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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Flow visualization study of delta wings in wing-rock motion

Water tunnel flow visualizations have been conducted for the wing-rock phenomenon in the cases of models having different leading-edge sweeps and roundness. Wing rock, which is noted to occur in the absence of asymmetric vortex liftoff, vortex breakdown, and static hysteresis, is seen to be initiated by flowfield asymmetries that are induced by flow disturbances and vortex interactions near the apex region; one vortex is thereby strengthened while the other is weakened, inducing a roll moment. Leading-edge roundness decreases vortex strength and reduces vortex spacing, reducing the tendency to wind rock and coupled vortex motions at higher angles-of-attack.

Ng, T. Terry↗
NASA NTRS1989

Development of non-conventional control methods for high angle of attack flight using vortex manipulation

Low-speed wind tunnel experiments have been conducted to define methods for the manipulation of a generic fighter forebody's vortices in order to generate controlled yawing moments at high alpha. Attention is given to two vortex-control schemes: one involving independently controlled forebody tip strakes, and the other individually controlled blowing ports on the forebody. The most effective methods for forebody yawing-moment control were found to be the minimization of natural asymmetry with a pair of symmetrically mounted tip strakes, and the perturbation of the vortex system away from the symmetric condition with asymmetric blowing.

Malcolm, Gerald N.↗
NASA NTRS1989

The roles of dynamical and chemical processes in determining the stratospheric concentration of ozone in one-dimensional and two-dimensional models

The two-dimensional model of Ko et al. (1985) was used to calculate the stratospheric concentrations of ozone, to determine the principal modes of balance for different stratospheric regions. The results of this analysis show that the local concentration of ozone in different regions of stratosphere is determined by balances between different mechanisms. In the upper stratosphere, the ozone concentration is dominated by photochemical processes, whereas in the mid-lower stratosphere, the bulk of ozone appears to be controlled by an interaction between the transport and the photochemical processes. The results point to the limitations of one-dimensional models, which fail to properly account for the effect of transport in the lower stratosphere.

Ko, Malcolm K. W.↗
NASA NTRS1989

US/UK Advanced Short Takeoff and Vertical Landing program (ASTOVL)

Both the U.S. and the UK have substantial technology bases from past and current R and D programs, a common background of service experience and, potentially, much common interest in the future use of advanced STOVL combat aircraft. Equally interested in the operational advantages of the short takeoff and vertical landing capability of combat aircraft, combined with supersonic and high agility performance, the U.S. and the UK have agreed to collaborate on ASTOVL research underwritten by a Memorandum of Understanding (MOU) (1986) between the two governments. The paper describes the aims and provisions of the MOU, gives the results of studies, illustrates the technology development underway, and outlines the future ASTOVL technology program. Particular attention is given to concept studies on advanced vectored thrust, the ejector augmentor, the hybrid tandem fan, and the remote augmented lift system.

Levine, J.↗
NASA NTRS1989

Report of the 1988 2-D Intercomparison Workshop, chapter 3

Several factors contribute to the errors encountered. With the exception of the line-by-line model, all of the models employ simplifying assumptions that place fundamental limits on their accuracy and range of validity. For example, all 2-D modeling groups use the diffusivity factor approximation. This approximation produces little error in tropospheric H2O and CO2 cooling rates, but can produce significant errors in CO2 and O3 cooling rates at the stratopause. All models suffer from fundamental uncertainties in shapes and strengths of spectral lines. Thermal flux algorithms being used in 2-D tracer tranport models produce cooling rates that differ by as much as 40 percent for the same input model atmosphere. Disagreements of this magnitude are important since the thermal cooling rates must be subtracted from the almost-equal solar heating rates to derive the net radiative heating rates and the 2-D model diabatic circulation. For much of the annual cycle, the net radiative heating rates are comparable in magnitude to the cooling rate differences described. Many of the models underestimate the cooling rates in the middle and lower stratosphere. The consequences of these errors for the net heating rates and the diabatic circulation will depend on their meridional structure, which was not tested here. Other models underestimate the cooling near 1 mbar. Suchs errors pose potential problems for future interactive ozone assessment studies, since they could produce artificially-high temperatures and increased O3 destruction at these levels. These concerns suggest that a great deal of work is needed to improve the performance of thermal cooling rate algorithms used in the 2-D tracer transport models.

Jackman, Charles H.↗
NASA NTRS1989

Measurement of damping of graphite epoxy composite materials and structural joints

The damping capacity of graphite epoxy materials and structural joints was evaluated. The damping ratio of different composite specimens and bonded joints were systematically evaluated under normal atmospheric conditions and in a vacuum environment. Free and forced vibration test methods were employed for measuring the damping ratios. The effect of edge support conditions on the damping value of a composite tube specimen was studied by using a series of experiments performed on the specimen with different edge supports. It was found that simulating a free-free boundary conditions by having no constraints at the ends gives the lowest value of the material damping of the composite. The accuracy of the estimation of the damping ratio value was improved by using a curve-fitting technique on the response data obtained through measurement. The effect of outgassing (moisture desorption) on the damping capacity was determined by measuring the damping ratio of the tube specimen in a vacuum environment before and after outgassing had occurred. The effects of high and low temperatures on the damping was also investigated by using a series of experiments on tube and beam specimens. An analytical model to study the vibrations of a bonded lap joint system was formulated. Numerical results were generated for different overlap ratios of the system. These were compared with experimental results. In order to determine the influence of bonded joints on the material damping capacity, experiments were conducted on bonded lap-jointed and double-butt-jointed specimens. These experimental results were compared with simple beam specimens with no joints.

Crocker, Malcolm J.↗
NASA NTRS1989

Adapting to variable prismatic displacement

In each of two studies, subjects were exposed to a continuously changing prismatic displacement with a mean value of 19 prism diopters (variable displacement) and to a fixed 19-diopter displacement (fixed displacement). In Experiment 1, significant adaptation (post-pre shifts in hand-eye coordination) was found for fixed, but not for variable, displacement. Experiment 2 demonstrated that adaptation was obtained for variable displacement, but it was very fragile and is lost if the measures of adaptation are preceded by even a very brief exposure of the hand to normal or near-normal vision. Contrary to the results of some previous studies, an increase in within-S dispersion was not found of target pointing responses as a result of exposure to variable displacement.

Welch, Robert B.↗
NASA NTRS1989

Optical, gravitational, and kinesthetic determinants of judged eye level

Subjects judged eye level, defined in three distinct ways relative to three distinct reference planes: a gravitational horizontal, giving the gravitationally referenced eye level (GREL); a visible surface, giving the surface-referenced eye level (SREL); and a plane fixed with respect to the head, giving the head-referenced eye level (HREL). The information available for these judgements was varied by having the subjects view an illuminated target that could be placed in a box which: (1) was pitched at various angles, (2) was illuminated or kept in darkness, (3) was moved to different positions along the subject's head-to-foot body axis, and (4) was viewed with the subjects upright or reclining. The results showed: (1) judgements of GREL made in the dark were 2.5 deg lower than in the light, with a significantly greater variability; (2) judged GREL was shifted approximately half of the way toward SREL when these two eye levels did not coincide; (3) judged SREL was shifted about 12 percent of the way toward HREL when these two eye levels did not coincide, (4) judged HREL was shifted about half way toward SREL when these two eye level did not coincide and when the subject was upright (when the subject was reclining, HREL was shifted approx. 90 percent toward SREL); (5) the variability of the judged HREL in the dark was nearly twice as great with the subject reclining than with the subject upright. These results indicate that gravity is an important source of information for judgement of eye level. In the absence of information concerning the direction of gravity, the ability to judge HREL is extremely poor. A visible environment does not seem to afford precise information as to judgements of direction, but it probably does afford significant information as to the stability of these judgements.

Stoper, Arnold E.↗
NASA NTRS1990

Development of non-conventional control methods for high angle of attack flight using vortex manipulation

Methods of manipulating the forebody vortices on a generic fighter model to produce controlled yawing moments at high angles of attack were investigated. Forces and moments were measured on the complete configuration and on the isolated forebody. Two schemes for vortex control on the forebody were evaluated: individually-controlled tip strakes and individually-controlled blowing ports. The effectiveness of the forebody strakes in controlling forebody side forces was strongly dependent on the size and location of the strakes. A yawing moment can be produced by deploying the forebody strakes asymmetrically, or can be eliminated by deploying the strakes symmetrically. The most effective strake position was found to be near the primary separation point, between 105 and 120 deg from windward. Blowing on the surface of the model was also shown to have a strong effect on the yawing moment. Blowing either forward or aft tangential to the surface appears to be more effective than blowing normal to the surface. The most effective method to control the yawing moment on the forebody was to minimize the natural asymmetry with a pair of small symmetrically mounted tip strakes and to perturb the vortex system away from the symmetric condition with asymmetric blowing.

Malcolm, Gerald N.↗
NASA NTRS1989

Intensive parameters of enstatite chondrite metamorphism

A geothermometer based on the assemblage kamacite-quartz-enstatite-oldhamite-troilite found in enstatite chondrites is described. Data obtained with the geothermometer reveal that the EL6 meteorites experienced temperatures exceeding 1000 C. These temperatures imply a metal-sulfide melting event that may have fractionated the melt from the source region.

Fogel, Robert A.↗
NASA NTRS1989

Hubble Space Telescope - New view of an ancient universe

Scheduled for a March 1990 Shuttle launch, the Hubble Space Telescope (HST) will give astronomers a tool of unprecedented accuracy to observe the universe: an optically superb instrument free of the atmospheric turbulence, distortion, and brightness that plague all earthbound telescopes. The observatory will carry into orbit two cameras, a pair of spectrographs, a photometer, and fine guidance sensors optimized for astrometry. The diffraction limit for the 2.4-m aperture of the HST corresponds to 90 percent of the radiation from a point source falling within a circle of 0.1 arcsec angular radius at a wavelength of 633 nm. The 15-year mission will make observations in the ultraviolet as well as the optical spectral region, thus, widening the wavelength window to a range extending from the Lyman alpha wavelengnth of 122 nm to just about 2 microns. The observational program that awaits the HST will include the study of planetary atmospheres, in particular the search for aerosols; the study of globular star clusters within the Galaxy; and the determination of the present rate of expansion of the universe. The HST will achieve resolutions of 0.1 arcsec consistently, regardless of observation duration. The HST engineering challenge is also discussed.

Leckrone, David S.↗
NASA NTRS1989

Artificial gravity for long duration spaceflight

This paper reviews the fundamental physical properties of gravitational and centrifugal forces, describes the physiological changes that result from long-term exposure to the nearly gravity-free environment of space, and explores the nature of these changes. The paper then cites currently employed and advanced techniques that can be used to prevent some of these changes. Following this review, the paper examines the potential use of artificial gravity as the ultimate technique to maintain terrestrial levels of physiological functioning in space, and indicates some of the critical studies that must be conducted and some of the trade-offs that must be made before artificial gravity can intelligently be used for long duration spaceflight.

Cohen, Malcolm M.↗
NASA NTRS1990

The role of chlorine chemistry in Antarctic ozone loss - Implications of new kinetic data

New kinetic data yielding a slower formation rate and larger absorption cross sections of Cl2O2 are incorporated into a photochemical model to reassess the role of chlorine chemistry in accounting for the ozone reductions derived from TOMS observations in different regions of the Antarctic polar vortex during 1987. The model is further constrained by existing measurements from the Airborne Antarctic Ozone Experiment and the National Ozone Expedition II. Calculated concentrations of ClO based on the new kinetic data increase by almost a factor of two between the collar and core regions of the vortex during the second half of September. The calculated ozone reductions in the vortex core appear to be consistent with the TOMS observations in spite of the slower rate for the self-reaction of ClO.

Rodriguez, Jose M.↗
NASA NTRS1990

Model calculations of the relative effects of CFCs and their replacements on stratospheric ozone

Because chlorine has been linked to the destruction of stratospheric ozone, the use of many fully halogenated compounds, such as the chlorofluorocarbons CFC-11 and -12, is restricted by international agreement. Hydrohalocarbons are under intensive development as replacements for CFCs. Because they contain hydrogen, these gases are susceptible to tropospheric destruction which significantly shortens their atmospheric lifetimes,. Model calculations show that chlorine-containing hydrohalocarbons have less effect on ozone, by an order of magnitude, than their regulated counterparts.

Fisher, Donald A.↗
NASA NTRS1990

Response of an interactive two-dimensional model to ozone changes - An estimate of the radiative dynamical feedback effect

The response of the interactive two-dimensional stratospheric model described by Schneider et al. (1989) to an increased chemical removal of ozone and the sensitivity of the calculated assessments to the choice of eddy diffusion coefficients are investigated using a simplified ozone chemistry model. It was found that the radiative dynamical feedback in the model leads to ozone losses at high altitudes to be about one third smaller than predicted by a model with fixed temperature and circulation. The radiative feedback has a smaller effect on ozone (losses decrease by about one sixth) in the lower stratosphere. Predicted ozone losses increase with decreasing dissipation and eddy diffusion in the lower stratosphere.

Schneider, Hans R.↗
NASA NTRS1990

Conjugate echoes of artificially injected electron beams detected optically by means of new image processing

Artificial auroral streaks were detected following two upward injections of energetic electrons (38 keV and 26 keV) from the Echo 4 rocket-borne electron accelerator. Newly developed image processing techniques are used to detect and describe the streaks. It is found that the potential of the payload remained below 1 kV during 45 mA injections at an altitude of 210 km. The echo streaks show little dispersion in time or space, suggesting that the portion of the beam returning to the northern hemisphere loss cone remained collimated and nearly monoenergetic. There was, however, a 70 percent loss in the return flux. The causes of this loss are discussed.

Hallinan, Thomas J.↗
NASA NTRS1990

Atmospheric trace gases and global climate - A seasonal model study

Atmospheric models with seasonal cycles are used to study the possible near-future changes in latitudinal and vertical distributions of atmospheric ozone and temperature caused by increases of trace gases. It is found that increases of CFCs, CH4, and N2O may add to the surface warming from increased CO2. Calculations based on projected trends of CO2, N2O, CH4, and CFCs show that the annual mean and global mean surface temperature could warm by as much as 2.5 C by the year 2050, with larger warming at high latitudes. The results suggest that the warming in the lower stratosphere and upper troposphere is much larger than that at the surface, especially during the summer season.

Wang, Wei-Chyung↗