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NASA NTRS1986

Large scale structure in universes dominated by cold dark matter

The theory of Gaussian random density field peaks is applied to a numerical study of the large-scale structure developing from adiabatic fluctuations in models of biased galaxy formation in universes with Omega = 1, h = 0.5 dominated by cold dark matter (CDM). The angular anisotropy of the cross-correlation function demonstrates that the far-field regions of cluster-scale peaks are asymmetric, as recent observations indicate. These regions will generate pancakes or filaments upon collapse. One-dimensional singularities in the large-scale bulk flow should arise in these CDM models, appearing as pancakes in position space. They are too rare to explain the CfA bubble walls, but pancakes that are just turning around now are sufficiently abundant and would appear to be thin walls normal to the line of sight in redshift space. Large scale streaming velocities are significantly smaller than recent observations indicate. To explain the reported 700 km/s coherent motions, mass must be significantly more clustered than galaxies with a biasing factor of less than 0.4 and a nonlinear redshift at cluster scales greater than one for both massive neutrino and cold models.

Bond, J. Richard↗

NASA NTRS1987

Adherent Al2O3 scales formed on undoped NiCrAl alloys

Changes in the spalling behavior of Al2O3 scales formed on an undoped NiCrAl alloy are described. Two samples of Ni-15Cr-13Al (wt pct), one a control and the other sanded, were subjected to 25 oxidation cycles. It is observed that adherent scales formed on the sanded sample; however, the control sample had speckled, spalled scales. The data reveal that the adherent scales are caused by repeated removal of surface layers after each oxidation cycle. It is determined that interfacial segregation of sulfur influences spallation and sulfur removal increases bonding. The effect of moisture on scale adhesions is investigated.

Smialek, James L.↗

NASA NTRS1986

Effects of eddy initial conditions on nonlinear forcing of planetary scale waves by amplifying baroclinic eddies

The previous study of Young and Villere concerning growth of planetary scale waves forced by wave-wave interactions of amplifying intermediate scale baroclinic eddies is extended to investigate effects of different eddy initial conditions. A global, spectral, primitive equation model is used for the calculations. For every set of eddy initial conditions considered, growth rates of planetary modes are considerably greater than growth rates computed from linear instability theory for a fixed zonally independent basic state. However, values of growth rates ranged over a factor of 3 depending on the particular set of eddy initial conditions used. Nonlinear forcing of planetary modes via wave-wave coupling becomes more important than baroclinic growth on the basic state at small values of the intermediate-scale modal amplitudes. The relative importance of direct transfer of kinetic energy from intermediate scales of motion to a planetary mode, compared to baroclinic conversion of available potential energy to kinetic energy within that planetary mode, depends on the individual case. In all cases, however, the transfer of either kinetic or available potential energy to the planetary modes was accomplished principally by wave-wave transfer from intermediate scale eddies, rather than from the zonally averaged state. The zonal wavenumber 2 planetary mode was prominent in all solutions, even in those for which eddy initial conditions were such that a different planetary mode was selectively forced at the start. General characteristics of the structural evolution of the planetary wave components of total heat and momentum flux, and modal structures themselves, were relatively insensitive to variations in eddy initial conditions, even though quantitative details varied from case to case.

Young, Richard E.↗

NASA NTRS1987

Observations of large-scale Birkeland currents with Viking

Data from the Viking Magnetic Field Experiment and Hot Plasma Experiment acquired on March 25, 1986 are analyzed. The large-scale region 1 and region 2 Birkeland current systems (with densities of about 0.1 microA/sq m) were readily identified in the morning sector at altitudes of 12,500 to 13,000 km. Embedded in the large-scale region 1 system are small-scale intense currents that are not necessarily aligned in the east-west geomagnetic direction. The major carriers of the large-scale region 1 Birkeland currents appear to be upward-flowing electrons with energies below 10 eV. Embedded within this flux can be spatially limited regions of 'hotter' electron fluxes that carry small-scale currents. The correlation of magnetic and particle observations obtained here supports previous suggestions that the region 1 currents in the morning sector have their source in the boundary layer and that the region 2 currents are associated with the plasma sheet.

Potemra, T. A.↗

NASA NTRS1987

Effects of scale on supersonic combustor performance

A series of tests has been carried out to investigate the effects of various scale parameters on the direct connect scramjet combustor performance. The calculated combustion efficiency appears to be independent of scale for the same geometry, but tests with more precise scaling of the entire combustor are required to verify this. Combustion, however, can be strongly dependent on geometry for the same scale. It is suggested that the beneficial aspects of certain geometric or scale variations can be combined to improve the overall performance.

Diskin, Glenn S.↗

NASA NTRS1987

Estimation of local spatial scale

The concept of local scale asserts that for a given class of psychophysical measurements, performance at any two visual field locations is equated by magnifying the targets by the local scale associated with each location. Local scale has been hypothesized to be equal to cortical magnification or alternatively to the linear density of receptors or ganglion cells. Here, it is shown that it is possible to estimate local scale without prior knowledge about the scale or its physiological basis.

Watson, Andrew B.↗

NASA NTRS1987

Formation of large-scale structure from cosmic-string loops and cold dark matter

Some results from a numerical simulation of the formation of large-scale structure from cosmic-string loops are presented. It is found that even though G x mu is required to be lower than 2 x 10 to the -6th (where mu is the mass per unit length of the string) to give a low enough autocorrelation amplitude, there is excessive power on smaller scales, so that galaxies would be more dense than observed. The large-scale structure does not include a filamentary or connected appearance and shares with more conventional models based on Gaussian perturbations the lack of cluster-cluster correlation at the mean cluster separation scale as well as excessively small bulk velocities at these scales.

Melott, Adrian L.↗

NASA NTRS1987

Rossby waves and two-dimensional turbulence in a large-scale zonal jet

Homogeneous barotropic beta-plane turbulence is investigated, taking into account the effects of spatial inhomogeneity in the form of a zonal shear flows. Attention is given to the case of zonal flows that are barotropically stable and of larger scale than the resulting transient eddy field. Numerical simulations reveal that large-scale zonal flows alter the picture of classical beta-plane turbulence. It is found that the disturbance field penetrates to the largest scales of motion, that the larger disturbance scales show a tendency to meridional rather than zonal anisotropy, and that the initial spectral transfer rate away from an isotropic intermediate-scale source is enhanced by the shear-induced transfer associated with straining by the zonal flow.

Shepherd, Theodor G.↗

NASA NTRS1988

Use of Dynamically Scaled Models for Studies of the High-Angle-of-Attack Behavior of Airplanes

Dynamically scaled, free-flying models are used by the National Aeronautics and Space Administration (NASA) to study the stalling and spinning characteristics of civil and military airplane configurations. Such tests have been conducted for many different designs, and it has been possible to correlate the results predicted by the model tests with flight test results obtained in the investigations. The present paper describes four of the dynamic model testing techniques used at the NASA Langley Research Center, including the scaling laws used in the construction of models and in the interpretation of results. Predictions of stall/spin behavior based on model results have generally been very accurate, and the model tests are regarded as an invaluable precursor to full-scale flight tests. However, aerodynamic scale effects between some models and full-scale airplanes due to differences in test values of Reynolds number have resulted in erroneous predictions for a few configurations. A discussion of these effects is provided, together with the approach used to modify the model so that its behavior more closely matches that of the airplane. Finally, two typical applications of the techniques to the X-29A research airplane and several general aviation research airplanes are presented to illustrate the type of information provided by the tests.

Joseph R Chambers↗

NASA NTRS1988

Use of dynamically scaled models for studies of the high-angle-of-attack behavior of airplanes

Joseph R Chambers↗

NASA NTRS1989

Predicting minimum Al concentrations for protective scale fromation on Ni-base alloys. I - Isothermal oxidation. II - Cyclic oxidation

Criteria proposed to predict the minimum bulk Al concentration for the formation of protective Al2O3 scales on Ni-based alloys during isothermal oxidation (two criteria proposed by Wagner, 1952 and 1959) and cyclic oxidation (the criteria proposed by Wahl, 1983, and Whittle, 1972/Wahl, 1983) were applied to Ni-Al and Ni-Cr-Al(Zr) alloys, respectively. It is shown that the first Wagner (1952) criterion underpredicted, by a factor of 3, the experimentally observed minimum Al concentration for the formation of an external Al2O3 scale on Ni-Al alloys at 1200 C; the second Wagner criterion predicted a transition from internal oxidation to continuous Al2O3 formation in good agreement with experimentally observed concentrations. It was also found that the two criteria for an Al2O3 scale formation during cyclic oxidation of Ni-Cr-Al(Zr) alloys were inadequate to predict the minimum Al concentration necessary for repeated formation of an Al2O3 scale, regardless of the adherence of the scale.

Nesbitt, James A.↗

NASA NTRS1990

On estimating scale invariance in stratocumulus cloud fields

Examination of cloud radiance fields derived from satellite observations sometimes indicates the existence of a range of scales over which the statistics of the field are scale invariant. Many methods were developed to quantify this scaling behavior in geophysics. The usefulness of such techniques depends both on the physics of the process being robust over a wide range of scales and on the availability of high resolution, low noise observations over these scales. These techniques (area perimeter relation, distribution of areas, estimation of the capacity, d0, through box counting, correlation exponent) are applied to the high resolution satellite data taken during the FIRE experiment and provides initial estimates of the quality of data required by analyzing simple sets. The results of the observed fields are contrasted with those of images of objects with known characteristics (e.g., dimension) where the details of the constructed image simulate current observational limits. Throughout when cloud elements and cloud boundaries are mentioned; it should be clearly understood that by this structures in the radiance field are meant: all the boundaries considered are defined by simple threshold arguments.

Seze, Genevieve↗

NASA NTRS1990

Experimental studies of 90 deg corner cascades in the National Full-Scale Aerodynamic Complex

Two 90 deg, fixed geometry, turning vane cascades were replaced in the 40- by 80-foot wind tunnel circuit of the National Full-Scale Aerodynamic Complex as a part of a major facility upgrade. Prior to the replacement of these vanes, small-scale, two-dimensional tests were conducted to assess the aerodynamic performance of the original, 1930's technology vane geometry and a new vane geometry which was developed using a modern cascade design code. The small scale tests were conducted in the 1/10th-Scale Cascade Test Facility and included measurements of total pressure, static pressure, and flow angularity distributions in the wake of the cascade and static pressure distributions along the vane profiles. Test results and a detailed comparison of the two vanes designs are presented. Based on these results, the new design was chosen and subsequently installed in the wind tunnel. During the integrated systems test of the upgraded facility, two of the 52 vanes in the first cascade were instrumented near midspan. The full-scale test results are presented, these show the cascade pressure loss coefficient to be slightly larger than obtained in the small-scale tests. Elements of the three-dimensional flow field upstream of the cascade, which effect can impact cascade performance, are discussed and recommendations for future research are given.

Meyn, Larry A.↗

NASA NTRS1990

Strength Scaling in Fiber Composites

A research program was initiated to study and isolate the factors responsible for scale effects in the tensile strength of graphite/epoxy composite laminates. Four layups were chosen with appropriate stacking sequences so as to highlight individual and interacting failure modes. Four scale sizes were selected for investigation including full scale size, 3/4, 2/4, and 1/4, with n = to 4, 3, 2, and 1, respectively. The full scale specimen sizes was 32 piles thick as compared to 24, 16, and 8 piles for the 3/4, 2/4, and 1/4 specimen sizes respectively. Results were obtained in the form of tensile strength, stress-strain curves and damage development. Problems associated with strength degradation with increasing specimen sizes are isolated and discussed. Inconsistencies associated with strain measurements were also identified. Enhanced x ray radiography was employed for damage evaluation, following step loading. It was shown that fiber dominated layups were less sensitive to scaling effects compared to the matrix dominated layups.

Kellas, Sotiris↗

NASA NTRS1990

A scaling law of radial gas distribution in disk galaxies

Based on the idea that local conditions within a galactic disk largely determine the region's evolution time scale, researchers built a theoretical model to take into account molecular cloud and star formations in the disk evolution process. Despite some variations that may be caused by spiral arms and central bulge masses, they found that many late-type galaxies show consistency with the model in their radial atomic and molecular gas profiles. In particular, researchers propose that a scaling law be used to generalize the gas distribution characteristics. This scaling law may be useful in helping to understand the observed gas contents in many galaxies. Their model assumes an exponential mass distribution with disk radius. Most of the mass are in atomic gas state at the beginning of the evolution. Molecular clouds form through a modified Schmidt Law which takes into account gravitational instabilities in a possible three-phase structure of diffuse interstellar medium (McKee and Ostriker, 1977; Balbus and Cowie, 1985); whereas star formation proceeds presumably unaffected by the environmental conditions outside of molecular clouds (Young, 1987). In such a model both atomic and molecular gas profiles in a typical galactic disk (as a result of the evolution) can be fitted simultaneously by adjusting the efficiency constants. Galaxies of different sizes and masses, on the other hand, can be compared with the model by simply scaling their characteristic length scales and shifting their radial ranges to match the assumed disk total mass profile sigma tot(r).

Wang, Zhong↗

NASA NTRS1990

Effects of large-scale wind driven turbulence on sound propagation

Acoustic measurements made in the atmosphere have shown significant fluctuations in amplitude and phase resulting from the interaction with time varying meteorological conditions. The observed variations appear to have short term and long term (1 to 5 minutes) variations at least in the phase of the acoustic signal. One possible way to account for this long term variation is the use of a large scale wind driven turbulence model. From a Fourier analysis of the phase variations, the outer scales for the large scale turbulence is 200 meters and greater, which corresponds to turbulence in the energy-containing subrange. The large scale turbulence is assumed to be elongated longitudinal vortex pairs roughly aligned with the mean wind. Due to the size of the vortex pair compared to the scale of the present experiment, the effect of the vortex pair on the acoustic field can be modeled as the sound speed of the atmosphere varying with time. The model provides results with the same trends and variations in phase observed experimentally.

Noble, John M.↗

NASA NTRS1991

Strength scaling in fiber composites

A research program was initiated to study and isolate the factors responsible for scale effects in the tensile strength of graphite/epoxy composite laminates. Four layups were chosen with appropriate stacking sequences so as to highlight individual and interacting failure modes. Four scale sizes were selected for investigation including full scale size, 3/4, 2/4, and 1/4, with n = to 4, 3, 2, and 1, respectively. The full scale specimen sizes was 32 piles thick as compared to 24, 16, and 8 piles for the 3/4, 2/4, and 1/4 specimen sizes respectively. Results were obtained in the form of tensile strength, stress-strain curves and damage development. Problems associated with strength degradation with increasing specimen sizes are isolated and discussed. Inconsistencies associated with strain measurements were also identified. Enchanced X-ray radiography was employed for damage evaluation, following step loading. It was shown that fiber dominated layups were less sensitive to scaling effects compared to the matrix dominated layups.

Kellas, Sotiris↗

NASA NTRS1991

Scale selection and propagation of wave-CISK with conditional heating

Analytic solutions are derived for simple models of equatorial wave-CISK with conditional (positive-only) heating. Conditional heating favors an unstable mode having a single wet region of infinitesimal width. This result helps explain model simulations of tropical superclusters and intraseasonal oscillations. Mechanisms of scale selection and propagation are discussed, and the model is generalized to include evaporation-wind feedback, multiple vertical-mode CISK, and scale-dependent damping. The first two mechanisms cause zonal propagation, without scale selection. Scale-dependent damping breaks the inviscid continuum (wherein modes exist as a continuous function of wet region width) into discrete modes with unique horizontal structure and phase speed. Results are contrasted with the hierarchy of scales in observed intraseasonal oscillations.

Dunkerton, Timothy J.↗