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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 289 records · Page 16

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NASA NTRS1978

Ion convection and the formation of the mid-latitude F region ionization trough

Total ion concentration and ion drift velocity data from Atmospheric Explorer C are used to examine the convective flow of plasma in the vicinity of the midlatitude F region ionization trough. It is found that the low-latitude portion of the premidnight trough is a region of slow eastward plasma drift while the poleward portion is characterized by generally westward flow. The reversal from eastward to westward flow is described. It is proposed that the plasma flux tubes within the premidnight trough have corotated eastward into the evening local time sector from dusk before stagnating and flowing westward at higher latitudes in the nighttime sector. The role of F region recombination in trough formation is considered.

Spiro, R. W.↗

NASA NTRS1979

Release adiabat measurements on minerals: The effect of viscosity

The current inversion of pressure-particle velocity data for release from a high pressure shock state to a pressure-density path is analyzed. It is assumed that the release process is isentropic. It was shown that for geological materials below stresses of 150 GPa, the effective viscosity must be 1000 kg/m/s in order that the viscous (irreversible) work carried out on the material in the shock state remains small compared to the mechanical work recovered upon adiabatic rarefaction. The available data pertaining to the offset of the Rayleigh line from the Hugoniot for minerals, the magnitude of the shear stress in the high pressure shock state for minerals, and the direct measurements of the viscosities of several engineering materials shocked to pressures below 150 GPa yield effective viscosities of 1000 kg/m/s or less. An inferance that this indicates that the conditions for isentropic release of minerals from shock states are achieved, and a conclusion that the application of the Riemann integral to obtain pressure-density states along the release adiabats of minerals in shock experiments is valid are made.

Jeanloz, R.↗

NASA NTRS1979

Particle size and velocity measurement in flames by laser anemometer

Simultaneous droplet size and velocity measurements by a particle counting Laser Doppler Anemometer (LDA) in kerosene fuel sprays under burning and non-burning conditions are presented. Particle sizes are derived from pulse height analysis of the mean LDA signals and velocities are simultaneously determined by measuring Doppler shift frequencies. The measurements show that droplet velocity is a function of droplet diameter for burning and non-burning conditions, and spatially averaged size distributions are derived from velocity data. A comparison of results obtained under burning and non-burning conditions show changes in size distribution due to preferential vaporization of small droplets, acceleration due to thermal expansion of gases, and corresponding changes in droplet momentum.

Chigier, N. A.↗

NASA NTRS1979

Release adiabat measurements on minerals - The effect of viscosity

The paper examines the effect of viscosity in the release adiabat measurements on minerals. The current inversion of pressure-particle velocity data for release from a high-pressure shock state to a pressure-density path usually depends critically upon the assumption that the release process is isentropic. It has been shown that the effective viscosity for geological materials below stresses of 150 GPa must be at least 1000 kg/m/s so that viscous work in the shock state remains small compared to mechanical work recovered upon adiabatic rarefaction. The magnitude of the shear stress in the shock state in minerals and viscosities of engineering materials shocked to pressures below 150 GPa show effective viscosities of about 1000 kg/m/s or less indicating that the conditions for isentropic release of materials from shock states are achieved and that the Riemann integral can be applied to obtain pressure-density states along the release adiabats of minerals.

Jeanloz, R.↗

NASA NTRS1980

Turbulent eddy diffusivity and mean eddy lifetimes measured in spray combustion

A quantitative description of the eddy structure that occurs in turbulent combustion processes can be obtained by the use of laser velocimetry, as shown in this work. The mean eddy length scales, eddy lifetimes, and turbulent diffusivity have been determined in a spray combustion flame for the first time. Velocity data was obtained at various locations within the flame, and standard correlation techniques were modified and then applied to reduce the data. In order to assess how the spray burns, the measured eddy lifetimes were compared with the relevant reaction times and drop lifetimes. Conditions that are conducive to group combustion of the droplets, rather than individual droplet combustion, were found to exist in the upstream region of the spray. Local measurements of the hydrocarbon concentration also support the conclusion that the majority of droplets undergo group combustion. However, the data indicate that some of the larger drops can survive the initial burning region and form a dilute spray downstream where conditions favor individual droplet combustion.

Driscoll, J. F.↗

NASA NTRS1981

Basic research in wake vortex alleviation using a variable twist wing

The variable twist wing concept was used to investigate the relative effects of lift and turbulence distribution on the rolled up vortex wake. Several methods of reducing the vortex strength behind an aircraft were identified. These involve the redistribution of lift spanwise on the wing and drag distribution along the wing. Initial attempts to use the variable twist wing velocity data to validate the WAKE computer code have shown a strong correlation, although the vorticity levels were not exactly matched.

Morris, D. J.↗

NASA NTRS1981

Laser-velocimeter flow-field measurements of an advanced turboprop

Non-intrusive measurements of velocity about a spinner-propeller-nacelle configuration at a Mach number of 0.8 were performed. A laser velocimeter, specifically developed for these measurements in the NASA Lewis 8-foot by 6-foot Supersonic Wind Tunnel, was used to measure the flow-field of the advanced swept SR-3 turboprop. The laser velocimeter uses an argon ion laser and a 2-color optics system to allow simultaneous measurements of 2-components of velocity. The axisymmetric nature of the propeller-nacelle flow-field permits two separate 2 dimensonal measurements to be combined into 3 dimensional velocity data. Presented are data ahead of and behind the prop blades and also a limited set in between the blades. Aspects of the observed flow-field such as the tip vortex are discussed.

Serafini, J. S.↗

NASA NTRS1981

Laser-velocimeter flow-field measurements of an advanced turboprop

Non-intrusive measurements of velocity about a spinner-propeller-nacelle configuration at a Mach number of 0.8 have been performed. A laser velocimeter, specifically developed for these measurements in the NASA Lewis 8- by 6-foot Supersonic Wind Tunnel, was used to measure the flow-field of the advanced swept SR-3 propeller. The laser velocimeter uses an argon ion laser and a 2-color optics system to allow simultaneous measurements of 2-components of velocity. The axisymmetric nature of the propeller-nacelle flow-field permits two separate 2-dimensional measurements to be combined into 3-dimensional velocity data. Presented are data ahead of and behind the propeller blades and also a limited set in between the blades. Aspects of the observed flow-field such as the tip vortex are discussed.

Serafini, J. S.↗

NASA NTRS1982

Study of VTOL in ground-effect flow field including temperature effect

Detailed pressure, temperature, and velocity data were obtained for twin-fan configurations in-ground-effect and flow models to aid in predicting pressures and upwash forces on aircraft surfaces were developed. For the basic experiments, 49.5 mm-diameter jets were used, oriented normal to a simulated round plane, with pressurized, heated air providing a jet. The experimental data consisted of: (1) the effect of jet height and temperature on the ground, model, and upwash pressures, and temperatures, (2) the effect of simulated aircraft surfaces on the isolated flow field, (3) the jet-induced forces on a three-dimensional body with various strakes, (4) the effects of non-uniform coannular jets. For the uniform circular jets, temperature was varied from room temperature (24 C) to 232 C. Jet total pressure was varied between 9,300 Pascals and 31,500 Pascals. For the coannular jets, intended to represent turbofan engines, fan temperature was maintained at room temperature while core temperature was varied from room temperature to 437 C. Results are presented.

Hill, W. G.↗

NASA NTRS1981

A four dimensional variational analysis experiment

A demonstration that the four dimensional variational analysis method using the governing equations as exact constraints can be successfully employed for a perfect model and for a simple, but nonlinear, system is presented. The method is stable in an assimilation cycle. The method reconstructs the unobservable variables; in the case demonstrated, no velocity data was observed. The analysis errors are much smaller than the observing system errors.

Hoffman, R.↗

NASA NTRS1982

Analysis of vibration induced error in turbulence velocity measurements from an aircraft wing tip boom

The effect of rolling motion of a wing on the magnitude of error induced due to the wing vibration when measuring atmospheric turbulence with a wind probe mounted on the wing tip was investigated. The wing considered had characteristics similar to that of a B-57 Cambera aircraft, and Von Karman's cross spectrum function was used to estimate the cross-correlation of atmospheric turbulence. Although the error calculated was found to be less than that calculated when only elastic bendings and vertical motions of the wing are considered, it is still relatively large in the frequency's range close to the natural frequencies of the wing. Therefore, it is concluded that accelerometers mounted on the wing tip are needed to correct for this error, or the atmospheric velocity data must be appropriately filtered.

Akkari, S. H.↗

NASA NTRS1982

Space Shuttle Orbiter descent navigation

The entry operational sequence (OPS 3) begins approximately 2 hours prior to the deorbit maneuver and continues through atmospheric entry, terminal area energy management (TAEM), approach and landing, and rollout. During this flight phase, the navigation state vector is estimated by the Space Shuttle Orbiter onboard navigation system. This estimate is computed using a six-element sequential Kalman filter, which blends inertial measurement unit (IMU) delta-velocity data with external navaid data. The external navaids available to the filter are tactical air navigation (TACAN), barometric altimeter, and microwave scan beam landing system (MSBLS). Attention is given to the functional design of the Orbiter navigation system, the descent navigation sensors and measurement processing, predicted Kalman gains, correlation coefficients, and current flights navigation performance.

Montez, M. N.↗

NASA NTRS1981

Dependence of sea-surface microwave emissivity on friction velocity as derived from SMMR/SASS

The sea-surface microwave emissivity is derived using SMMR brightness temperatures and SASS inferred friction velocities for three North Pacific Seasat passes. The results show the emissivity increasing linearly with friction velocity with no obvious break between the foam-free and foam regimes up to a friction velocity of about 70 cm/sec (15 m/sec wind speed). For horizontal polarization the sensitivity of emissivity to friction velocity greatly increases with frequency, while for vertical polarization the sensitivity is much less and is independent of frequency. This behavior is consistent with two-scale scattering theory. A limited amount of high friction velocity data above 70 cm/sec suggests an additional increase in emissivity due to whitecapping.

Wentz, F. J.↗

NASA NTRS1983

Optical and X-ray observations of 2S 0921-630

The present investigation is concerned with photometric and spectroscopic measurements of 2S 0921-630 covering the years 1975-82. The X-ray source 2S 0921-630 was discovered by Li et al. (1978) and identified with an approximately 17th magnitude star showing He II 4686 A and H-beta in emission. Attention is given to photoelectric photometry, photographic photometry, aspects of periodic behavior, spectroscopy, radial velocity measurements and equivalent widths, and X-ray observations. It is found that the radial velocity data confirm the 9-day period previously suggested for the system and exclude alternative periods of 17.9 and 7.7 days.

Branduardi-Raymont, G.↗

NASA NTRS1984

Interference drag in a simulated wing-fuselage juncture

The interference drag in a wing fuselage juncture as simulated by a flat plate and a body of constant thickness having a 1.5:1 elliptical leading edge is evaluated experimentally. The experimental measurements consist of mean velocity data taken with a hot wire at a streamwise location corresponding to 16 body widths downstream of the body leading edge. From these data, the interference drag is determined by calculating the total momentum deficit (momentum area) in the juncture and also in the two dimensional turbulent boundary layers on the flat plate and body at locations sufficiently far from the juncture flow effect. The interference drag caused by the juncture drag as measured at this particular streamwise station is -3% of the total drag due to the flat plate and body boundary layers in isolation. If the body is considered to be a wing having a chord and span equal to 16 body widths, the interference drag due to the juncture is only -1% of the frictional drag of one surface of such a wing.

Kubendran, L. R.↗

NASA NTRS1984

Theoretical and experimental studies in support of the geophysical fluid flow experiment

Computer programming was completed for digital acquisition of temperature and velocity data generated by the Geophysical Fluid Flow Cell (GFFC) during the upcoming Spacelab 3 mission. A set of scenarios was developed which covers basic electro-hydrodynamic instability, highly supercritical convection with isothermal boundaries, convection with imposed thermal forcing, and some stably stratified runs to look at large-scale thermohaline ocean circulations. The extent to which the GFFC experimental results apply to more complicated circumstances within the Sun or giant planets was assessed.

Hart, J.↗

NASA NTRS1983

Detection of solar gravity mode oscillations

An analysis of solar velocity data obtained at the Stanford Solar Observatory shows the existence of solar global oscillations in the range 45 to 105 microHz (160 to 370 minutes). These oscillations are interpreted as internal gravity modes of degree l = 1 and l = 2. A good estimate of the order of the modes has also been made. Previously announced in STAR as N84-11086

Delache, P.↗

NASA NTRS1984

Detection of solar gravity mode oscillations

The detection of g-mode oscillations in solar-velocity data obtained at Stanford Solar Observatory during 1977-1980 is reported, summarizing the results of Scherrer and Wilcox (1983) and Delache and Scherrer (1983). Spectra are shown, and the analysis results are presented in a table and graph. A total of 14 peaks are identified in the frequency range 45-105 microhertz, of which seven are assigned to a series with l = 1 and n = 6-10 and four are assigned to a series with l = 2 and n = 15-20; a peak at 59.52 microhertz can be identified as either l = 1, n = 10 or as l = 2, n = 17.

Scherrer, P. H.↗