitrogen gas mass-flux raised to the 1.33 power. Values of D sub 32 varied from 5 to 25 microns and the mass-flux exponent 1.33 agrees well with theory for liquid jet breakup in high velocity gas flow. Loss of fine particles due to the high vaporization rate of liquid nitrogen was avoided by sampling the spray 1.3 cm downstream of the nozzle orifice. The presence of high velocity and thermal gradients in the gas phase also made sampling of the particles quite difficult. As a result, it was necessary to correct the measurements for background noise produced by both highly turbulent gas flow and thermally induced density gradients in the gas phase.

Ingebo, Robert D.↗