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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Process sensitivity studies of the Westinghouse Sulfur Cycle for hydrogen generation

The effect of variations of acid concentration, pressure, and temperature on the thermal process efficiency of the Westinghouse Sulfur Cycle was examined using the University of Kentucky's HYDRGN program. Modifications to the original program were made to duplicate the process flow sheet and take into account combined-cycle heat-to-work efficiencies for electrochemical work requirements, aqueous solutions, and heat-of-mixing effects. A total of 125 process variations were considered (acid concentration: 50-90 w/o; pressure: 15-750 psia; temperature: 922-1366 K (2000 F)). The methods of analysis, results, and conclusions are presented.

Carty, R.↗
NASA NTRS1978

Blade row dynamic digital compression program. Volume 2: J85 circumferential distortion redistribution model, effect of Stator characteristics, and stage characteristics sensitivity study

The results of dynamic digital blade row compressor model studies of a J85-13 engine are reported. The initial portion of the study was concerned with the calculation of the circumferential redistribution effects in the blade-free volumes forward and aft of the compression component. Although blade-free redistribution effects were estimated, no significant improvement over the parallel-compressor type solution in the prediction of total-pressure inlet distortion stability limit was obtained for the J85-13 engine. Further analysis was directed to identifying the rotor dynamic response to spatial circumferential distortions. Inclusion of the rotor dynamic response led to a considerable gain in the ability of the model to match the test data. The impact of variable stator loss on the prediction of the stability limit was evaluated. An assessment of measurement error on the derivation of the stage characteristics and predicted stability limit of the compressor was also performed.

Tesch, W. A.↗
NASA NTRS1980

An acoustic sensitivity study of general aviation propellers

This paper describes the results of a study in which a systematic approach has been taken in studying the effect of selected propeller parameters on the character and magnitude of propeller noise. Four general aviation aircraft were chosen, i.e., a Cessna 172, Cessna 210, Cessna 441, and a 19 passenger commuter concept, to provide a range in flight velocity, engine horsepower, and gross weight. The propeller parameters selected for examination consisted of number of blades, rpm reduction, thickness/chord reduction, activity factor reduction, proplets, airfoil improvement, sweep, position of maximum blade loading, and diameter reduction.

Korkan, K. D.↗
NASA NTRS1982

Low-thrust Isp sensitivity study

A comparison of the cooling requirements and attainable specific impulse performance of engines in the 445 to 4448N thrust class utilizing LOX/RP-1, LOX/Hydrogen and LOX/Methane propellants is presented. The unique design requirements for the regenerative cooling of low-thrust engines operating at high pressures (up to 6894 kPa) were explored analytically by comparing single cooling with the fuel and the oxidizer, and dual cooling with both the fuel and the oxidizer. The effects of coolant channel geometry, chamber length, and contraction ratio on the ability to provide proper cooling were evaluated, as was the resulting specific impulse. The results show that larger contraction ratios and smaller channels are highly desirable for certain propellant combinations.

Schoenman, L.↗
NASA NTRS1984

A global low order spectral model designed for climate sensitivity studies

A two level, global, spectral model using pressure as a vertical coordinate is developed. The system of equations describing the model is nonlinear and quasi-geostrophic. A moisture budget is calculated in the lower layer only with moist convective adjustment between the two layers. The mechanical forcing of topography is introduced as a lower boundary vertical velocity. Solar forcing is specified assuming a daily mean zenith angle. On land and sea ice surfaces a steady state thermal energy equation is solved to calculate the surface temperature. Over the oceans the sea surface temperatures are prescribed from the climatological average of January. The model is integrated to simulate the January climate.

Hanna, A. F.↗
NASA NTRS1988

Technology sensitivity studies for a Mach 3.0 civil transport

The level of technological sophistication required for the economic viability and environmental acceptability of a Mach 3.0-cruise SST is evaluated, with a view to the development schedule and initial operating date into which the maturity of various essential technologies will translate. Attention is given to the effect of advanced aerodynamic, propulsion, structural and subsystem technologies on takeoff gross weight. A dramatic impact is noted to result from the combination of prospective technological advances in flow laminarization, advanced structures and materials, etc.

Coen, Peter G.↗
NASA NTRS1988

Influence of land surface roughness on atmospheric circulation and precipitation - A sensitivity study with a general circulation model

The influence of land surface roughness on the large scale atmospheric circulation and rainfall is examined by comparing three sets of simulations made with a general circulation model in which the land surface roughness length, z(0), was reduced from 45 cm to 0.02 cm. It is found that the reduced surface roughness produced a two-fold increase in the boundary layer wind speed, a two-fold decrease in the magnitude of the surface stress, and almost no change in the surface evaporation and surface sensible heat flux. It is suggested that the height of the earth's vegetation cover has a large influence on the boundary layer water vapor transport convergence and the rainfall distribution.

Sud, Y. C.↗
NASA NTRS1989

Sensitivity study of advection and diffusion coefficients in a two-dimensional stratospheric model using excess carbon 14 data

The time evolution of excess C-14 in the stratosphere and the troposphere from October 1963 to December 1966 is investigated using the Caltech/JPL two-dimensioanal transport model, with transport coefficients taken from Yang and Tung (1989). It is found that the model successfully accounts for observations reported previously. It is calculated that excess C-14 is removed from the atmosphere with surface deposition velocities of 0.003 cm/sec in the Southern Hemisphere and 0.005 cm/sec in the Northern Hemisphere. This result is contrary to the current understanding that the oceans are the dominant sink for excess C-14.

Shia, Run-Lie↗
NASA NTRS1992

Preconditioning for stratospheric sudden warmings - Sensitivity studies with a numerical model

The phenomenon of preconditioning for sudden stratospheric warming events is investigated using a 3D primitive equation model adapted from the model used by Rose and Brasseur (1989). In order to identify the conditions that make the flow preconditioned, the model was initialized alternately with observed and with artificially constructed 'hybrid' stratospheric flow patterns. Two observed warmings were investigated, February 1979 and February 1989. The artificially constructed hybrid flow fields used upper-level winds (above 10 mb) from one period and lower-level winds (below 10 mb) from another. The results of model simulations indicate that the flow in the lower and middle stratosphere is capable of serving as a predictor of the potential for a major sudden warming, with the occurrence of a warming depending only on the lower-level winds.

Smith, Anne K.↗
NASA NTRS1992

Preconditioning for stratospheric sudden warmings - Sensitivity studies with a numerical model

Results are presented of numerical experiments performed to determine what constitutes preconditioning for stratospheric sudden warmings. A number of 20-d runs were performed with a 3D primitive equation model. Runs varied in that they had different (zonally symmetric) initial fields and different lower boundary planetary wave fields, both based on NMC data for particular days. Initial and boundary data were used from the two minor and the sole major sudden warmings of January-February 1979 and some minor and the sole major sudden warmings of January-February 1989. To isolate the properties of the initial conditions from preconditioned cases and those with no warming, hybrid initial fields were created by combining data from two different days, one preconditioned and the other not. Runs with the hybrid initial conditions indicate that it is the lower stratospheric winds that are important in characterizing a preconditioned flow. It is suggested that it would be possible for a preconditioned state to exist for at least a short time without a warming occurring.

Smith, Anne K.↗
NASA NTRS1997

Model Evaluation and Sensitivity Studies for Determining Aircraft Effects on the Global Atmosphere

This project, started in July 1995 and ending in July 1996, related: to evaluation of the possible importance of soot and sulfur dioxide emissions from subsonic and supersonic aircraft; to research contributions and special responsibilities for NASA AEAP assessments of subsonic aircraft and High Speed Civil Transport aircraft; and to science team responsibilities supporting the development of the three-dimensional atmospheric chemistry model of the Global Modeling Initiative.

Wuebbles, Donald J.↗
NASA NTRS1993

Climate Sensitivity Studies of the Greenland Ice Sheet Using Satellite AVHRR, SMMR, SSM/I and in Situ Data

The feasibility of using satellite data for climate research over the Greenland ice sheet is discussed. In particular, we demonstrate the usefulness of Advanced Very High Resolution Radiometer (AVHRR) Local Area Coverage (LAC) and Global Area Coverage (GAC) data for narrow-band albedo retrieval. Our study supports the use of lower resolution AVHRR (GAC) data for process studies over most of the Greenland ice sheet. Based on LAC data time series analysis, we can resolve relative albedo changes on the order of 2-5%. In addition, we examine Scanning Multichannel Microwave Radiometer (SMMR) and Special Sensor Microwave Imager (SSM/I) passive microwave data for snow typing and other signals of climatological significance. Based on relationships between in situ measurements and horizontally polarized 19 and 37 GHz observations, wet snow regions are identified. The wet snow regions increase in aerial percentage from 9% of the total ice surface in June to a maximum of 26% in August 1990. Furthermore, the relationship between brightness temperatures and accumulation rates in the northeastern part of Greenland is described. We found a consistent increase in accumulation rate for the northeastern part of the ice sheet from 1981 to 1986.

Steffen, K.↗
NASA NTRS1998

Two Dimensional Wake Vortex Simulations in the Atmosphere: Preliminary Sensitivity Studies

A numerical large-eddy simulation model is currently being used to quantify aircraft wake vortex behavior with meteorological observables. The model, having a meteorological framework, permits the interaction of wake vortices with environments characterized by crosswind shear, stratification, and humidity. The addition of grid-scale turbulence as an initial condition appeared to have little consequence. Results show that conventional nondimensionalizations work very well for vortex pairs embedded in stably stratified flows. However, this result is based on simple environments with constant Brunt-Vaisala frequency. Results presented here also show that crosswind profiles exert important and complex interactions on the trajectories of wake vortices. Nonlinear crosswind profiles tended to arrest the descent of wake vortex pairs. The member of the vortex pair with vorticity of same sign as the vertical change in the ambient along-track vorticity may be deflected upwards.

Proctor, F. H.↗
NASA NTRS2007

Sensitivity Study for Sensor Optical and Electric Crosstalk Based on Spectral Measurements: An Application to Developmental Sensors Using Heritage Sensors Such As MODIS

The process of developing new sensors for space flight frequently builds upon the designs and experience of existing heritage space flight sensors. Frequently in the development and testing of new sensors, problems are encountered that pose the risk of serious impact on successful retrieval of geophysical products. This paper describes an approach to assess the importance of optical and electronic cross-talk on retrieval of geophysical products using new MODIS-like sensors through the use of MODIS data sets. These approaches may be extended to any sensor characteristic and any sensor where that characteristic may impact the Level 1 products so long as validated geophysical products are being developed from the heritage sensor. In this study, a set of electronic and/or optical cross-talk coefficients are postulated. These coefficients are sender-receiver influence coefficients and represent a sensor signal contamination on any detector on a focal plane when another band's detectors on that focal plane are stimulated with a monochromatic light. The approach involves using the postulated cross-talk coefficients on an actual set of MODIS data granules. The original MODIS data granules and the cross-talk impacted granules are used with validated geophysical algorithms to create the derived products. Comparison of the products produced with the original and cross-talk impacted granules indicates potential problems, if any, with the characteristics of the developmental sensor that are being studied.

Butler, James J.↗