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At least 1,495 records · Page 83
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Effect of crossflow velocity on the generation of lift fan jet noise in VTOL aircraft

Analytical studies based on a turbulent mixing noise prediction technique indicate that jet noise power levels are increased when a jet is situated in a crossflow. V/STOL model transport acoustic test data obtained in the NASA Ames 40 ft. x 80 ft. wind tunnel confirmed this jet noise power level increase due to crossflow. Increases up to 6 db at a Strouhal number of 2.5 and crossflow velocity to jet velocity ratio of 0.58 were observed. The power level increases observed in the experimental data confirm the predicted power level increases.

Stimpert, D. L.↗
NASA NTRS1976

Pollutant formation in fuel lean recirculating flows

An opposed reacting jet combustor (ORJ) was tested at a pressure of 1 atmosphere. A premixed propane/air stream was stabilized by a counterflowing jet of the same reactants. The resulting intensely mixed zone of partially reacted combustion products produced stable combustion at equivalence ratios as low as 0.45. Measurements are presented for main stream velocities of 7.74 and 13.6 m/sec with an opposed jet velocity of 96 m/sec, inlet air temperatures from 300 to 600 K, and equivalence ratios from 0.45 to 0.625. Fuel lean premixed combustion was an effective method of achieving low NOx emissions and high combustion efficiencies simultaneously. Under conditions promoting lower flame temperature, NO2 constituted up to 100 percent of the total NOx. At higher temperatures this percentage decreased to a minimum of 50 percent.

Schefer, R. W.↗
NASA NTRS1981

Design and preliminary results of a fuel flexible industrial gas turbine combustor

The design characteristics are presented of a fuel tolerant variable geometry staged air combustor using regenerative/convective cooling. The rich/quench/lean variable geometry combustor is designed to achieve low NO(x) emission from fuels containing fuel bound nitrogen. The physical size of the combustor was calculated for a can-annular combustion system with associated operating conditions for the Allison 570-K engine. Preliminary test results indicate that the concept has the potential to meet emission requirements at maximum continuous power operation. However, airflow sealing and improved fuel/air mixing are necessary to meet Department of Energy program goals.

Novick, A. S.↗
NASA NTRS1986

Iron oxide and hydroxide precipitation from ferrous solutions and its relevance to Martian surface mineralogy

Experiments were performed to examine if the ubiquitousness of a weak magnetic component in all Martian surface fines tested with the Viking Landers can be attributed to ferric iron precipitation in aqueous solution under oxidizing conditions at neutral pH. Ferrous solutions were mixed in deionized water and various minerals were added to separate liquid samples. The iron-bearing additives included hematite, goethite, magnetite, maghemite, lepidocrocite and potassium bromide blank at varying concentrations. IR spectroscopic scans were made to identify any precipitates resulting from bubbling oxygen throughout the solutions; the magnetic properties of the precipitates were also examined. The data indicated that the lepidocrocite may have been preferentially precipitated, then aged to maghemite. The process would account for the presumed thin residue of maghemite on the present Martian surface, long after abundant liquid water on the Martian surface vanished.

Posey-Dowty, J.↗
NASA NTRS1987

Surface flaw reliability analysis of ceramic components with the SCARE finite element postprocessor program

The SCARE (Structural Ceramics Analysis and Reliability Evaluation) computer program on statistical fast fracture reliability analysis with quadratic elements for volume distributed imperfections is enhanced to include the use of linear finite elements and the capability of designing against concurrent surface flaw induced ceramic component failure. The SCARE code is presently coupled as a postprocessor to the MSC/NASTRAN general purpose, finite element analysis program. The improved version now includes the Weibull and Batdorf statistical failure theories for both surface and volume flaw based reliability analysis. The program uses the two-parameter Weibull fracture strength cumulative failure probability distribution model with the principle of independent action for poly-axial stress states, and Batdorf's shear-sensitive as well as shear-insensitive statistical theories. The shear-sensitive surface crack configurations include the Griffith crack and Griffith notch geometries, using the total critical coplanar strain energy release rate criterion to predict mixed-mode fracture. Weibull material parameters based on both surface and volume flaw induced fracture can also be calculated from modulus of rupture bar tests, using the least squares method with known specimen geometry and grouped fracture data. The statistical fast fracture theories for surface flaw induced failure, along with selected input and output formats and options, are summarized. An example problem to demonstrate various features of the program is included.

Gyekenyesi, John P.↗
NASA NTRS1985

Free-jet investigation of mechanically suppressed, high radius ratio coannular plug model nozzles

The experimental and analytical acoustic results of a scale-model investigation or unsuppressed and mechanically suppressed high-radius ratio coannular plug nozzles with inverted velocity and temperature profiles are summarized. Nine coannular nozzle configurations along with a reference conical nozzle were evaluated in the Anechoic Free-Jet Facility for a total of 212 acoustic test points. Most of the tests were conducted at variable cycle engine conditions applicable to advanced high speed aircraft. The tested nozzles included coannular plug nozzles with both convergent and convergent-divergent (C-D) terminations in order to evaluate C-D effectiveness in the reduction of shock-cell noise and 20 and 40 shallow-chute mechanical suppressors in the outer stream in order to evaluate their effectiveness in the reduction of jet noise. In addition to the acoustic tests, mean and turbulent velocity measurements were made on selected plumes of the 20 shallow-chute configuration using a laser velocimeter. At a mixed jet velocity of 700 m/sec, the 20 shallow-chute suppressor configuration yielded peak aft quadrant suppression of 11.5 and 9 PNdB and forward quadrant suppression of 7 and 6 PNdB relative to a baseline conical nozzles during static and simulated flight, respectively. The C-D terminations were observed to reduce shock-cell noise. An engineering spectral prediction method was formulated for mechanically suppressed coannular plug nozzles.

Janardan, B. A.↗
NASA NTRS1987

Surface flaw reliability analysis of ceramic components with the SCARE finite element postprocessor program

The SCARE (Structural Ceramics Analysis and Reliability Evaluation) computer program on statistical fast fracture reliability analysis with quadratic elements for volume distributed imperfections is enhanced to include the use of linear finite elements and the capability of designing against concurrent surface flaw induced ceramic component failure. The SCARE code is presently coupled as a postprocessor to the MSC/NASTRAN general purpose, finite element analysis program. The improved version now includes the Weibull and Batdorf statistical failure theories for both surface and volume flaw based reliability analysis. The program uses the two-parameter Weibull fracture strength cumulative failure probability distribution model with the principle of independent action for poly-axial stress states, and Batdorf's shear-sensitive as well as shear-insensitive statistical theories. The shear-sensitive surface crack configurations include the Griffith crack and Griffith notch geometries, using the total critical coplanar strain energy release rate criterion to predict mixed-mode fracture. Weibull material parameters based on both surface and volume flaw induced fracture can also be calculated from modulus of rupture bar tests, using the least squares method with known specimen geometry and grouped fracture data. The statistical fast fracture theories for surface flaw induced failure, along with selected input and output formats and options, are summarized. An example problem to demonstrate various features of the program is included.

Gyekenyesi, J. P.↗
NASA NTRS1990

Development of a two-dimensional zonally averaged statistical-dynamical model. III - The parameterization of the eddy fluxes of heat and moisture

A number of perpetual January simulations are carried out with a two-dimensional zonally averaged model employing various parameterizations of the eddy fluxes of heat (potential temperature) and moisture. The parameterizations are evaluated by comparing these results with the eddy fluxes calculated in a parallel simulation using a three-dimensional general circulation model with zonally symmetric forcing. The three-dimensional model's performance in turn is evaluated by comparing its results using realistic (nonsymmetric) boundary conditions with observations. Branscome's parameterization of the meridional eddy flux of heat and Leovy's parameterization of the meridional eddy flux of moisture simulate the seasonal and latitudinal variations of these fluxes reasonably well, while somewhat underestimating their magnitudes. New parameterizations of the vertical eddy fluxes are developed that take into account the enhancement of the eddy mixing slope in a growing baroclinic wave due to condensation, and also the effect of eddy fluctuations in relative humidity. The new parameterizations, when tested in the two-dimensional model, simulate the seasonal, latitudinal, and vertical variations of the vertical eddy fluxes quite well, when compared with the three-dimensional model, and only underestimate the magnitude of the fluxes by 10 to 20 percent.

Stone, Peter H.↗
NASA NTRS1950

Foaming of mixtures of pure hydrocarbons

Mixtures of pure liquid hydrocarbons are capable of foaming. Nine hydrocarbons were mixed in pairs, in all possible combinations, and four proportions of each combination. These mixtures were sealed in glass tubes, and the foaming was tested by shaking. Mixtures of aliphatic with other aliphatic hydrocarbons, or of alkyl benzenes with other alkyl benzenes, did not foam. Mixtures of aliphatic hydrocarbons with alkyl benzenes did foam. The proportions of the mixtures greatly affected the foaming, the maximum foaming of 12 of 20 pairs being at the composition 20 percent aliphatic hydrocarbon, 80 percent alkyl benzene. Six seconds was the maximum foam lifetime of any of these mixtures. Aeroshell 120 lubricating oil was fractionated into 52 fractions and a residue by extraction with acetone in a fractionating extractor. The index of refraction, foam lifetime, color, and viscosity of these fractions were measured. Low viscosity and high index fractions were extracted first. The viscosity of the fractions extracted rose and the index decreased as fractionation proceeded. Foam lifetimes and color were lowest in the middle fractions. Significance is attached to the observation that none of the foam lifetimes of the fractions or residue is as high as the foam lifetime of the original Aeroshell, indicating that the foaming is not due to a particular foaming constituent, but rather to the entire mixture.

LUBRICATING OILS - DISTILLATION↗
NASA NTRS1992

Use of AVIRIS data to the definition of optimised specifications for land applications with future spaceborne imaging spectrometers

Recent experience with airborne imaging spectrometers demonstrated the advantages of narrow band sensors over broad band scanners for characterizing the nature, extent, and physical status of typical land surfaces. Information on key spectral features associated with various land surfaces can be obtained from the data of such instruments, which can be used to simulate spaceborne imaging spectrometer data and to assess their information content if comprehensive underpinning is provided by ground data. The collection of such information was an issue of airborne imaging spectrometer campaigns like the NASA MAC-Europe 1991. Airborne and ground data obtained from different test sites in Europe are utilized for a comparative analysis of the spectral signatures of various land surfaces (vegetation, bare soils and rocks, and mixed soil/rock-vegetation) as seen from different imaging spectrometers like Airborne Visible/Infrared Imaging Spectrometer (AVIRIS), GERIS 63 band scanner, and CASI. The following items are discussed: (1) the significance of different spectral regions within the wavelength interval between 0.4 m and 2.5 m for the differentiation of different land units; (2) recommendations on the optimum band selection and band-widths to be used for the application of future satellite-based imaging spectrometers for land applications; (3) the boundaries for the detection of plant features in mixed-soil plant spectra and the influence of different soil properties on the mixture of the spectra; (4) recommendations on the optimum spatial resolution and recording dates for the discrimination of spectral features of various surface types; and (5) evaluation of different data compressing techniques for the optimum extraction of spectral information from imaging spectrometry data.

Bodechtel, J.↗
NASA NTRS1996

Tank Pressure Control Experiment: Thermal Phenomena in Microgravity

The report presents the results of the flight experiment Tank Pressure Control Experiment/Thermal Phenomena (TPCE/TP) performed in the microgravity environment of the space shuttle. TPCE/TP, flown on the Space Transportation System STS-52, was a second flight of the Tank Pressure Control Experiment (TPCE). The experiment used Freon 113 at near saturation conditions. The test tank was filled with liquid to about 83% by volume. The experiment consisted of 21 tests. Each test generally started with a heating phase to increase the tank pressure and to develop temperature stratification in the fluid, followed by a fluid mixing phase for the tank pressure reduction and fluid temperature equilibration. The heating phase provided pool boiling data from large (relative to bubble sizes) heating surfaces (0.1046 m by 0.0742 m) at low heat fluxes (0.23 to 1.16 kW/sq m). The system pressure and the bulk liquid subcooling varied from 39 to 78 kPa and 1 to 3 C, respectively. The boiling process during the entire heating period, as well as the jet-induced mixing process for the first 2 min of the mixing period, was also recorded on video. The unique features of the experimental results are the sustainability of high liquid superheats for long periods and the occurrence of explosive boiling at low heat fluxes (0.86 to 1.1 kW/sq m). For a heat flux of 0.97 kW/sq m, a wall superheat of 17.9 C was attained in 10 min of heating. This superheat was followed by an explosive boiling accompanied by a pressure spike of about 38% of the tank pressure at the inception of boiling. However, at this heat flux the vapor blanketing the heating surface could not be sustained. Steady nucleate boiling continued after the explosive boiling. The jet-induced fluid mixing results were obtained for jet Reynolds numbers of 1900 to 8000 and Weber numbers of 0.2 to 6.5. Analyses of data from the two flight experiments (TPCE and TPCE/TP) and their comparison with the results obtained in drop tower experiments suggest that as Bond number approaches zero the flow pattern produced by an axial jet and the mixing time can be predicted by the Weber number.

Hasan, Mohammad M.↗
NASA NTRS1996

Tank Pressure Control Experiment: Thermal Phenomena in Microgravity. Video 2 of 4

The report presents the results of the flight experiment Tank Pressure Control Experiment/Thermal Phenomena (TPCE/TP) performed in the microgravity environment of the space shuttle. TPCE/TP, flown on the Space Transportation System STS-52, was a second flight of the Tank Pressure Control Experiment (TPCE). The experiment used Freon 113 at near saturation conditions. The test tank was filled with liquid to about 83 percent by volume. The experiment consisted of 21 tests. Each test generally started with a heating phase to increase the tank pressure and to develop temperature stratification in the fluid, followed by a fluid mixing phase for the tank pressure reduction and fluid temperature equilibration. The heating phase provided pool boiling data from large (relative to bubble sizes) heating surfaces (0.1046 m by 0.0742 m) at low heat fluxes (0.23 to 1.16 kW/m(exp 2)). The system pressure and the bulk liquid subcooling varied from 39 to 78 kPa and 1 to 3 deg C, respectively. The boiling process during the entire heating period, as well a jet-induced mixing process for the first 2 min. of the mixing period, was also recorded on video. Analyses of data from the two flight experiments (TPCE and TPCE/TP) and their comparison with the results obtained in drop tower experiments suggest that as Bond number approaches zero the flow pattern produced by an axial jet and the mixing time can be predicted by the Weber number. This is video 2 of 4.

Source record↗
NASA NTRS1996

Tank Pressure Control Experiment: Thermal Phenomena in Microgravity. Video 4 of 4

The report presents the results of the flight experiment Tank Pressure Control Experiment/Thermal Phenomena (TPCE/TP) performed in the microgravity environment of the space shuttle. TPCE/TP, flown on the Space Transportation System STS-52, was a second flight of the Tank Pressure Control Experiment (TPCE). The experiment used Freon 113 at near saturation conditions. The test tank was filled with liquid to about 83 percent by volume. The experiment consisted of 21 tests. Each test generally started with a heating phase to increase the tank pressure and to develop temperature stratification in the fluid, followed by a fluid mixing phase for the tank pressure reduction and fluid temperature equilibration. The heating phase provided pool boiling data from large (relative to bubble sizes) heating surfaces (0.1046 m by 0.0742 m) at low heat fluxes (0.23 to 1.16 kW/m(exp 2)). The system pressure and the bulk liquid subcooling varied from 39 to 78 kPa and 1 to 3 deg C, respectively. The boiling process during the entire heating period, as well a jet-induced mixing process for the first 2 min. of the mixing period, was also recorded on video. Analyses of data from the two flight experiments (TPCE and TPCE/TP) and their comparison with the results obtained in drop tower experiments suggest that as Bond number approaches zero the flow pattern produced by an axial jet and the mixing time can be predicted by the Weber number. This is video 4 of 4.

Source record↗
NASA NTRS1996

Tank Pressure Control Experiment: Thermal Phenomena in Microgravity. Video 1 of 4

The report presents the results of the flight experiment Tank Pressure Control Experiment/Thermal Phenomena (TPCE/TP) performed in the microgravity environment of the space shuttle. TPCE/TP, flown on the Space Transportation System STS-52, was a second flight of the Tank Pressure Control Experiment (TPCE). The experiment used Freon 113 at near saturation conditions. The test tank was filled with liquid to about 83 percent by volume. The experiment consisted of 21 tests. Each test generally started with a heating phase to increase the tank pressure and to develop temperature stratification in the fluid, followed by a fluid mixing phase for the tank pressure reduction and fluid temperature equilibration. The heating phase provided pool boiling data from large (relative to bubble sizes) heating surfaces (0.1046 m by 0.0742 m) at low heat fluxes (0.23 to 1.16 kW/m(exp 2)). The system pressure and the bulk liquid subcooling varied from 39 to 78 kPa and 1 to 3 deg C, respectively. The boiling process during the entire heating period, as well a jet-induced mixing process for the first 2 min. of the mixing period, was also recorded on video. Analyses of data from the two flight experiments (TPCE and TPCE/TP) and their comparison with the results obtained in drop tower experiments suggest that as Bond number approaches zero the flow pattern produced by an axial jet and the mixing time can be predicted by the Weber number. This is video 1 of 4.

Source record↗
NASA NTRS1996

Tank Pressure Control Experiment: Thermal Phenomena in Microgravity. Video 3 of 4

The report presents the results of the flight experiment Tank Pressure Control Experiment/Thermal Phenomena (TPCE/TP) performed in the microgravity environment of the space shuttle. TPCE/TP, flown on the Space Transportation System STS-52, was a second flight of the Tank Pressure Control Experiment (TPCE). The experiment used Freon 113 at near saturation conditions. The test tank was filled with liquid to about 83 percent by volume. The experiment consisted of 21 tests. Each test generally started with a heating phase to increase the tank pressure and to develop temperature stratification in the fluid, followed by a fluid mixing phase for the tank pressure reduction and fluid temperature equilibration. The heating phase provided pool boiling data from large (relative to bubble sizes) heating surfaces (0.1046 m by 0.0742 m) at low heat fluxes (0.23 to 1.16 kW/m(exp 2)). The system pressure and the bulk liquid subcooling varied from 39 to 78 kPa and 1 to 3 deg C, respectively. The boiling process during the entire heating period, as well a jet-induced mixing process for the first 2 min. of the mixing period, was also recorded on video. Analyses of data from the two flight experiments (TPCE and TPCE/TP) and their comparison with the results obtained in drop tower experiments suggest that as Bond number approaches zero the flow pattern produced by an axial jet and the mixing time can be predicted by the Weber number. This is video 3 of 4.

Source record↗
NASA NTRS2001

Experimental Assessment of the Emissions Control Potential of a Rich/Quench/Lean Combustor for High Speed Civil Transport Aircraft Engines

In support of Pratt & Whitney efforts to define the Rich burn/Quick mix/Lean burn (RQL) combustor for the High Speed Civil Transport (HSCT) aircraft engine, UTRC conducted a flametube-scale study of the RQL concept. Extensive combustor testing was performed at the Supersonic Cruise (SSC) condition of a HSCT engine cycle, Data obtained from probe traverses near the exit of the mixing section confirmed that the mixing section was the critical component in controlling combustor emissions. Circular-hole configurations, which produced rapidly-, highly-penetrating jets, were most effective in limiting NOx. The spatial profiles of NOx and CO at the mixer exit were not directly interpretable using a simple flow model based on jet penetration, and a greater understanding of the flow and chemical processes in this section are required to optimize it. Neither the rich-combustor equivalence ratio nor its residence time was a direct contributor to the exit NOx. Based on this study, it was also concluded that (1) While NOx formation in both the mixing section and the lean combustor contribute to the overall emission, the NOx formation in the mixing section dominates. The gas composition exiting the rich combustor can be reasonably represented by the equilibrium composition corresponding to the rich combustor operating condition. Negligible NOx exits the rich combustor. (2) At the SSC condition, the oxidation processes occurring in the mixing section consume 99 percent of the CO exiting the rich combustor. Soot formed in the rich combustor is also highly oxidized, with combustor exit SAE Smoke Number <3. (3) Mixing section configurations which demonstrated enhanced emissions control at SSC also performed better at part-power conditions. Data from mixer exit traverses reflected the expected mixing behavior for off-design jet to crossflow momentum-flux ratios. (4) Low power operating conditions require that the RQL combustor operate as a lean-lean combustor to achieve low CO and high efficiency. (5) A RQL combustor can achieve the emissions goal of EINOX = 5 at the Supersonic Cruise operating condition for a HSCT engine.

Rosfjord, T. J.↗
NASA NTRS2002

On the Formulation of Weakly Singular Displacement/Traction Integral Equations; and Their Solution by the MLPG Method

In this paper, a very simple method is used to derive the weakly singular traction boundary integral equation based on the integral relationships for displacement gradients. The concept of the MLPG method is employed to solve the integral equations, especially those arising in solid mechanics. A moving Least Squares (MLS) interpolation is selected to approximate the trial functions in this paper. Five boundary integral Solution methods are introduced: direct solution method; displacement boundary-value problem; traction boundary-value problem; mixed boundary-value problem; and boundary variational principle. Based on the local weak form of the BIE, four different nodal-based local test functions are selected, leading to four different MLPG methods for each BIE solution method. These methods combine the advantages of the MLPG method and the boundary element method.

Atluri, Satya N.↗
NASA NTRS2001

Experimental Assessment of the Emissions Control Potential of a Rich/Quench/ Lean Combustor for High Speed Civil Transport Aircraft Engines

In support of Pratt & Whitney efforts to define the Rich burn/Quick mix/Lean burn (RQL) combustor for the High Speed Civil Transport (HSCT) aircraft engine, UTRC conducted a flametube-scale study of the RQL concept. Extensive combustor testing was performed at the Supersonic Cruise (SSC) condition of an HSCT engine cycle. Data obtained from probe traverses near the exit of the mixing section confirmed that the mixing section was the critical component in controlling combustor emissions. Circular-hole configurations, which produced rapidly-, highly-penetrating jets, were most effective in limiting NO(x). The spatial profiles of NO(x) and CO at the mixer exit were not directly interpretable using a simple flow model based on jet penetration, and a greater understanding of the flow and chemical processes in this section are required to optimize it. Neither the rich-combustor equivalence ratio nor its residence time was a direct contributor to the exit NO(x). Based on this study, it was also concluded that: (1) While NO(x) formation in both the mixing section and the lean combustor contribute to the overall emission, the NOx formation in the mixing section dominates. The gas composition exiting the rich combustor can be reasonably represented by the equilibrium composition corresponding to the rich combustor operating condition. Negligible NO(x) exits the rich combustor. (2) At the SSC condition, the oxidation processes occurring in the mixing section consume 99 percent of the CO exiting the rich combustor. Soot formed in the rich combustor is also highly oxidized, with combustor exit SAE Smoke Number <3. (3) Mixing section configurations which demonstrated enhanced emissions control at SSC also performed better at part-power conditions. Data from mixer exit traverses reflected the expected mixing behavior for off-design jet to crossflow momentum-flux ratios. (4) Low power operating conditions require that the RQL combustor operate as a lean-lean combustor to achieve low CO and high efficiency. (5) An RQL combustor can achieve the emissions goal of EINO(x) = 5 at the Supersonic Cruise operating condition for an HSCT engine.

Tacina, Robert R.↗