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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 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Atmospheric methane measurement instrument using a Zeeman-split He-Ne laser

The construction of an atmospheric methane measurement instrument based on a Zeeman-split IR He-Ne laser is reported. The laser has a tranverse magnetic field over about 2/3 of its gain length and can oscillate at an (unsplit) frequency (2947.91/cm) centered on a methane absorption line, or on either of two frequencies split by + or - 0.055/cm from the center, with low CH4 absorption. The laser is tuned to dwell sequentially at each frequency, giving two differential absorption measurements in each 46-ms tuning cycle. Atmospheric measurements are made using two multiple pass absorption cells, one with fast (0.75-s) and one with slow (5-s) flow response times. Fluctuations in ambient CH4 of about 20-ppb (rms, 1-s averaging) are detected, with interference fringe effects the dominant noise source. The instrument has operated in a field experiment (NASA GTE/ABLE-3A) in Alaska.

Mcmanus, J. Barry↗
NASA NTRS1989

Grids for DSMC computation of two and three-dimensional flows

Contemporary grid schemes for use in Direct Simulation Monte Carlo (DSMC) method of computing two- and three-dimensional flows are briefly surveyed. The grids described include: (1) simple, constant area cells defined by a rectangular grid; (2) multilevel rectangular grids; (3) adaptive rectangular cells; (4) 'point reference' scheme; (5) body-fitted 'analytical' cells; (6) 'general' schemes; (7) 'general' schemes with subcells; (8) orthogonal transformation to rectangular grid; (9) structural tetrahedral grids; (10) rectangular multilevel subcells with adaptive body-fitted cells.

Bird, G. A.↗
NASA NTRS1990

Disintegration of liquid sheets

The development, stability, and disintegration of liquid sheets issuing from a two-dimensional air-assisted nozzle is studied. Detailed measurements of mean drop size and velocity are made using a phase Doppler particle analyzer. Without air flow the liquid sheet converges toward the axis as a result of surface tension forces. With airflow a quasi-two-dimensional expanding spray is formed. The air flow causes small variations in sheet thickness to develop into major disturbances with the result that disruption starts before the formation of the main break-up region. In the two-dimensional variable geometry air-blast atomizer, it is shown that the air flow is responsible for the formation of large, ordered, and small chaotic 'cell' structures.

Mansour, Adel↗
NASA NTRS1990

The Spacelab J mission

This paper describes Spacelab J (SL-J), its mission characteristics, features, parameters and configuration, the unique nature of the shared reimbursable cooperative effort with the National Space Development Agency (NASDA) of Japan and the evolution, content and objectives of the mission scientific experiment complement. The mission is planned for launch in 1991. This long module mission has 35 experiments from Japan as well as 9 investigations from the United States. The SL-J payload consists of two broad scientific disciplines which require the extended microgravity or cosmic ray environment: (1) materials science such as crystal growth, solidification processes, drop dynamics, free surface flows, gas dynamics, metallurgy and semiconductor technology; and (2) life science including cell development, human physiology, radiation-induced mutations, vestibular studies, embryo development, and medical technology. Through an international agreement with NASDA, NASA is preparing to fly the first Japanese manned, scientific, cooperative endeavor with the United States.

Cremin, J. W.↗
NASA NTRS1992

Cartesian based grid generation/adaptive mesh refinement

Grid adaptation has recently received attention in the computational fluid dynamics (CFD) community as a means to capture the salient features of a flowfield by either moving grid points of a structured or by adding cells in an unstructured manner. An approach based on a background cartesian mesh is investigated from which the geometry is 'cut' out of the mesh. Once the mesh is obtained, a solution on this coarse grid is found, that indicates which cells need to be refined. This process of refining/solving continues until the flow is grid refined in terms of a user specified global parameter (such as drag coefficient etc.). The advantages of this approach are twofold: the generation of the base grid is independent of the topology of the bodies or surfaces around/through which the flow is to be computed, and the resulting grid (in uncut regions) is highly isotropic, so that the truncation error is low. The flow solver (which, along with the grid generation is still under development) uses a completely unstructured data base, and is a finite volume, upwinding scheme. Current and future work will address generating Navier-Stokes suitable grids by using locally aligned and normal face/cell refining. The attached plot shows a simple grid about two turbine blades.

Coirier, William J.↗
NASA NTRS1991

Circulation of the gyres of the world ocean: Observation modeling using TOPEX/Poseidon altimeter data

The overall objectives of the proposed investigation are to study the dynamics of the large-scale recirculating cells of water in the ocean, which are loosely defined as 'gyres' in this study. A gyre is normally composed of a swift western boundary current (e.g., the Gulf Stream and the Kuroshio), a tight recirculating cell attached to the current, and a large-scale sluggish return flow. The water, of course, is not entirely recirculating within a gyre. The exchange of water among gyres is an important process in maintaining the meridional heat transport of the ocean. The gyres constitute a major mode of water movement in the ocean and play significant roles in the global climate system.

Fu, Lee-Lueng↗
NASA NTRS1995

Stokes problems for moving half-planes

New exact solutions of the Navier-Stokes equations are obtained for the unbounded and bounded oscillatory and impulsive tangential edgewise motion of touching half-infinite plates in their own plane. In contrast to Stokes classical solutions for the harmonic and impulsive motion of an infinite plane wall, where the solutions are separable or have a simple similarity form, the present solutions have a two-dimensional structure in the near region of the contact between the half-infinite plates. Nevertheless, it is possible to obtain relatively simple closed-form solutions for the flow field in each case by defining new variables which greatly simplify the r- and theta- dependence of the solutions in the vicinity of the contact region. These solutions for flow in a half-infinite space are then extended to bounded flows in a channel using an image superposition technique. The impulsive motion has application to the motion near geophysical faults, whereas the oscillatory motion has arisen in the design of a novel oscillating half-plate flow chamber for examining the effect of fluid shear stress on cultured cell monolayers.

NASA Discipline Musculoskeletal↗
NASA NTRS1986

Model system for studies of microbial dynamics at exuding surfaces such as the rhizosphere

An autoclavable all-glass system for studying microbial dynamics at permeable surfaces is described. Standard hydrophobic or hydrophilic membranes (46-mm diameter) of various pore sizes were supported on a glass frit through which nutrient solutions were pumped by a peristaltic pump. The pump provided a precisely controlled flow at speeds of 0.5 to 500 ml of defined or natural cell exudates per h, which passed through the membrane into a receiving vessel. The construction allowed a choice of membranes, which could be modified. The system was tested with a bacterium, isolated from rape plant roots (Brassica napus L.), that was inoculated on a hydrophilic membrane filter and allowed to develop into a biofilm. A defined medium with a composition resembling that of natural rape root exudate was pumped through the membrane at 0.5 ml/h. Scanning electron microscopic examinations indicated that the inoculum formed microcolonies embedded in exopolymers evenly distributed over the membrane surface. The lipid composition and content of poly-beta-hydroxybutyrate in free-living and adhered cells were determined by gas chromatography. The bacterial consumption of amino acids in the exudate was also studied.

NASA Discipline Number 61-10↗
NASA NTRS2004

Conical Magnetic Bearings Developed for Active Stall Control in Gas Turbine Engines

Active stall control is a current research area at the NASA Glenn Research Center that offers a great benefit in specific fuel consumption by allowing the gas turbine to operate beyond the onset of stall. Magnetic bearings are being investigated as a new method to perform active stall control. This enabling global aviation safety technology would result in improved fuel efficiency and decreased carbon dioxide emissions, as well as improve safety and reliability by eliminating oil-related delays and failures of engine components, which account for 40 percent of the commercial aircraft departure delays. Active stall control works by perturbing the flow in front of the compressor stage such that it cancels the pressure wave, which causes the compressor to go into stall. Radial magnetic bearings are able to whirl the shaft so that variations in blade tip leakage would flow upstream causing a perturbation wave that could cancel the rotating stall cell. Axial or thrust magnetic bearings cannot be used to cancel the surge mode in the compressor because they have a very low bandwidth and thus cannot modulate at a high enough frequency. Frequency response is limited because the thrust runner cannot be laminated. To improve the bandwidth of magnetic thrust bearings, researchers must use laminations to suppress the eddy currents. A conical magnetic bearing can be laminated, resulting in increased bandwidth in the axial direction. In addition, this design can produce both radial and thrust force in a single bearing, simplifying the installation. The proposed solution combines the radial and thrust bearing into one design that can be laminated--a conical magnetic bearing. The new conical magnetic bearing test rig, funded by a Glenn fiscal year 2002 Director's Discretionary Fund, was needed because none of the existing rigs has an axial degree of freedom. The rotor bearing configuration will simulate that of the main shaft on a gas turbine engine. One conical magnetic bearing replaces the ball bearing in front of the compressor, and the second replaces the roller bearing behind the burner. The rig was made operational to 10,000 rpm under Smart Efficient Components funding, and both position and current adaptive vibration control have been demonstrated. Upon program completion, recommendations will be made as to the efficacy of the conical magnetic bearing for active stall control.

Trudell, Jeffrey J.↗
NASA NTRS2005

Electroporation System for Sterilizing Water

A prototype of an electroporation system for sterilizing wastewater or drinking water has been developed. In electroporation, applied electric fields cause transient and/or permanent changes in the porosities of living cells. Electroporation at lower field strengths can be exploited to increase the efficiency of chemical disinfection (as in chlorination). Electroporation at higher field strengths is capable of inactivating and even killing bacteria and other pathogens, without use of chemicals. Hence, electroporation is at least a partial alternative to chlorination. The transient changes that occur in micro-organisms at lower electric-field strengths include significantly increased uptake of ions and molecules. Such increased uptake makes it possible to achieve disinfection at lower doses of chemicals (e.g., chlorine or ozone) than would otherwise be needed. Lower doses translate to lower costs and reduced concentrations of such carcinogenic chemical byproducts as trichloromethane. Higher electric fields cause cell membranes to lose semipermeability and thereby become unable to function as selective osmotic barriers between the cells and the environment. This loss of function is the cause of the cell death at higher electric-field intensities. Experimental evidence does not indicate cell lysis but, rather, combined leaking of cell proteins out of the cells as well as invasion of foreign chemical compounds into the cells. The concept of electroporation is not new: it has been applied in molecular biology and genetic engineering for decades. However, the laboratory-scale electroporators used heretofore have been built around small (400-microliter) cuvettes, partly because the smallness facilitates the generation of electric fields of sufficient magnitude to cause electroporation. Moreover, most laboratory- scale electroporators have been designed for testing static water. In contrast, the treatment cell in the present system is much larger and features a flow-through geometry, such that electric fields strong enough to effect 99.9- percent disinfection can be applied to water flowing in a pipe.

Schlager, Kenneth J.↗
NASA NTRS1986

Convection pattern morphology and variations (invited review)

A fairly straightforward consideration of the interaction between a southward interplanetary magnetic field and the Earth's magnetic field will result in the prediction of a two cell convection pattern in the high latitude ionosphere. This is shown schematically where the antisunward flow at high latitudes results from the application of the solar wind electric field to the ionosphere and the return sunward flow results from an electric field generated in the plasma sheet to ensure continuity. This convection pattern can be quite easily characterized in terms of the radius of the approximately circular region containing the antisunward flow, called the polar cap and the maximum potential difference applied across this region. The convection pattern described is at least understandable in terms of solar wind/magnetosphere interaction in which open field lines are recirculated in the polar cap and a viscous interaction process exists near the flanks of the magnetosphere's equatorial plane giving rise to the lower latitude convection cells.

Heelis, R. A.↗
NASA NTRS1997

Study of Injection of Helium into Supersonic Air Flow Using Rayleigh Scattering

A study of the transverse injection of helium into a Mach 3 crossflow is presented. Filtered Rayleigh scattering is used to measure penetration and helium mole fraction in the mixing region. The method is based on planar molecular Rayleigh scattering using an injection-seeded, frequency-doubled ND:YAG pulsed laser and a cooled CCD camera. The scattered light is filtered with an iodine absorption cell to suppress stray laser light. Preliminary data are presented for helium mole fraction and penetration. Flow visualization images obtained with a shadowgraph and wall static pressure data in the vicinity of the injection are also presented.

Seaholtz, Richard G.↗
NASA NTRS2003

Convective Array Cooling for a Solar Powered Aircraft

A general characteristic of photovoltaics is that they increase in efficiency as their operating temperature decreases. Based on this principal, the ability to increase a solar aircraft's performance by cooling the solar cells was examined. The solar cells were cooled by channeling some air underneath the cells and providing a convective cooling path to the back side of the array. A full energy balance and flow analysis of the air within the cooling passage was performed. The analysis was first performed on a preliminary level to estimate the benefits of the cooling passage. This analysis established a clear benefit to the cooling passage. Based on these results a more detailed analysis was performed. From this cell temperatures were calculated and array output power throughout a day period were determined with and without the cooling passage. The results showed that if the flow through the cooling passage remained laminar then the benefit in increased output power more than offset the drag induced by the cooling passage.

Colozza, Anthony J.↗
NASA NTRS1980

High efficiency wraparound contact solar cells /HEWACS/

A cell technology, producing high efficiency wrap-around contact solar cells (HEWACS), with both electrical contacts on the back and AMO conversion efficiencies of almost 15%, is presented. A flow chart indicating the baseline process sequence along with the process changes is given. Tests checking for coating delamination and contact integrity, those measuring contact strength, and thermal cycle tests, successfully demonstrated that this cell technology is ready to be moved to the pilot production stage.

Gillanders, M.↗
NASA NTRS1995

Numerical modeling of spray combustion with an advanced VOF method

This paper summarizes the technical development and validation of a multiphase computational fluid dynamics (CFD) numerical method using the volume-of-fluid (VOF) model and a Lagrangian tracking model which can be employed to analyze general multiphase flow problems with free surface mechanism. The gas-liquid interface mass, momentum and energy conservation relationships are modeled by continuum surface mechanisms. A new solution method is developed such that the present VOF model can be applied for all-speed flow regimes. The objectives of the present study are to develop and verify the fractional volume-of-fluid cell partitioning approach into a predictor-corrector algorithm and to demonstrate the effectiveness of the present approach by simulating benchmark problems including laminar impinging jets, shear coaxial jet atomization and shear coaxial spray combustion flows.

Chen, Yen-Sen↗
NASA NTRS2014

Toward Automatic Verification of Goal-Oriented Flow Simulations

We demonstrate the power of adaptive mesh refinement with adjoint-based error estimates in verification of simulations governed by the steady Euler equations. The flow equations are discretized using a finite volume scheme on a Cartesian mesh with cut cells at the wall boundaries. The discretization error in selected simulation outputs is estimated using the method of adjoint-weighted residuals. Practical aspects of the implementation are emphasized, particularly in the formulation of the refinement criterion and the mesh adaptation strategy. Following a thorough code verification example, we demonstrate simulation verification of two- and three-dimensional problems. These involve an airfoil performance database, a pressure signature of a body in supersonic flow and a launch abort with strong jet interactions. The results show reliable estimates and automatic control of discretization error in all simulations at an affordable computational cost. Moreover, the approach remains effective even when theoretical assumptions, e.g., steady-state and solution smoothness, are relaxed.

Simulations↗
NASA NTRS1992

Efficiency of an AMTEC recirculating test cell, experiments and projections

The alkali metal thermal to electric converter (AMTEC) is an electrochemical device for the direct conversion of heat to electrical energy with efficiencies potentially near Carnot. The future usefulness of AMTEC for space power conversion depends on the efficiency of the devices. Systems studies have projected from 15 to 35 percent thermal to electric conversion efficiencies, and one experiment has demonstrated 19 percent efficiency for a short period of time. Recent experiments in a recirculating test cell (RTC) have demonstrated sustained conversion efficiencies as high as 10.2 percent early in cell life and 9.7 percent after maturity. Extensive thermal and electrochemical analysis of the cell during several experiments demonstrated that the efficiency could be improved in two ways. First, the electrode performance could be improved. The electrode for these tests operated at about one third the power density of state of the art electrodes. The low power density was caused by a combination of high series resistance and high mass flow resistance. Reducing these resistances could improve the efficiency to greater than 10 percent. Second, the cell thermal performance could be improved. Efficiencies greater than 14 percent could be realized through reducing the radiative thermal loss. Further improvements to the efficiency range predicted by systems studies can be accomplished through the development and use of an advanced condenser with improved reflectivity, close to that of a smooth sodium film, and the series connecting of individual cells to further reduce thermal losses.

Underwood, M. L.↗